Enhanced device performance and stability of perovskite solar cells with low-temperature ZnO/TiO2 bilayered electron transport layers

The instability of perovskite films is a major issue for perovskite solar cells based on ZnO electron transport layers (ETLs). Here, ZnO nanoparticle (NP)- and ZnO sol–gel layers capped with low-temperature processed TiO₂, namely ZnO/TiO₂ bilayered films, have been successfully employed as ETLs in highly efficient MAPbI₃-based perovskite solar cells. It is demonstrated that these ZnO/TiO₂ bilayered ETLs are not only capable of enhancing photovoltaic performance, but also capable of improving device stability. The best device based on the ZnO/TiO₂ bilayered ETL exhibits an efficiency of ∼15% under standard test conditions and can retain nearly 100% of its initial efficiency after 30 days of atmosphere storage, showing much higher device performance and stability compared to those devices based on ZnO single-layer ETLs. Moreover, it is found that perovskite films and devices prepared on the single ZnO sol–gel ETLs are much superior to those deposited on the single ZnO NP-ETLs in both stability and performance, which can be ascribed to fewer surface hydroxyl groups and much smoother surface morphology of the ZnO sol–gel films. The results pave the way for ZnO to be used as an effective ETL of low-temperature processed, efficient and stable PSCs compatible with flexible substrates.

Low-temperature solution-processed ZnO/TiO₂ bilayered films have been demonstrated to be suitable ETLs for highly efficient and stable perovskite solar cells.     

Potassium iodide reduces the stability of triple-cation perovskite solar cells

The addition of alkali metal halides to hybrid perovskite materials can significantly impact their crystallisation and hence their performance when used in solar cell devices. Previous work on the use of potassium iodide (KI) in active layers to passivate defects in triple-cation mixed-halide perovskites has been shown to enhance their luminescence efficiency and reduce current–voltage hysteresis. However, the operational stability of KI passivated perovskite solar cells under ambient conditions remains largely unexplored. By investigating perovskite solar cell performance with SnO₂ or TiO₂ electron transport layers (ETL), we propose that defect passivation using KI is highly sensitive to the composition of the perovskite–ETL interface. We reconfirm findings from previous reports that KI preferentially interacts with bromide ions in mixed-halide perovskites, and – at concentrations >5 mol% in the precursor solution – modifies the primary absorber composition as well as leading to the phase segregation of an undesirable secondary non-perovskite phase (KBr) at high KI concentration. Importantly, by studying both material and device stability under continuous illumination and bias under ambient/high-humidity conditions, we show that this secondary phase becomes a favourable degradation product, and that devices incorporating KI have reduced stability.

The addition of alkali metal halides to hybrid perovskite materials can significantly impact their crystallisation and hence their performance when used in solar cell devices.     

An exclusive deposition method of silver nanoparticles on TiO2 particles via low-temperature decomposition of silver-alkyldiamine complexes in aqueous media

An exclusive deposition method of Ag nanoparticles (NPs) on TiO₂ particles has been developed. Ag NPs supported on TiO₂ particles, Ag_x/TiO₂, with various Ag weight ratios versus total weights of Ag and TiO₂ between x = 2 and 16 wt% are prepared via low-temperature thermal decomposition of Ag(i)–alkyldiamine complexes generated by a reaction between AgNO₃ and N,N-dimethyl-1,3-propanediamine (dmpda) in an aqueous medium suspending TiO₂ particles. The thermal decomposition of the Ag(i)–alkyldiamine complexes is accelerated by TiO₂ particles in the dark, indicating that the reaction catalytically occurs on the TiO₂ surfaces. Under optimised reaction conditions, the thermal decomposition of the complex precursors is completed within 3 hours at 70 °C, and Ag NPs are almost exclusively deposited on TiO₂ particles with high conversion efficiencies (≥95%) of the precursor complexes. The thermal decomposition rates of the precursor complexes are strongly influenced by the chemical structure of a family of water-soluble dmpda analogues, and dmpda with both primary and tertiary amino groups is adopted as a suitable candidate for the exclusive deposition method. The number-averaged particle sizes of the Ag NPs are 6.4, 8.4, 11.8 and 15.2 nm in the cases of Ag_x/TiO₂, x = 2, 4, 8 and 16, respectively. To the best of our knowledge, the as-prepared Ag_x/TiO₂ samples show one of the highest catalytic abilities for the hydrogenation reduction of 4-nitrophenol into 4-aminophenol as a model reaction catalysed by Ag NPs.

The low-temperature decomposition of Ag(i)–dmpda complexes catalytically occurs on TiO₂ surfaces in water.     

UV degradation of the interface between perovskites and the electron transport layer

The stability of the perovskite/electron transport layer (ETL) interface is critical for perovskite solar cells due to the presence of ultraviolet (UV) light in the solar spectrum. Herein, we have studied the decomposition process and performance evolution of the perovskite layer in contact with different ETLs under strong ultraviolet irradiation. The normally used SnO₂ layer has lower photocatalytic activity in comparison with the TiO₂ layer, but the perovskite/SnO₂ interface is still severely decomposed along with the formation of hole structures. Such UV light-induced decomposition, on the one hand, leads to the decomposition of the perovskite phase into PbI₂ and more seriously, the formed hole structure significantly limits the carrier injection at the interface owing to the separation of the perovskite active layer from ETLs. Under the same conditions, the perovskite/PCBM interface is very stable and maintains a highly efficient carrier injection. There is no significant efficiency degradation of the encapsulated PCBM-based devices measured outdoors for about three months.

Using SnO₂ as the ETL in perovskite solar cells can degrade the interface and cause device performance degradation under UV light.     

Efficient photocatalysis with graphene oxide/Ag/Ag2S–TiO2 nanocomposites under visible light irradiation

Lack of visible light response and low quantum yield hinder the practical application of TiO₂ as a high-performance photocatalyst. Herein, we present a rational design of TiO₂ nanorod arrays (NRAs) decorated with Ag/Ag₂S nanoparticles (NPs) synthesized through successive ion layer adsorption and reaction (SILAR) and covered by graphene oxide (GO) at room temperature. Ag/Ag₂S NPs with uniform sizes are well-dispersed on the TiO₂ nanorods (NRs) as evidenced by electron microscopic analyses. The photocatalyst GO/Ag/Ag₂S decorated TiO₂ NRAs shows much higher visible light absorption response, which leads to remarkably enhanced photocatalytic activities on both dye degradation and photoelectrochemical (PEC) performance. Its photocatalytic reaction efficiency is 600% higher than that of pure TiO₂ sample under visible light. This remarkable enhancement can be attributed to a synergy of electron-sink function and surface plasmon resonance (SPR) of Ag NPs, band matching of Ag₂S NPs, and rapid charge carrier transport by GO, which significantly improves charge separation of the photoexcited TiO₂. The photocurrent density of GO/Ag/Ag₂S–TiO₂ NRAs reached to maximum (i.e. 6.77 mA cm⁻²vs. 0 V). Our study proves that the rational design of composite nanostructures enhances the photocatalytic activity under visible light, and efficiently utilizes the complete solar spectrum for pollutant degradation.

The photocatalytic reaction efficiency of GO/Ag/Ag₂S–TiO₂ nanorod arrays is 600% higher than that of a pure TiO₂ sample under visible light.     

Enhanced visible-light photodegradation of fluoroquinolone-based antibiotics and E. coli growth inhibition using Ag–TiO2 nanoparticles

Antibiotics in wastewater represent a growing and worrying menace for environmental and human health fostering the spread of antimicrobial resistance. Titanium dioxide (TiO₂) is a well-studied and well-performing photocatalyst for wastewater treatment. However, it presents drawbacks linked with the high energy needed for its activation and the fast electron–hole pair recombination. In this work, TiO₂ nanoparticles were decorated with Ag nanoparticles by a facile photochemical reduction method to obtain an increased photocatalytic response under visible light. Although similar materials have been reported, we advanced this field by performing a study of the photocatalytic mechanism for Ag–TiO₂ nanoparticles (Ag–TiO₂ NPs) under visible light taking in consideration also the rutile phase of the TiO₂ nanoparticles. Moreover, we examined the Ag–TiO₂ NPs photocatalytic performance against two antibiotics from the same family. The obtained Ag–TiO₂ NPs were fully characterised. The results showed that Ag NPs (average size: 23.9 ± 18.3 nm) were homogeneously dispersed on the TiO₂ surface and the photo-response of the Ag–TiO₂ NPs was greatly enhanced in the visible light region when compared to TiO₂ P25. Hence, the obtained Ag–TiO₂ NPs showed excellent photocatalytic degradation efficiency towards the two fluoroquinolone-based antibiotics ciprofloxacin (92%) and norfloxacin (94%) after 240 min of visible light irradiation, demonstrating a possible application of these particles in wastewater treatment. In addition, it was also proved that, after five Ag–TiO₂ NPs re-utilisations in consecutive ciprofloxacin photodegradation reactions, only a photocatalytic efficiency drop of 8% was observed. Scavengers experiments demonstrated that the photocatalytic mechanism of ciprofloxacin degradation in the presence of Ag–TiO₂ NPs is mainly driven by holes and ˙OH radicals, and that the rutile phase in the system plays a crucial role. Finally, Ag–TiO₂ NPs showed also antibacterial activity towards Escherichia coli (E. coli) opening the avenue for a possible use of this material in hospital wastewater treatment.

Ag nanoparticles decorated-TiO₂ P25 are a viable alternative for the degradation, through a rutile-mediated mechanism, of fluoroquinolone-based antibiotics under visible light irradiation and, at the same time, for bacteria inactivation in water.     

Surface plasmon-driven photoelectrochemical water splitting of a Ag/TiO2 nanoplate photoanode

A silver/titanium dioxide nanoplate (Ag/TiO₂ NP) photoelectrode was designed and fabricated from vertically aligned TiO₂ nanoplates (NP) decorated with silver nanoparticles (NPs) through a simple hydrothermal synthesis and electrodeposition route. The electrodeposition times of Ag NPs on the TiO₂ NP were crucial for surface plasmon-driven photoelectrochemical (PEC) water splitting performance. The Ag/TiO₂ NP at the optimal deposition time of 5 min with a Ag element content of 0.53 wt% demonstrated a remarkably high photocurrent density of 0.35 mA cm⁻² at 1.23 V vs. RHE under AM 1.5G illumination, which was 5 fold higher than that of the pristine TiO₂ NP. It was clear that the enhanced light absorption properties and PEC performance for Ag/TiO₂ NP could be effectively adjusted by simply controlling the loading amounts of metallic Ag NPs (average size of 10–30 nm) at different electrodeposition times. The superior PEC performance of the Ag/TiO₂ NP photoanode was attributed to the synergistic effects of the plasmonic Ag NPs and the TiO₂ nanoplate. Interestingly, the plasmonic effect of Ag NPs not only increased the visible-light response (λ_max = 570 nm) of TiO₂ but also provided hot electrons to promote photocurrent generation and suppress charge recombination. Importantly, this study offers a potentially efficient strategy for the design and fabrication of a new type of TiO₂ hybrid nanostructure with a plasmonic enhancement for PEC water splitting.

A hybrid nanostructure Ag/TiO₂ photoelectrode for PEC water splitting with a remarkable high photocurrent density, 0.35 mA cm⁻² (5 fold higher than that of the pristine TiO₂ photoeletrode) was fabricated by a facile one-pot hydrothermal and electrodeposition method.     

Graphene assisted crystallization and charge extraction for efficient and stable perovskite solar cells free of a hole-transport layer

In recent times, perovskite solar cells (PSCs) have been of wide interest in solar energy research, which has ushered in a new era for photovoltaic power sources through the incredible enhancement in their power conversion efficiency (PCE). However, several serious challenges still face their high efficiency: upscaling and commercialization of the fabricated devices, including long-term stability as well as the humid environment conditions of the functional cells. To overcome these obstacles, stable graphene (G) materials with tunable electronic features have been used to assist the crystallization as well as the charge extraction inside the device configuration. Nonetheless, the hole transport layer (HTL)-free PSCs based on graphene materials exhibit unpredictable results, including a high efficiency and long-term stability even in the conditions of an ambient air atmosphere. Herein, we combine graphene materials into a mesoporous TiO₂ electron transfer layer (ETL) to improve the coverage and crystallinity of the perovskite material and minimize charge recombination to augment both the stability and efficiency of the fabricated mixed cation PSCs in ambient air, even in the absence of a HTL. Our results demonstrate that an optimized PSC in the presence of different percentages of graphene materials displays a PCE of up to 17% in the case of a G:TiO₂ ETL doped with 1.5% graphene. With this coverage and crystallinity amendment approach, we show hysteresis-free and stable PSCs, with less decomposition after ∼3000 h of storage under a moist ambient atmosphere. This work focuses on the originalities of the materials, expenses, and the assembling of stable and effective perovskite solar cells.

In recent times, perovskite solar cells (PSCs) have been of wide interest in solar energy research, which has ushered in a new era for photovoltaic power sources through the incredible enhancement in their power conversion efficiency (PCE).     

The roles of fused-ring organic semiconductor treatment on SnO2 in enhancing perovskite solar cell performance

It took only 11 years for the power conversion efficiency (PCE) of perovskite solar cells (PSCs) to increase from 3.8% to 25.2%. It is worth noting that, as a new thin-film solar cell technique, defect passivation at the interface is crucial for the PSCs. Decorating and passivating the interface between the perovskite and electron transport layer (ETL) is an effective way to suppress the recombination of carriers at the interface and improve the PCE of the device. In this work, several acceptor–donor–acceptor (A–D–A) type fused-ring organic semiconductors (FROS) with indacenodithiophene (IDT) or indacenodithienothiophene (IDDT) as the bridging donor moiety and 1,3-diethyl-2-thiobarbituric or 1,1-dicyromethylene-3-indanone as the strong electron-withdrawing units, were deposited on the SnO₂ ETL to prepare efficient planar junction PSCs. The PCEs of the PSCs increased from 18.63% for the control device to 19.37%, 19.75%, and 19.32% after modification at the interface by three FROSs. Furthermore, impedance spectroscopy, steady-state and time-resolved photoluminescence spectra elucidated that the interface decorated by FROSs enhance not only the extraction of electrons but also the charge transportation at the interface between the perovskite and ETL. These results can provide significant insights in improving the perovskite/ETL interface and the photovoltaic performance of PSCs.

A series of n-type FROSs called IDT-T, IDT-I, and IDDT-T were used to passivate the interface between the perovskite layer and SnO₂ layer in PSCs, leading to reduced interfacial loss in hopes of enhancing the performance of PSCs.     

Electron transport layer assisted by nickel chloride hexahydrate for open-circuit voltage improvement in MAPbI3 perovskite solar cells

SnO₂ is a promising electron transport layer (ETL) material with important applications in planar perovskite solar cells (PSCs). However, electron–hole recombination and charge extraction between SnO₂ and the perovskite layer necessitates further exploration. Nickel chloride hexahydrate (NiCl₂·6H₂O) was introduced into the SnO₂ ETL, which significantly increased the power conversion efficiency (PCE) from 15.49 to 17.36% and the open-circuit voltage (V_OC) from 1.078 to 1.104 V. The improved PCE and V_OC were attributed to the reduced defect states and increased energy level of the conduction band minimum. This work provides new insights into optimizing the V_OC and PCE of PSCs.

Nickel chloride hexahydrate (NiCl₂·6H₂O) was introduced into the SnO₂ ETL, which significantly increased open-circuit voltage (V_OC) and power conversion efficiency (PCE)     

Low-temperature solution-processed SnO2 electron transport layer modified by oxygen plasma for planar perovskite solar cells

SnO₂ has attracted significant attention as an electron transport layer (ETL) because of its wide optical bandgap, electron mobility, and transparency. However, the annealing temperature of 180 °C–200 °C, as reported by several studies, for the fabrication of SnO₂ ETL limits its application for flexible devices. Herein, we demonstrated that the low-temperature deposition of SnO₂ ETL and further surface modification with oxygen plasma enhances its efficiency from 2.3% to 15.30%. Oxygen plasma treatment improves the wettability of the low-temperature processed SnO₂ ETL that results in a larger perovskite grain size. Hence, oxygen plasma treatment effectively improves the efficiency of perovskite solar cells at a low temperature and is compatible with flexible applications.

A simple and effective oxygen plasma treatment on low-temperature deposited SnO₂ electron transport layer was demonstrated.     

High-detectivity perovskite-based photodetector using a Zr-doped TiOx cathode interlayer

We investigated the incorporation of Zr into TiO_x cathode interlayers used as hole-blocking layers in an organometallic halide perovskite-based photodetector. The device configuration is ITO/PEDOT:PSS/CH₃NH₃PbI_xCl_3−x/PC₆₀BM/Zr–TiO_x/Al. The use of Zr–TiO_x in the perovskite photodetector reduces the leakage current and improves carrier extraction. The performance of the perovskite photodetector was confirmed by analyzing the current–voltage characteristics, impedance behaviors, and dynamic characteristics. The device with a Zr–TiO_x layer has a high specific detectivity of 1.37 × 10¹³ Jones and a bandwidth of 2.1 MHz at a relatively low reverse bias and light intensity. Therefore, it can be effectively applied to devices such as image and optical sensors.

The use of Zr–TiO_x in the perovskite photodetector reduces the leakage current and improves carrier extraction.     

A straightforward chemical approach for excellent In2S3 electron transport layer for high-efficiency perovskite solar cells

Perovskite solar cells (PSCs) have attracted significant attention in recent years owing to some of their advantages: high-efficiency, low cost and ease of fabrication. In perovskite photovoltaic devices, charge transport layers play a vital role for selectively extracting and transporting photo-generated electrons and holes to opposite electrodes. Therefore, it is very important to prepare high-quality charge transport layers using simple processes at low cost. As reported, In₂S-based electron selective layers display excellent performance including high solar-cell efficiency and negligible hysteresis. In this study, a simple chemical method was developed to prepare In₂S₃ thin films as the electron selective layers in organic–inorganic hybrid perovskite photovoltaic devices to shorten the fabrication time and simplify the technology, which can provide a new avenue for a low-cost and solution-processed method. By optimizing the preparation conditions, it was demonstrated that In₂S₃ thin film prepared using our straightforward chemical approach have higher electron extraction efficiency and comparable efficiency compared with archetypical TiO₂ as the electron transport layer (ETL) in perovskite photovoltaic device.

A simple, time-saving solution-processed In₂S₃ thin film was applied in perovskite solar cells as the electron selective layer.     

Optimization of the electron transport in quantum dot light-emitting diodes by codoping ZnO with gallium (Ga) and magnesium (Mg)

In our study, to optimize the electron–hole balance through controlling the electron transport layer (ETL) in the QD-LEDs, four materials (ZnO, ZnGaO, ZnMgO, and ZnGaMgO NPs) were synthesized and applied to the QD-LEDs as ETLs. By doping ZnO NPs with Ga, the electrons easily inject due to the increased Fermi level of ZnO NPs, and as Mg is further doped, the valence band maximum (VBM) of ZnO NPs deepens and blocks the holes more efficiently. Also, at the interface of QD/ETLs, Mg reduces non-radiative recombination by reducing oxygen vacancy defects on the surface of ZnO NPs. As a result, the maximum luminance (L_max) and maximum luminance efficiency (LE_max) of QD-LEDs based on ZnGaMgO NPs reached 43 440 cd m⁻² and 15.4 cd A⁻¹. These results increased by 34%, 10% and 27% for the L_max and 450%, 88%, and 208% for the LE_max when compared with ZnO, ZnGaO, and ZnMgO NPs as ETLs.

Optimized QD-LEDs are fabricated using Ga–Mg-codoped ZnO NPs as ETL, which reached the LE_max and PE_max at 15.4 cd A⁻¹ and 10.3 lm W⁻¹.     

Improved performance and stability of perovskite solar cells with bilayer electron-transporting layers

Zinc oxide nanoparticles (NPs) are very promising in replacing the phenyl-C₆₁-butyric acid methyl ester (PC₆₁BM) as electron-transporting materials due to the high carrier mobilities, superior stability, low cost and solution processability at low temperatures. The perovskite/ZnO NPs heterojunction has also demonstrated much better stability than perovskite/PC₆₁BM, however it shows lower power conversion efficiency (PCE) compared to the state-of-art devices based on perovskite/PCBM heterojunction. Here, we demonstrated that the insufficient charge transfer from methylammonium lead iodide (MAPbI₃) to ZnO NPs and significant interface trap-states lead to the poor performance and severe hysteresis of PSC with MAPbI₃/ZnO NPs heterojunction. When PC₆₁BM/ZnO NPs bilayer electron transporting layers (ETLs) were used with a device structure of ITO/poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine) (PTAA)/MAPbI₃/PC₆₁BM/ZnO NPs/Al, which can combine the advantages of efficient charge transfer from MAPbI₃ to PC₆₁BM and excellent blocking ability of ZnO NPs against oxygen, water and electrodes, highly efficient PSCs with PCE as high as 17.2% can be achieved with decent stability.

Perovskite solar cells with PC₆₁BM/ZnO nanoparticles bilayer electron-transporting layers were achieved with a power conversion efficiency of 17.2% and decent stability.

Organic–inorganic hybrid perovskite solar cells (PSCs) have recently attracted tremendous attention because of their excellent photovoltaic efficiencies.^1–4 Since the initial results published in 2009 with efficiencies about 4% using a typical dye-sensitized solar cell structure with liquid electrolyte,⁵ significant progress has been made in device performance through developing high quality film processing methods,^6–10 tuning the perovskite composition,^11–15 optimizing the device architectures^16,17 and synthesizing new hole/electron transport materials.^18–21 Recently, a certified record power conversion efficiency (PCE) of 22.7% was achieved.²² Despite of the success in obtaining dramatically improved PCE, there are certain concerns about the stability and cost towards commercialization. For the state-of-the-art PSCs, perovskites are susceptible to degradation in moisture and air, thus the charge transport materials should prevent the perovskite from exposure to such environments.^20,23–25 One the other hand, PSCs also suffer from the high cost of widely used organic charge transport materials such as 2,2,7,7-tetrakis(N,N-di-p-methoxyphenylamine)-9,9-spirobifluorene (spiro-OMeTAD), phenyl-C_61/71-butyric acid methyl ester (PC_61/71BM).^3,18,26 As alternatives, inorganic materials such as CuSCN,²⁷ CuI,²⁸ CuGaO₂,²⁰ and NiO_x ^29,30 which can be acted as hole transport materials and ZnO,^31,32 SnO₂ ^12,33,34 and TiO₂ ^10,35 which can be acted as electron transport materials are widely studied. Among them, metal oxide nanoparticles (NPs) are very promising in replacing the organic counterparts due to the high carrier mobilities, superior stability, low cost and solution processability at low temperatures.^16,31,33The perovskite/ZnO NPs heterojunction has been demonstrated much better stability than perovskite/PCBM,²³ however it shows lower PCE compared to the state-of-art devices based on perovskite/PCBM heterojunction.^36–38 Thus in this paper, we systematically studied the charge transfer and recombination at CH₃NH₃PbI₃ (MAPbI₃) and ZnO NPs or PC₆₁BM interfaces and tried to fabricate devices with high PCE and super stability simultaneously. We demonstrated that insufficient charge transfer from MAPbI₃ to ZnO NPs and significant interface trap-states lead to the poor performance and severe hysteresis of PSCs based on MAPbI₃/ZnO NPs heterojunction, while the devices based on MAPbI₃/PC₆₁BM show high PCE and negligible hysteresis due to the efficient charge transfer from MAPbI₃ to PC₆₁BM and less recombination at the interface. On the other hand, the MAPbI₃/ZnO NPs devices show excellent stability in air because of the excellent capping ability of ZnO NPs while the stability of MAPbI₃/PC₆₁BM devices is very poor. Thus, we fabricated the PSCs with bilayer electron-transporting layers (ETLs) with the device structure of ITO/poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine) (PTAA)/MAPbI₃/PC₆₁BM/ZnO NPs/Al, trying to combine the advantages of efficient charge extraction ability of PC₆₁BM and excellent blocking ability of ZnO NPs against oxygen, water and electrode, and finally device with PCE as high as 17.2% was achieved with decent stability.     

Metal oxide nanoparticle-modified ITO electrode for high-performance solution-processed perovskite photodetectors

Low dark current density plays a key role in determining the overall performance of perovskite photodetectors (PPDs). To achieve this goal, a hole transport layer (HTL) on the ITO side and a hole blocking layer (HBL) on the metal electrode side are commonly introduced in PPDs. Unlike traditional approaches, we realized a high-performance solution-processed broadband PPD using metal oxide (MO) nanoparticles (NPs) as the HBL on the ITO electrode and PC₆₁BM as another HBL on the metal electrode side to reduce the device dark current. The PPDs based on TiO₂ and SnO₂ NP-modified layers show similar device performances at −0.5 V: a greater than 10⁵ on/off ratio; over 100 dB linear dynamic range (LDR) under different visible light illumination; around 0.2 A W⁻¹ responsivity (R); greater than 10¹² jones detectivity (D*); and ∼20 μs rise time of the device. The MO NP interfacial layer can significantly suppress charge injection in the dark, while the accumulated photogenerated charges at the interface between the MO layer and the perovskite layer introduce band bending, leading to dramatically increased current under illumination. Therefore, the dark current density of the devices is significantly reduced and the optical gain is drastically enhanced. However, after UV illumination, the dark current of the TiO₂ device dramatically increases while the dark current of the SnO₂ device can stay the same as before since the UV illumination-induced conductivity and barrier height changes in the TiO₂ layer cannot recover after removing the UV irradiation. These results indicate that the TiO₂ NP layer is suitable for making a vis-NIR photodetector, while the SnO₂ NP layer is a good candidate for UV-vis-NIR photodetectors. The facile solution-processed high-performance perovskite photodetector using MO NP-modified ITO is highly compatible with low cost, flexible, and large-area electronics.

PPDs based on TiO₂ and SnO₂ NP layers show similar significantly low dark current density. Due to the UV induced conductivity and barrier height changes in the TiO₂ device after UV illumination the dark current of the device increases, while the SnO₂ device remains the same.     

Rapid green-synthesis of TiO2 nanoparticles for therapeutic applications

Nanoparticles (NPs) with sizes ranging from 2 nm to 1 μm find various applications in the field of theranostics. Moreover, if eco-friendly methods are opted for the synthesis of biocompatible and less toxic NPs, then that''s a huge success. Titanium dioxide nanoparticles (TiO₂ NPs) have been vigorously studied for their use in medical implants, photodynamic therapy, drug delivery, biosensing and as antimicrobial agents. The present study reports the green-synthesis of TiO₂ NPs for the first-time using extracts of black pepper (Piper nigrum), coriander (Coriandrum sativum) and clove (Syzygium aromaticum). All three samples of TiO₂ NPs were synthesized via a modified sol–gel method under similar environmental conditions. Similar treatments were given to the samples. The procedure adopted for the synthesis ensures the use of non-toxic materials, no production of toxic by-products and rapid synthesis of the TiO₂ NPs. The NPs were characterized by X-ray diffraction, high resolution-transmission electron microscopy, energy dispersive spectroscopy, field emission scanning electron microscopy and selected area electron diffraction which confirmed the formation, morphology, crystallinity and size of the TiO₂ NPs. These characterizations displayed the similarity index of all three samples. However, photoluminescence and vibrating sample magnetometer studies highlighted the differences among the three samples. All three samples of NPs obtained had a size range of 5–20 nm. Further, the findings showed that different plant extracts result in TiO₂ NPs with moderately different characteristics. Furthermore, the samples were analysed for their drug-encapsulation efficiency using UV-visible spectrophotometry. Among all three samples, the NPs synthesised using black pepper exhibited the maximum encapsulation efficiency. The study concludes that the plant''s bio-profile is responsible for bringing about changes in the traits of the resulting nanoparticles. Thus, the extracts from different plants have the ability to manipulate the properties of the synthesized NPs. These findings can help to understand the role and importance of the plants in synthesizing NPs for biomedical applications. A further detailed study in this field can help researchers to understand the influence of the plant''s biochemistry in shaping the NPs.

Synthesis of TiO₂ nanoparticles using three different plant extracts results in different properties of the individual samples.     

Using Fomitopsis pinicola for bioinspired synthesis of titanium dioxide and silver nanoparticles,targeting biomedical applications

The current study proposes a bio-directed approach for the formation of titanium oxide and silver nanoparticles (TiO₂ and Ag NPs), using a wild mushroom, Fomitopsis pinicola, identified by 18S ribosomal RNA gene sequencing (gene accession no. {"type":"entrez-nucleotide","attrs":{"text":"MK635350","term_id":"1591624388","term_text":"MK635350"}}MK635350) and phenotypic examination. NP synthesis was confirmed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), diffuse reflectance UV-visible spectroscopy (DR-UV), and scanning and transmission electron microscopy (SEM/TEM). Furthermore, the impact of NPs on Escherichia coli and Staphylococcus aureus and a human colon cancer cell line (HCT) were evaluated by MIC/MBC and MTT assays, respectively, along with structural morphogenesis by different microscopy methods. The results obtained showed that TiO₂ and Ag NPs were found to be significantly active, however, slightly enhanced antibacterial and anticancer action was seen with Ag NPs (10–30 nm). Such NPs can be utilized to control and treat infectious diseases and colon cancer and therefore have potential in a range of biomedical applications.

This study proposes a bio-directed approach for the formation of titanium oxide and silver nanoparticles (TiO₂ and Ag NPs), using a wild mushroom, Fomitopsis pinicola, identified by 18S ribosomal RNA gene sequencing (gene accession no. {"type":"entrez-nucleotide","attrs":{"text":"MK635350","term_id":"1591624388","term_text":"MK635350"}}MK635350) and phenotypic examination.     

Stability of MAPbI3 perovskite grown on planar and mesoporous electron-selective contact by inverse temperature crystallization

Single crystalline perovskite solar cells (PSC) are promising for their inherent stability due to the absence of grain boundaries. While the development of single crystals of perovskite with enhanced optoelectronic properties is known, studies on the growth, device performance and understanding of the intrinsic stability of single crystalline perovskite thin film solar cell devices fabricated on electron selective contacts are scarcely explored. In this work, we examine the impact of mesoporous TiO₂ (m-TiO₂) and planar TiO₂ (p-TiO₂) on the growth of single crystalline-methyl ammonium lead iodide (SC-MAPbI₃) film, PSC device performance and film stability under harsh weather conditions (T ∼ 85 °C and RH ∼ 85%). Self-grown SC-MAPbI₃ films are developed on m-TiO₂ and p-TiO₂ by inverse temperature crystallization under ambient conditions without the need for sophisticated glove-box processing. The best device with m-TiO₂ as an electron transport layer showed a promising power conversion efficiency of 3.2% on an active area of 0.3 cm² in hole transport material free configuration, whereas, only 0.7% was achieved for the films developed on p-TiO₂. Complete conversion of precursor to perovskite phase and better surface coverage of the film leading to enhanced absorption and reduced defects of single crystalline perovskite on m-TiO₂ compared to its p-TiO₂ leads to this large difference in efficiency. Mesoporous device retained more than 70% of its initial performance when stored at 30 °C under dark for more than 5000 h at 50% RH; while the planar device degraded after 1500 h. Thermal and moisture endurance of SC-MAPbI₃ films are investigated by subjecting them to temperatures ranging from 35 °C to 85 °C at a constant relative humidity (RH) of 85%. X-ray diffraction studies show that the SC-MAPbI₃ films are stable even at 85 °C and 85% RH, with only slight detection (30–35%) of PbI₂ at these conditions. This study highlights the superior stability of SC-MAPbI₃ films which paves way for further studies on improving the stability and performance of the ambient processed PSCs.

MAPbI₃ film grown on mesoporous TiO₂ showed better crystallinity, performance and stability compared to its planar counterpart.     

Enhancing the thermal stability of the carbon-based perovskite solar cells by using a CsxFA1−xPbBrxI3−x light absorber

Despite the impressive photovoltaic performance with a power conversion efficiency beyond 23%, perovskite solar cells (PSCs) suffer from poor long-term stability, failing by far the market requirements. Although many efforts have been made towards improving the stability of PSCs, the thermal stability of PSCs with CH₃NH₃PbI₃ as a perovskite and organic hole-transport material (HTM) remains a challenge. In this study, we employed the thermally stable (NH₂)₂CHPbI₃ (FAPbI₃) as the light absorber for the carbon-based and HTM-free PSCs, which can be fabricated by screen printing. By introducing a certain amount of CsBr (10%) into PbI₂, we obtained a phase-stable Cs_xFA_1−xPbBr_xI_3−x perovskite by a “two-step” method and improved the device power conversion efficiency from 10.81% to 14.14%. Moreover, the as-prepared PSCs with mixed-cation perovskite showed an excellent long-term stability under constant heat (85 °C) and thermal cycling (−30 °C to 85 °C) conditions. These thermally stable and fully-printable PSCs would be of great significance for the development of low-cost photovoltaics.

Mixed-cation Cs_xFA_1–xPbBr_xI_3–x perovskite was used as light absorber for the carbon-based perovskite solar cells, and the as-prepared solar devices showed excellent long-term stability under constant heat (85 °C) and thermal cycling (−30 °C to 85 °C) condition.