Designing dithienonaphthalene based acceptor materials with promising photovoltaic parameters for organic solar cells

Scientists are focusing on non-fullerene based acceptors due to their efficient photovoltaic properties. Here, we have designed four novel dithienonaphthalene based acceptors with better photovoltaic properties through structural modification of a well-known experimentally synthesized reference compound R. The newly designed molecules have a dithienonaphthalene core attached with different acceptors (end-capped). The acceptor moieties are 2-(5,6-difluoro-2-methylene-3-oxo-2,3-dihydroinden-1-ylidene)malononitrile (H1), 2-(5,6-dicyano-2-methylene-3-oxo-2,3-dihydroinden-1-ylidene)-malononitrile (H2), 2-(5-methylene-6-oxo-5,6-dihydrocylopenta[c]thiophe-4-ylidene)-malononitrile (H3) and 2-(3-(dicyanomethylene)-2,3-dihydroinden-1-yliden)malononitrile (H4). The photovoltaic parameters of the designed molecules are discussed in comparison with those of the reference R. All newly designed molecules show a reduced HOMO–LUMO energy gap (2.17 eV to 2.28 eV), compared to the reference R (2.31 eV). Charger transfer from donor to acceptor is confirmed by a frontier molecular orbital (FMO) diagram. All studied molecules show extensive absorption in the visible region and absorption maxima are red-shifted compared to R. All investigated molecules have lower excitation energies which reveal high charge transfer rates, as compared to R. To evaluate the open circuit voltage, the designed acceptor molecules are blended with a well-known donor PBDB-T. The molecule H3 has the highest V_oc value (1.88 V). TDM has been performed to show the behaviour of electronic excitation processes and electron hole location between the donor and acceptor unit. The binding energies of all molecules are lower than that of R. The lowest is calculated for H3 (0.24 eV) which reflects the highest charge transfer. The reorganization energy value for both the electrons and holes of H2 is lower than R which is indicative of the highest charge transfer rate.

We have designed dithienonaphthalene based A–D–A materials for higher PCE. Our designed molecules have same donor unit with different end-capped acceptor units. All designed molecules are investigated with DFT and TD-DFT approaches.     

Designing indacenodithiophene based non-fullerene acceptors with a donor–acceptor combined bridge for organic solar cells

Non-fullerene small acceptor molecules have gained significant attention for application in organic solar cells owing to their advantages over fullerene based acceptors. Efforts are continuously being made to design novel acceptors with greater efficiencies. Here, optoelectronic properties of four novel acceptor–donor–acceptor (A–D–A) type small molecules (A1, A2, A3 and A4) were studied for their applications in organic solar cells. These molecules contain an indacenodithiophene central core unit joined to different end capped acceptors through a monofluoro substituted benzothiadiazole (FBT) donor acceptor (DA) bridge. The different end capped acceptor groups are; 2-2(2-ethylidene-5,6-difluoro-3-oxo-2,3-dihydroinden-1-ylidene)malononitrile (A1), 2-2(2-ethylidene-3-oxo-2,3-dihydroinden-1-ylidene)malononitrile (A2), 2-(5-ethylidene-6-oxo-5,6-dihydrocyclopenta-b-thiophene-4-ylidene)malononitrile (A3), and 2-2(2-ethylidene-5,6-dicyano-3-oxo-2,3-dihydroinden-1-ylidene)malononitrile (A4). The calculated optoelectronic properties of the designed molecules were compared with a well-known reference compound R, which was recently synthesized and reported as being an excellent A–D–A type acceptor molecule. All designed molecules showed the appropriate frontier molecular orbital diagram for a charge transfer. A4 shows the highest absorption maximum (λ_max) of 858.6 nm (in chloroform solvent), which was attributed to the strong electron withdrawing end-capped acceptor group. Among all of the designed molecules, A3 exhibits the highest open circuit voltages (V_oc) which was (1.84 V) with PTB7-Th and (1.76 V) with the P3HT donor polymer. Owing to a lower value of λ_e with respect to λ_h, the designed molecules demonstrated superior electron mobilities when compared with reference R. Among all of the molecules, A4 shows the highest electron mobility owing to the lower value of λ_e compared to R.

Non-fullerene small acceptor molecules have gained significant attention for application in organic solar cells owing to their advantages over fullerene based acceptors.     

Diketopyrrolopyrrole-based acceptors with multi-arms for organic solar cells

Three small molecules SBF-1DPPDCV, SBF-2DPPDCV and SBF-4DPPDCV consisting of a spirobifluorene (SBF) unit as the core and one, two, and four diketopyrrolopyrrole dicyanovinyl (DPPDCV) units as the arms have been designed and synthesized for solution-processed bulk-heterojunction (BHJ) solar cells. The UV-Vis absorption and cyclic voltammetry measurement of these compounds showed that all these compounds have an intense absorption band over 300–750 nm with a LUMO energy level at around −3.87 eV. When pairing with PTB7-Th as the donor, devices fabricated based on PTB7-Th : SBF-4DPPDCV blends showed a decent PCE of 3.85%, which is the highest power conversion efficiency (PCE) amongst the three DPP acceptor fabricated devices without extra treatment. Devices with SBF-1DPPDCV and SBF-2DPPDCV acceptors showed lower PCEs of 0.26% for SBF-1DPPDCV and 0.98% for SBF-2DPPDCV respectively. The three dimensional (3D) structure of SBF-4DPPDCV facilitates the formation of a 3D charge-transport network and thus enables a rational electron-transport ability (1.04 × 10⁻⁴ cm² V⁻¹ s⁻¹), which further leads to a higher J_sc (10.71 mA cm⁻²). These findings suggest that multi-arm acceptors present better performance than one-arm or two-arm molecules for organic solar cells.

Three diketopyrrolopyrrole-based small molecule acceptors consisting of a spirobifluorene (SBF) core unit and diketopyrrolopyrrole dicyanovinyl (DPPDCV) units as the arms have been synthesized for organic solar cells.     

Quantum chemical modification of indaceno dithiophene-based small acceptor molecules with enhanced photovoltaic aspects for highly efficient organic solar cells

In this computational work, with the aim of boosting the ultimate efficiency of organic photovoltaic cells, seven small acceptors (IDST1–IDST7) were proposed by altering the terminal-acceptors of reference molecule IDSTR. The optoelectronic characteristics of the IDSTR and IDST1–IDST7 molecules were investigated using the MPW1PW91/6-31G(d,p) level of theory, and solvent-state computations were examined using time-dependent density functional theory (TD-DFT) simulation. Nearly all the investigated photovoltaic aspects of the newly proposed molecules were found to be better than those of the IDSTR molecule e.g. in comparison to IDSTR, IDST1–IDST7 exhibit a narrower bandgap (E_gap), lower first excitation energy (E_x), and a significant red-shift in the absorbance maxima (λ_max). According to the findings, IDST3 has the lowest E_x (1.61 eV), the greatest λ_max (770 nm), and the shortest E_gap (2.09 eV). IDST1–IDST7 molecules have higher electron mobility because their RE of electrons is less than that of IDSTR. Hole mobility of IDST2–IDST7 is higher than that of the reference owing to their lower RE for hole mobility than IDSTR. By coupling with the PTB7-Th donor, the open circuit voltage (V_OC) of the investigated acceptor molecules (IDSTR and IDST1–IDST7) was calculated and investigation revealed that IDST4–IDST6 molecules showed higher V_OC and fill factor (FF) values than IDSTR molecules. Accordingly, the modified molecules can be seriously evaluated for actual use in the fabrication of OSCs with enhanced photovoltaic and optoelectronic characteristics in light of the findings of this study.

In this work, with the aim of boosting the ultimate efficiency of organic solar cells, seven small acceptor molecules (IDST1–IDST7) were proposed by altering the terminal-acceptor of reference molecule IDSTR.     

Synergistic end-capped engineering on non-fused thiophene ring-based acceptors to enhance the photovoltaic properties of organic solar cells

In this study, a series of non-fused thiophene ring-based small molecular acceptors (4T1–4T7) of A-D-A type are developed by the replacement of the end-groups of the 4TR molecule. The optoelectronic characteristics of the 4TR and 4T1–4T7 molecules are investigated employing the MPW1PW91 functional with the 6-31G (d,p) basis set, and solvent-state computations are studied using the TD-SCF. All the parameters estimated in this research are improved to a substantial level for the developed molecules as compared to the 4TR molecule, e.g. all the newly developed molecules have shown a red shift in their maximum absorption (λ_max) and a reduced bandgap compared to the 4TR molecule, with ranges of 646 nm to 692 nm (in chlorobenzene solvent) and 2.34 eV to 2.47 eV, respectively. The reorganization energies of electron and hole mobility for almost all developed molecules are smaller than those for the 4TR molecule, with ranges of 0.00766–0.01034 eV and 0.01324–0.01447 eV, respectively. Hence, all the modified chromophores exhibit better charge capabilities than the 4TR molecule. The charge mobility of almost all the developed molecules is improved because of their reduced reorganization energies. The 4T2 molecule has minimum RE values for both electrons (0.00766) and holes (0.01324). The V_OC values of all acceptor molecules are calculated with respect to the PTB7-Th donor. An elevation in V_OC and FF values is exhibited by the 4T5 and 4T7 molecules. As a result, these end-capped engineered molecules should be proposed for the future manufacturing of highly efficient organic solar cells.

The computational analysis revealed the bathochromic shift of the UV-visible absorption, reduced band gap have and increased LHE of all developed molecules as compared to the reference molecule. V_OC was calculated by making their complex of molecules with PTB7-Th donor.     

High voltage vacuum-processed perovskite solar cells with organic semiconducting interlayers

In perovskite solar cells, the choice of appropriate transport layers and electrodes is of great importance to guarantee efficient charge transport and collection, minimizing recombination losses. The possibility to sequentially process multiple layers by vacuum methods offers a tool to explore the effects of different materials and their combinations on the performance of optoelectronic devices. In this work, the effect of introducing interlayers and altering the electrode work function has been evaluated in fully vacuum-deposited perovskite solar cells. We compared the performance of solar cells employing common electron buffer layers such as bathocuproine (BCP), with other injection materials used in organic light-emitting diodes, such as lithium quinolate (Liq), as well as their combination. Additionally, high voltage solar cells were obtained using low work function metal electrodes, although with compromised stability. Solar cells with enhanced photovoltage and stability under continuous operation were obtained using BCP and BCP/Liq interlayers, resulting in an efficiency of approximately 19%, which is remarkable for simple methylammonium lead iodide absorbers.

The effect of n-type interlayers and electrodes on the voltage and stability of fully vacuum-deposited perovskite solar cells is evaluated.     

Hierarchical TiO2 microspheres composed with nanoparticle-decorated nanorods for the enhanced photovoltaic performance in dye-sensitized solar cells

Hierarchical TiO₂ microspheres composed of nanoparticle-decorated nanorods (NP-MS) were successfully prepared with a two-step solvothermal method. There were three benefits associated with the use of NP-MS as a photoanode material. The decoration of nanoparticles improved the specific surface area and directly enhanced the dye loading ability. Rutile nanorods serving as electron transport paths resulted in fast electron transport and inhibited the charge recombination process. The three-dimensional hierarchical NP-MS structure supplied a strong light scattering capability and good connectivity. Thus, the hierarchical NP-MS combined the beneficial properties of improved scattering capability, dye loading ability, electron transport and inhibited charge recombination. Attributed to these advantages, a photoelectric conversion efficiency of up to 7.32% was obtained with the NP-MS film-based photoanode, resulting in a 43.5% enhancement compared to the efficiency of the P25 film-based photoanode (5.10%) at a similar thickness. Compared to traditional photoanodes with scattering layers or scattering centers, the fabrication process for single layered photoanodes with enhanced scattering capability was very simple. We believe the strategy would be beneficial for the easy fabrication of efficient dye-sensitized solar cells.

Hierarchical NP-MS combines the beneficial properties of improved scattering capability, dye loading ability, electron transport and inhibited charge recombination. The photoelectric conversion efficiency up to 7.32% has been obtained.     

Photochromic organic solar cells based on diarylethenes

Photovoltaic devices that switch color depending on illumination conditions may find application in future smart window applications. Here a photochromic diarylethene molecule is used as sensitizer in a ternary bulk heterojunction blend, employing poly(4-butylphenyldiphenylamine) (poly-TPD) and [6,6]-phenyl-C₆₁-butyric acid methyl ester (PC₆₁BM) for the transport of holes and electrons, respectively. Sandwiched between two electrodes, the blend creates a photochromic photovoltaic device that changes color, light absorption, and photon-to-electron conversion efficiency in the visible spectral range after having been illuminated with UV light.

A diarylethene dye that reversibly changes color upon illumination is used in a switchable photochromic organic solar cell.     

Efficient carbazole-based small-molecule organic solar cells with an improved fill factor

In this study, a new acceptor–donor–acceptor (A–D–A) small molecule, DI3TCz, with carbazole as the central unit and 1,3-indanedione as the end group, was designed and synthesized for application in organic solar cells. In contrast to the molecule DR3TCz with rhodanine as end groups, DI3TCz exhibited deep a LUMO energy level and a nearly unchanged HOMO energy level with a narrow optical band gap of 1.75 eV and red shifted absorption. Compared with DR3TCz, the DI3TCz device showed a PCE of 6.46% with a remaining high V_oc value of 0.97 V, improved J_sc of 10.40 mA cm⁻¹ and a notable FF of 0.65, which is the highest PCE value reported to data for carbazole-based small molecules OPVs.

In this study, a new acceptor–donor–acceptor (A–D–A) small molecule, DI3TCz, with carbazole as the central unit and 1,3-indanedione as the end group, was designed and synthesized for application in organic solar cells.     

New ferrocenyl-containing organic hole-transporting materials for perovskite solar cells in regular (n-i-p) and inverted (p-i-n) architectures

Three triphenylamine derivatives containing ferrocenyl groups (JW6, JW7 and JW8) were synthesized by facile syntheses. Their HOMO levels match the valence band energy of CH₃NH₃PbI₃. The introduction of ferrocenyl was aimed to obtain hole transporting materials with high mobility for perovskite solar cells. JW7 shows higher hole mobility (4.2 × 10⁻⁴ cm² V⁻¹ s⁻¹) than JW6 (1.3 × 10⁻⁴ cm² V⁻¹ s⁻¹) and JW8 (1.5 × 10⁻⁴ cm² V⁻¹ s⁻¹). Their film-forming properties are affected by their molecule structures. The methoxyl and N,N-dimethyl terminal substituents of JW7 and JW8 are beneficial for having better solubility than JW6. The regular mesoporous TiO₂-based perovskite solar cells (n-i-p) and the inverted planar heterojunction perovskite solar cells (p-i-n) fabricated using JW7 show the highest power conversion efficiency of 9.36% and 11.43% under 100 mW cm⁻² AM1.5G solar illumination. For p-i-n cells, the standard HTM PEDOT-based cell reaches an efficiency of 12.86% under the same conditions.

New ferrocene-containing organic HTMs for fabricating perovskite solar cells.     

Alteration of the central core of a DF-PCIC chromophore to boost the photovoltaic applications of non-fullerene acceptor based organic solar cells

Modifying the central core is a very efficient strategy to boost the performance of non-fullerene acceptors. Herein five non-fullerene acceptors (M1–M5) of A–D–D′–D–A type were designed by substituting the central acceptor core of the reference (A–D–A′–D–A type) with different strongly conjugated and electron donating cores (D'') to enhance the photovoltaic attributes of OSCs. All the newly designed molecules were analyzed through quantum mechanical simulations to compute their optoelectronic, geometrical, and photovoltaic parameters and compare them to the reference. Theoretical simulations of all the structures were carried out through different functionals with a carefully selected 6-31G(d,p) basis set. Absorption spectra, charge mobility, dynamics of excitons, distribution pattern of electron density, reorganization energies, transition density matrices, natural transition orbitals and frontier molecular orbitals, respectively of the studied molecules were evaluated at this functional. Among the designed structures in various functionals, M5 showed the most improved optoelectronic properties, such as the lowest band gap (2.18 e V), highest maximum absorption (720 nm), and lowest binding energy (0.46 eV) in chloroform solvent. Although the highest photovoltaic aptitude as acceptors at the interface was perceived to be of M1, its highest band gap and lowest absorption maxima lowered its candidature as the best molecule. Thus, M5 with its lowest electron reorganization energy, highest light harvesting efficiency, and promising open-circuit voltage (better than the reference), amongst other favorable features, outperformed the others. Conclusively, each evaluated property commends the aptness of designed structures to augment the power conversion efficiency (PCE) in the field of optoelectronics in one way or another, which reveals that a central un-fused core having an electron-donating capability with terminal groups being significantly electron withdrawing, is an effective configuration for the attainment of promising optoelectronic parameters, and thus the proposed molecules could be utilized in future NFAs.

Modifying the central core is a very efficient strategy to boost the performance of non-fullerene acceptors.     

Wide-bandgap donor polymers based on a dicyanodivinyl indacenodithiophene unit for non-fullerene polymer solar cells

A wide-bandgap polymer donor with improved efficiency plays an important role in improving the photovoltaic performance of polymer solar cells (PSCs). In this study, two novel wide-bandgap polymer donors, PBDT and PBDT-S, were designed and synthesized based on a dicyanodivinyl indacenodithiophene (IDT-CN) moiety, in which benzo[1,2-b:4,5-b′]dithiophene (BDT) building blocks and IDT-CN are used as electron-sufficient and -deficient units, respectively. In our study, the PBDT and PBDT-S polymer donors exhibited similar frontier-molecular-orbital energy levels and optical properties, and both copolymers showed good miscibility with the widely used narrow-bandgap small molecular acceptor Y6. Non-fullerene polymer solar cells (NF-PSCs) based on PBDT:Y6 exhibited an impressive power conversion efficiency of 10.04% with an open circuit voltage of 0.88 V, a short-circuit current density of 22.16 mA cm⁻² and a fill factor of 51.31%, where the NF-PSCs based on PBDT-S:Y6 exhibited a moderate power conversion efficiency of 6.90%. The enhanced photovoltaic performance, realized by virtue of the improved short-circuit current density, can be attributed to the slightly enhanced electron mobility, higher exciton dissociation rates, more efficient charge collection and better nanoscale phase separation of the PBDT-based device. The results of this work indicate that the IDT-CN unit is a promising building block for constructing donor polymers for high-performance organic photovoltaic cells.

We developed two novel wide-bandgap polymer donors based on an IDT-CN unit with deep HOMO levels for non-fullerene polymer solar cells with 10.04% efficiency.     

Functionalized carboxylate deposition of triphenylamine-based organic dyes for efficient dye-sensitized solar cells

The standard dip-coating dye-loading technique for dye-sensitized solar cells (DSSCs) remains essentially unchanged since modern DSSCs were introduced in 1991. This technique constitutes up to 80% of the DSSC fabrication time. Dip-coating of DSSC dyes not only costs time, but also generates a large amount of dye waste, necessitates use of organic solvents, requires sensitization under dark conditions, and often results in inefficient sensitization. Functionalized Carboxylate Deposition (FCD) was introduced as an alternative dye deposition technique, requiring only 2% of the fabrication time, eliminating the need for solvents, and significantly reducing dye waste. In this study, FCD was used to deposit two relatively large triphenylamine-based organic dyes (L1 and L2). These dyes were sublimated and deposited in <20 minutes via a customized FCD instrument using a vacuum of ∼0.1 mTorr and temperatures ≤280 °C. FCD-based DSSCs showed better efficiency (i.e., 5.03% and 5.46% for L1 and L2 dyes, respectively) compared to dip-coating (i.e., 4.36% and 5.35% for L1 and L2, respectively) in a fraction of the deposition time. With multiple advantages over dip-coating, FCD was shown to be a viable alternative for future ultra-low cost DSSC production.

Functionalized carboxylate deposition involves deposition of molecules from the gas phase and is an alternative dye loading technique to dip-coating. It was used to create a monolayer of large molecular weight dyes on TiO₂, providing multiple advantages to dip-coating.     

Nonfullerene acceptors comprising a naphthalene core for high efficiency organic solar cells

A fused-ring electron acceptor (FREA) NDIC is designed and synthesized. Inspired by IDIC, NDIC was constructed by replacing the benzene with a naphthalene ring in its core unit. IDIC exhibits an optical bandgap of 1.60 eV and a lower lowest unoccupied molecular orbital (LUMO) energy level of −3.92 eV. In comparison, NDIC displays an optical band gap of 1.72 eV and a higher lying LUMO energy level of −3.88 eV. Due to the higher energy level, inverted devices based on NDIC exhibit a higher open circuit voltage (V_oc) of 0.90 V, which is much higher than that of IDIC (0.77 V). After a series of optimizations, a power conversion efficiency (PCE) of 9.43% was obtained with a PBDB-T:NDIC blend active layer, in comparison, a PCE of 9.19% was achieved based on IDIC. Our results demonstrate that a tiny variation in the molecular structure could dramatically affect the optical and electrochemical properties, and thus the photovoltaic performance.

NDIC with a naphthalene ring as the core unit is synthesized and used as an acceptor material to fabricate organic solar cells.     

Interface engineering through electron transport layer modification for high efficiency organic solar cells

In the present study, we have compared the device performance of poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b′]dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thio-phene-)-2-carb-oxylate-2-6-diyl)] (PTB7-Th):phenyl-C71-butyric acid methyl ester (PCBM) organic solar cells (OSCs) in an inverted geometry with ZnO, a bilayer of ZnO and Ba(OH)₂ [ZnO/Ba(OH)₂] and a nanocomposite of ZnO and Ba(OH)₂ [ZnO:Ba(OH)₂] as electron transport layers (ETLs). Our study reveals that the performance of the devices with the ZnO/Ba(OH)₂ and ZnO:Ba(OH)₂ nanocomposite as ETL supersedes that of devices with only ZnO as ETL. The plausible reasons for the improved performance of these devices are identified using morphological studies, contact angle measurements, X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS) and photo-electrochemical impedance spectroscopy (EIS) measurements. It is observed that films of ZnO/Ba(OH)₂ and ZnO:Ba(OH)₂ nanocomposites have a low work function and are slightly more smooth and hydrophobic than ZnO films. This might have suppressed the charge recombination and thereby improved the charge collection as has been confirmed by EIS measurements.

Schematic of PTB7-Th:PCBM OSCs in an inverted geometry with ZnO, ZnO/Ba(OH)₂ and ZnO:Ba(OH)₂ nanocomposites as ETLs.     

Engineering of W-shaped benzodithiophenedione-based small molecular acceptors with improved optoelectronic properties for high efficiency organic solar cells

In the current study, with the objective to improve the overall performance of organic solar cells, seven new W-shaped small molecular acceptors – were developed theoretically by the end-group alteration of the reference (WR) molecule. The MPW1PW91 functional with the basis set 6-31G(d,p) was used to explore the optoelectronic properties of the WR and W1–W7 molecules and the time-dependent self-consistent filed (TD-SCF) simulation was used to investigate the solvent-state calculations. The several explored photovoltaic attributes were the absorption spectra, excitation energies, bandgap between the FMOs, oscillator strength, full width at half maximum, light-harvesting efficiency, transition density matrices, open-circuit voltage, fill factor, density of states, binding energy, interaction coefficient, etc. Overall, the results revealed a bathochromic shift in the absorption maxima (λ_max), a reduced HOMO–LUMO gap (E_gap), and smaller excitation energy (E_x) of the altered molecules as compared to the WR molecule. Some of the optoelectronic aspects of a well-known fused ring based acceptor named Y6 are also compared with the studied W-shaped molecules. Additionally, the W1 molecule presented the smallest E_gap, along with highest λ_max and the lowest E_x, amongst all, in both the evaluated media (gas and solvent). The open circuit voltage (V_OC) of all the considered small molecular acceptors was calculated by pairing them with the PTB7-Th donor. Here, W6 and W7 displayed the best results for the V_OC (1.48 eV and 1.51 eV), normalized V_OC (57.25 and 58.41) and FF (0.9131 and 0.9144). Consequently, in light of the results of this research, the altered molecules could be considered for practical implementation in the manufacturing of OSCs with improved photovoltaic capabilities.

The developed molecules have a reduced band gap and lower excitation energy. Their V_OC was calculated by making complexes of them with the PTB7-Th donor.     

An organic hole-transporting material spiro-OMeTAD doped with a Mn complex for efficient perovskite solar cells with high conversion efficiency

2,{2}′,7,{7}′-Tetrakis(N,N-di-p-methoxyphenylamine)-9,{9}′-spiro-bi-fluorene(spiro-OMeTAD) has often been used as a hole-transporting material (HTM) in mesoscopic perovskite solar cells (PSCs). However, its potential applications are limited due to its poor conductivity of approximately 10⁻⁶ to 10⁻⁵ cm² V s⁻¹ in pristine form, and this influences the stability and intrinsic hole conductivity of the device. In this work, a Mn complex [(Mn(Me-tpen)(ClO₄)₂⁻)]²⁺ is introduced as a p-dopant to improve the properties of spiro-OMeTAD-based PSCs, including the optical, electrical, conductivity, and stability properties. Interestingly, the use of spiro-OMeTAD with an optimum concentration (1.0% w/w) of Mn complex in mesoscopic PSCs achieves a remarkable power conversion efficiency of 17.62% with a high conductivity of 99.05%. Spiro-OMeTAD with Mn complex as a p-dopant under UV-vis spectroscopy shows a different peak at 520 nm, confirming that oxidation occurs upon the addition of the Mn complex. The enhanced efficiency of the PSCs may be attributed to an increase in the optical and electrical properties of the HTM in the spiro-OMeTAD doped Mn complex.

Mesoscopic PSCs utilizing spiro-OMeTAD with different concentrations of a Mn complex were obtained, and the PSC with the optimum Mn-complex concentration (1.0% w/w) achieved a remarkable power conversion efficiency of 17.62%.     

Study on graphene oxide as a hole extraction layer for stable organic solar cells

The development of an efficient and stable hole extraction layer (HEL) is crucial for commercializing organic solar cells (OSCs). Although a few candidates have been widely utilized as HELs for OSCs, the most appropriate material has been lacking. A few articles have recently reported graphene oxide (GO) as a well-working HEL that offers comparable performance to conventional HELs. However, a systematic study providing comprehensive insight into the GO-based OSC behavior is lacking. This article discusses broad topics, including the material properties, device efficiency, shelf lifetime, and impedance properties. We found that GO offers excellent properties, which are identical to those of conventional HELs, while the shelf lifetime shows a significant 6-fold increase. Furthermore, we discuss the significantly reduced space-charge limited region of an aged GO-based OSC compared with a PEDOT:PSS-based device, which is revealed to be a reason for the different shelf lifetime. We believe that the results will accelerate the development of GO as an HEL for OSCs and other optoelectronic devices.

Graphene oxide (GO) offers comparable efficiency in organic solar cells (OSCs) compared to the hole extraction layer (HEL), poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), while the shelf lifetime shows a 6-fold increase.     

Computational study of linear carbon chain based organic dyes for dye sensitized solar cells

Spectroscopic, electronic and electron injection properties of a new class of linear carbon chain (LCC) based organic dyes have been investigated, by means of density functional theory (DFT) and time-dependent density functional theory (TDDFT), for application in dye-sensitized solar cells (DSSCs). The photophysical properties of LCC-based dyes are tuned by changing the length of the linear carbon chain; UV/VIS absorption is red-shifted with increasing LCC length whereas oscillator strength and electron injection properties are reduced. Excellent nonlinear optical properties are predicted in particular for PY-N4 and PY-S4 dyes in the planar conformation. Results indicate that a LCC-bridge produces better results compared to benzene and thiophene bridges. Simulations of I⁻-Dye@(TiO₂)₁₄ and Dye@(TiO₂)₁₄ anatase complexes indicate that designed dyes inject electrons efficiently into the TiO₂ surface and can be regenerated by electron transfer from the electrolyte. Superior properties in terms of efficiency are shown by compounds with a pyrrole ring as the donor group and PY-3N is expected to be a promising candidate for applications, however all the investigated dyes could provide a good performance in solar energy conversion. Our study demonstrates that computational design can provide a significant contribution to experimental work; we expect this study will contribute to future developments to identify new and highly efficient sensitizers.

Photophysical properties of a new family of LCC-based dyes for applications in DSSC are predicted. Superior properties are shown by compounds with pyrrole ring as donor group, PY-3N is expected to be a promising candidate for applications.