Hole-transporting Materials For Perovskite Solar Cells Research Articles

Introducing an Organic Hole Transporting Material as a Bilayer to Improve the Efficiency and Stability of Perovskite Solar Cells

Although perovskite solar cells (PSCs) have achieved high power conversion efficiency (PCE) by utilizing 2,2′,7,7′-tetrakis(N,N′-di-p-methoxyphenylamine)-9,9′-Spirobifluorene (Spiro-OMeTAD) as hole transporting material (HTM), the reproducibility and stability of PSCs are still a pressing concern. Herein, we introduced a solvent processed organic-organic bilayer based on 2-(4-(7-(9,9-dimethylacridin-10(9H)-yl)-9,9-diethyl-9H-fluoren-2-yl)phenyl)-1-phenyl-1H-phenanthro[9,10-d]imidazole (AFpPPI) and Spiro-OMeTAD in layer to layer as HTM in PSCs. The devices configured with AFpPPI/Spiro-OMeTAD bilayer achieved a maximum PCE of 19.9% in mesoporous-TiO2 (mp-TiO2) structure with perovskite absorber of Cs0.05Rb0.05(FAPbI3)0.76 (MAPbBr3)0.14. The properties of the bilayer structure were analyzed with steady-state photoluminescence, ultra-violet photoelectron and impedance spectroscopy. The AFpPPI/Spiro-OMeTAD improved open-circuit voltage (Voc) by lowering the quasi-Fermi energy level for holes and reducing the charge recombination, resulting in high Voc (1.14 V in the champion cell) and high fill factor (FF) that lead to high PCE. The addition of AFpPPI layer improves the quality of Spiro-OMeTAD and provides pinhole-free film. Moreover, the stability is improved in controlled temperature and humid conditions. This work affords a new approach for commercial applications of PSCs with better stability.

Recent progress in inverted perovskite solar cells employing nickel oxide (NiOx) as a hole transport materials

Perovskite solar cells (PSCs) have made phenomenal improvement in the power conversion efficiency from 3.8% in 2009 to 25.2% in 2020. Even though TiO2 continues to be the most used electron transport layer in PSCs, research in the field showed that n- type SnO2 when used on the transparent front electrode with conventional structure (n-i-p) has the highest device efficiency. However, their scope for further commercial application is limited due to the need for high temperature process and the comparatively higher J-V hysteresis in conventional (n-i-p) structure. Therefore, inverted device configuration (p-i-n) using NiOx as a hole transport material (HTM) has drawn considerable interest in the past several years. This is primarily due to their excellent chemical stability, smaller processing temperature for device fabrication, and good transmittance compared to organic HTMs. Deposition of NiOx hole transport material on the FTO/ITO substrate is an efficient way to improve the photo physics of manufacturing devices. It has shown impressive outcomes in inverted PSCs. Recent advances in the preparation of NiOx HTMs are detailed in this article. The impact of NiOx deposition on FTO/ITO substrate by different methods and their effect on electrical and optical properties was carefully studied. We also address the benefits and existing issues of using NiOx HTMs in PSCs and aim to foresee future success by incorporating them in high-efficiency inverted perovskite solar cell architecture.

Improved efficiency and carrier dynamic transportation behavior in perovskite solar cells with CuInS2 quantum dots as hole-transport materials.

Inorganic quantum dot (QD)-based hole-transport materials (HTMs) have proved their potential in perovskite solar cells (PSCs). In this work, CuInS2 quantum dots (CIS QDs) were applied as HTMs for PSCs with the architecture of TiO2/Cs0.17FA0.83Pb(Br0.2I0.8)3/HTM/Au. By optimizing the preparation process, a high-quality perovskite thin film could be obtained. When the speed was 5000 rpm, the speed acceleration was 3000 rpm per s and heat treated at 150 °C, the perovskite film had low surface roughness (15.26 nm) and obvious grain boundary. The photoelectric conversion efficiency (PCE) of PSCs was greatly improved from 2.83% to 12.33% utilizing CIS QDs at an optimal concentration and with surface ligands as HTMs. Surface ligands can control the size and shape of CIS QDs, and thus affect the performance of PSCs. The carrier dynamic transportation behaviour at the CIS/perovskite interface was studied, which showed that CIS QDs as HTMs in PSCs can strongly quench the fluorescence and increase the photobleaching recovery rate. Therefore, CIS QDs are promising inorganic HTMs for the fabrication of PSCs.

Dopant-Free Hole-Transport Materials with Germanium Compounds Bearing Pseudohalide and Chalcogenide Moieties for Perovskite Solar Cells.

Hole-transport materials (HTMs) are key electronic components for the functioning of perovskite solar cells (PSCs) as they extract the photogenerated holes from the perovskite to be transported subsequently to the back electrode while minimizing the loss from electron recombination. Herein, we report the synthesis and characterization of novel germanium-based compounds with [{HC(CMeNAr)2}GeNCS] (2), [{HC(CMeNAr)2}Ge(S)NCS] (3), and [{HC(CMeNAr)2}Ge(Se)NCS] (4) compositions, with Ar = 2,6-iPr2C6H3 and the photovoltaic performance of 3 and 4 that is the same as for HTM in PSC. All compounds displayed excellent thermal properties and an appropriate alignment of energy levels for the perovskite with maximum optical absorption in the near-UV region. As revealed by space-charge limited-current (SCLC) measurements, compounds 3 and 4 have competing hole mobilities of about 1.37 × 10-4 and 4.88 × 10-4 cm2 V-1 s-1, respectively. Upon assessing PSC devices using 3 and 4 with triple-cation perovskite absorber Cs0.05(MA0.17FA0.83)0.95Pb(I0.83Br0.17)3, the power conversion efficiencies (PCEs) were about 13.03 and 9.23%, respectively, both without doping and additives, and were compared with benchmark HTM spiro-OMeTAD (2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene). Quantum chemical calculations with DFT showed that the optoelectronic properties are strongly influenced by the combined contributions of the germanium atom, the pseudohalide moiety (NCS-), and chalcogenides (S2- or Se2-). Fine tuning the electronic properties of germanium is thus a good strategy for the targeted synthesis of potential conducting molecules in PSCs.

N-Substituted Phenothiazines as Environmentally Friendly Hole-Transporting Materials for Low-Cost and Highly Stable Halide Perovskite Solar Cells.

Most of the high-performing halide perovskite solar cells (PSCs) leverage toxic chlorinated solvents (e.g., o-dichlorobenzene or chlorobenzene) for the hole-transporting material (HTM) processing and/or antisolvents in the perovskite film fabrication. To minimize the environmental and health-related hazards, it is highly desirable, yet at the same time demanding, to develop HTMs and perovskite deposition processes relying on nonhalogenated solvents. In this work, we designed two small molecules, AZO-III and AZO-IV, and synthesized them via simple and environmentally friendly Schiff base chemistry, by condensation of electron-donating triarylamine and phenothiazine moieties connected through an azomethine bridge. The molecules are implemented as HTMs in PSCs upon processing in a nonchlorinated (toluene) solvent, rendering their synthesis and film preparation eco-friendly. The enhancement in the power conversion efficiency (PCE) was achieved when switching from AZO-III (9.77%) to AZO-IV (11.62%), in which the thioethyl group is introduced in the 2-position of the phenothiazine ring. Additionally, unencapsulated PSCs based on AZO-III displayed excellent stabilities (75% of the initial PCEs is retained after 6 months of air exposure for AZO-III to be compared with a 48% decrease of the initial PCE for Spiro-OMeTAD-based devices). The outstanding stability and the extremely low production cost (AZO-III = 9.23 $/g and AZO-IV = 9.03 $/g), together with the environmentally friendly synthesis, purification, and processing, make these materials attractive candidates as HTMs for cost-effective, stable, and eco-friendly PSCs.

Air-stable perovskite photovoltaic cells with low temperature deposited NiOx as an efficient hole-transporting material

The electron-beam physical vapor deposition (EBPVD) technique was selected for nickel oxide (NiOx) film deposition at room temperatures. NiOx film (18 nm thick) was deposited as a hole transporting material (HTM) for inverted perovskite solar cells (PSCs) onto a fluorine-doped tin oxide (FTO)-coated glass substrate at a chamber vacuum pressure of 4.6×104 Pa. PSCs were fabricated as a glass/FTO/NiOx(HTM)/CH3NH3PbI3/PC61BM/BCP/Ag structure with as-deposited and annealed (500 °C for 30 min) NiOx films. Under 100 mW cm-2 illumination, as-deposited and annealed NiOx as HTM in PSCs (0.16 cm2) showed a high-power conversion efficiency (PCE) of 13.20% and 13.24%, respectively. The as-deposited and annealed PSCs retained 72.2% and 76.96% of their initial efficiency in ambient conditions, correspondingly. This study highlights the possibility of achieving highly crystalline and finely disseminated NiOx films by EBPVD for fabricating efficient inverted PSCs.

Asymmetric Benzotrithiophene-Based Hole Transporting Materials Provide High-Efficiency Perovskite Solar Cells.

In this study, we synthesized a series of small-molecule benzotrithiophenes (BTTs) and used them as hole transporting materials (HTMs) in perovskite solar cells (PSCs). The asymmetric benzo[2,1-b:-3,4-b':5,6-b″]trithiophene unit was used as the central core to which were appended various donor groups, namely, carbazole (BTT-CB), thieno thiophene (BTT-FT), triphenylamine (BTT-TPA), and bithiophene (BTT-TT). The extended aromatic core in the asymmetric BTT provided full planarity, thereby favoring intermolecular π-stacking and charge transport. The physical, optical, and electrical properties of these small-molecule HTMs are reported herein. BTT-TT displayed good crystallinity and superior hole mobility, when compared with those of the other three HTMs, and formed smooth and uniform surfaces when covering the perovskite active layer. Accordingly, among the devices prepared in this study, a PSC incorporating BTT-TT as the HTM achieved the highest power conversion efficiency (18.58%). Moreover, this BTT-TT-containing device exhibited good stability after storage for more than 700 h. Thus, asymmetric BTTs are promising candidate materials for use as small-molecule HTMs in PSCs.

The use of nickel oxide as a hole transport material in perovskite solar cell configuration: Achieving a high performance and stable device

Solar cells incorporated with organic-inorganic lead or tin halide-based perovskite materials as active light-absorber surfaces are referred to as perovskite solar cells (PSCs). This fast advancing solar technology has recorded an increase in its efficiency from 3.8% in 2009 to above 25% in recent years. The technology creates room for diverse device architectures, which enhances further development of thin-film solar cells and photovoltaics. This article reviews the use of nanocrystalline nickel oxide (NiO) film as a hole transport material in PSCs. The literature on pure nickel oxide and doped nickel oxide films has been discussed. The principle of operation, charge separation of PSCs and the various parameters that affect the efficient hole transport mechanisms, power conversion efficiency, growth mechanism, and stability of PSCs have also been discussed. Possible electron-blocking applications and future perspective of nickel oxide films have also been discussed.

Organic Ionic Plastic Crystals as Hole Transporting Layer for Stable and Efficient Perovskite Solar Cells

AbstractOrganic ionic plastic crystals (OIPCs) are synthesized through a simple metal‐free, cost‐effective approach. The strategized synchronization of electron‐rich phenoxazine with benzimidazolium iodide (OIPC‐I) and bromide (OIPC‐Br) salts lead to enhanced hole mobility and conductivity of OIPCs which is suitable for an efficient alternative to conventional organic hole transporting materials (HTMs) for stable perovskite solar cells (PSCs). The fabricated PSCs with OIPC‐I as hole transporting layer yielded a power conversion efficiency of 15.0% and 18.1% without and with additive (Li salt) respectively, which are comparable with spiro‐OMeTAD based devices prepared under similar conditions. Furthermore, the PSCs with OIPCs show good stability compared to the spiro‐OMeTAD with or without additives. Here, first time benzimidazolium‐based OIPCs have been used as an alternative organic HTM for perovskite solar cells, which opens a window for the design of effective OIPCs for highly efficient PSCs with long‐term stability.

Accurately Stoichiometric Regulating Oxidation States in Hole Transporting Material to Enhance the Hole Mobility of Perovskite Solar Cells

In traditional n‐i‐p‐type perovskite solar cells (PSCs), most hole transporting materials (HTMs) rely on an uncontrolled oxidative process using Li salt and Co (III) complex to achieve sufficient hole mobilities. Herein, a stabilized oxidized phenothiazine‐based HTM (OPTZ) synthesized from its neutral form (NPTZ) through a photoredox reaction is demonstrated. This controllable and stable oxidation state is mainly derived from the planar structure and π conjugation of phenothiazine core in OPTZ. The energy gap between the singly occupied molecular orbital (SOMO) of OPTZ and highest occupied molecular orbital (HOMO) of NPTZ suitably promotes hole hopping in hole transporting layers. Using an optimized ratio of OPTZ as the dopant in NPTZ, the hole transporting mobility is effectively enhanced due to an intra‐ and intermolecular charge transfer process, resulting in an enhancement in the fill factor of the PSCs. Herein, a new strategy to obtain stabilized oxidized HTMs, which deliver significantly enhanced hole mobilities of HTMs in PSCs, is provided.

Dopant-Free Organic Hole-Transporting Material for Efficient and Stable Inverted All-Inorganic and Hybrid Perovskite Solar Cells.

Designing new hole-transporting materials (HTMs) with desired chemical, electrical, and electronic properties is critical to realize efficient and stable inverted perovskite solar cells (PVSCs) with a p-i-n structure. Herein, the synthesis of a novel 3D small molecule named TPE-S and its application as an HTM in PVSCs are shown. The all-inorganic inverted PVSCs made using TPE-S, processed without any dopant or post-treatment, are highly efficient and stable. Compared to control devices based on the commonly used HTM, PEDOT:PSS, devices based on TPE-S exhibit improved optoelectronic properties, more favorable interfacial energetics, and reduced recombination due to an improved trap passivation effect. As a result, the all-inorganic CsPbI2 Br PVSCs based on TPE-S demonstrate a remarkable efficiency of 15.4% along with excellent stability, which is the one of the highest reported values for inverted all-inorganic PVSCs. Meanwhile, the TPE-S layer can also be generally used to improve the performance of organic/inorganic hybrid inverted PVSCs, which show an outstanding power conversation efficiency of 21.0%, approaching the highest reported efficiency for inverted PVSCs. This work highlights the great potential of TPE-S as a simple and general dopant-free HTM for different types of high-performance PVSCs.

Vapor-Phase Formation of a Hole-Transporting Thiophene Polymer Layer for Evaporated Perovskite Solar Cells.

Homogeneous layer formation on textured silicon substrates is essential for the fabrication of highly efficient monolithic perovskite silicon tandem solar cells. From all well-known techniques for the fabrication of perovskite solar cells (PSCs), the evaporation method offers the highest degree of freedom for layer-by-layer deposition independent of the substrate's roughness or texturing. Hole-transporting polymers with high hole mobility and structural stability have been used as effective hole-transporting materials (HTMs) of PSCs. However, the strong intermolecular interactions of the polymers do not allow for a layer formation via the evaporation method, which is a big challenge for the perovskite community. Herein, we first applied a hole-transporting terthiophene polymer (PTTh) as an HTM for evaporated PSCs via an in situ vapor-phase polymerization using iodine (I2) as a sublimable oxidative agent. PTTh showed high hole mobility of 1.2 × 10-3 cm2/(V s) and appropriate energy levels as HTM in PSCs (EHOMO = -5.3 eV and ELUMO = -3.3 eV). The PSCs with the in situ vapor-phase polymerized PTTh hole-transporting layer and a co-evaporated perovskite layer exhibited a photovoltaic conversion efficiency of 5.9%, as a proof of concept, and high cell stability over time. Additionally, the polymer layer could fully cover the pyramidal structure of textured silicon substrates and was identified as an effective hole-transporting material for perovskite silicon tandem solar cells by optical simulation.

Dopant-free hole transport materials processed with green solvent for efficient perovskite solar cells

At present, dopant-free hole transport materials (HTMs) have been largely explored to improve the performance and stability of perovskite solar cells (PSCs), and significant progresses have been made. In current reports, chlorobenzene is the most commonly used solvent to dissolve HTMs in PSCs. Dopant-free HTMs based on green solvent were rarely reported yet. Here in this work we synthesized a new dopant-free HTM F23, which could be processed with the nonhalogenated and environmental-friendly green solvent tetrahydrofuran (THF). Interestingly, F23 film prepared using THF as solvent exhibits uniform and smooth morphology, with excellent hole transport property. In addition, the process requires only a small amount of F23 (3 mg/mL), thus further lowering the costs in device fabrication. As a result, device using dopant-free F23 prepared in THF as HTM exhibited a high power conversion efficiency (PCE) of 17.60%, with enhanced stability.

Hole transport layers based on metal Schiff base complexes in perovskite solar cells

In this report a new series of metal Schiff base complexes (MMePy, M = Pt, Pd and Cu) were synthesized and used as hole transport materials (HTMs) in perovskite solar cells (PSCs), as an attempt to realize the hole extraction and transport ability of these materials in PSCs. The energy levels of the materials can be easily tuned by changing the central metal, leading to a better alignment with the perovskite absorber. The well matching of energy level along with lower surface roughness and higher crystallinity of the thin film give rise to the highest PCE of 8.07 % for the CuMePy-based device among the MMePy-based devices. The result indicates the promising application of this series of metal complexes for the use as HTM in PSCs.

Polymeric, Cost-Effective, Dopant-Free Hole Transport Materials for Efficient and Stable Perovskite Solar Cells.

Perovskite solar cells (PSCs) has skyrocketed in the past decade to an unprecedented level due to their outstanding photoelectric properties and facile processability. However, the utilization of expensive hole transport materials (HTMs) and the inevitable instability instigated by the deliquescent dopants represent major concerns hindering further commercialization. Here, a series of low-cost, conjugated polymers are designed and applied as dopant-free HTMs in PSCs, featuring tuned energy levels, good temperature and humidity resistivity, and excellent photoelectric properties. Further studies highlight the critical and multifaceted roles of the polymers with respect to facilitating charge separation, passivating the surface trap sites of perovskite materials, and guaranteeing long-term stability of the devices. A stabilized power conversion efficiency (PCE) of 20.3% and remarkably enhanced device longevity are achieved using the dopant-free polymer P3 with a low concentration of 5 mg/mL, qualifying the device as one of the best PSC systems constructed on the basis of dopant-free HTMs so far. In addition, the flexible PSCs based on P3 also exhibit a PCE of 16.2%. This work demonstrates a promising route toward commercially viable, stable, and efficient PSCs.

Fluorination of pyrene-based organic semiconductors enhances the performance of light emitting diodes and halide perovskite solar cells

Abstract In this work, a fluorinated pyrene-based organic semiconductor (L-F) has been designed and synthesized starting from a low-cost pyrene core functionalized with triphenilamine substituents at 1,3,6,8 positions (L-H), obtained via Suzuki coupling reactions. Its performance when used as green emitter in organic light emitting diodes (OLEDs) or as dopant-free hole-transporting material (HTM) in halide perovskite solar cells (PSCs) is higher than that of the L-H counterpart, in spite of its lower bulk hole-mobility (7.0 × 10−6 cm2/V) to L-H (1.9 × 10−4 cm2/V). In fact, the OLED devices based on a L-F active layer showed excellent green emission (brightness and current efficiency were 1759.8 cd/m2 and 3.7 cd/A, respectively) at a 4.5 V turn-on voltage. When the molecules were employed as a dopant-free HTM in PSCs, L-F led to a power conversion efficiency (PCE) and open circuit voltage (Voc) of 5.9% and 1.07 V, respectively, thus outperforming those of corresponding devices based on L-H (PCE = 5.0% and Voc = 0.87 V) under similar experimental conditions (AM 1.5G and 100 mW cm2). We attribute the enhancements of L-F-based optoelectronic devices (OLEDs and PSCs) to the observed better quality of the L-F films. The promising performance of L-F indicates that fluorination of small molecules can be an effective strategy to achieve low-cost and high-performing materials for energy harvesting and display-based organic electronic devices.

Promising hole‐transporting materials for perovskite solar cells: Modulation of the electron‐deficient units in triphenylamine derivative‐based molecules

AbstractModulation of the electron‐deficient π‐bridge units in 4‐methoxy‐N‐(4‐methoxyphenyl)‐N‐phenylbenzenamine (MeTPA)‐based hole‐transporting materials (HTMs) is a significant approach to improve hole mobility of HTMs for perovskite solar cells (PSCs). In this study, a class of simple MeTPA‐based HTMs (H1‐H4) with different π‐bridged electron‐deficient units were designed for the purpose of providing a theoretical model to obtain potential MeTPA‐based HTMs. The results indicated that H2 to H4 exhibit better performance, such as larger Stokes shifts, smaller exciton‐binding energy, better stability, good solubility, and higher hole mobility, in comparison with the parental material H1. H2 to H4 materials with high hole mobility (5.45 × 10−4, 2.70 × 10−1, and 3.99 × 10−3 cm2 V−1 second−1, respectively) may embody promising HTMs to yield good performance in PSCs. Therefore, the useful information obtained regarding control of the electron‐deficient π‐bridge units of MeTPA‐based HTMs is an effective way to obtain excellent HTMs for PSC applications.

Molecular Design Strategy in Developing Titanyl Phthalocyanines as Dopant-Free Hole-Transporting Materials for Perovskite Solar Cells: Peripheral or Nonperipheral Substituents?

We demonstrate a molecular design strategy to enhance the efficiency of phthalocyanine (Pc)-based hole-transporting materials (HTMs) in perovskite solar cells (PSCs). Herein, two titanyl phthalocyanine (TiOPc) derivatives are designed and applied as dopant-free HTMs in planar n-i-p-structured PSCs. The newly developed TiOPc compounds possess eight n-hexylthio groups attached to either peripheral (P-SC6-TiOPc) or nonperipheral (NP-SC6-TiOPc) positions of the Pc ring. Utilizing these dopant-free HTMs in PSCs with a mixed cation perovskite as the light-absorbing material and tin oxide (SnO2) as the electron-transporting material (ETM) results in a considerably enhanced efficiency for NP-SC6-TiOPc-based devices compared to PSCs using P-SC6-TiOPc. Hence, all of the photovoltaic parameters, including power conversion efficiency (PCE), fill factor, open-circuit voltage, and short-circuit current density, are remarkably improved from 5.33 ± 1.01%, 33.34 ± 3.45%, 0.92 ± 0.18 V, and 17.33 ± 2.08 mA cm-2 to 15.83 ± 0.44%, 69.03 ± 1.59%, 1.05 ± 0.01 V, and 21.80 ± 0.36 mA cm-2, respectively, when using the nonperipheral-substituted TiOPc derivative as the HTM in a PSC. Experimental and computational analysis suggests more compact molecular packing for NP-SC6-TiOPc than P-SC6-TiOPc in the solid state due to stronger π-π interactions, leading to thin films with better quality and higher performance in hole extraction and transportation. PSCs with NP-SC6-TiOPc also offer much higher long-term stability than P-SC6-TiOPc-based devices under ambient conditions with a relative humidity of 75%.

Application of a Tetra‐TPD‐Type Hole‐Transporting Material Fused by a Tröger's Base Core in Perovskite Solar Cells

One of the obstacles to the commercialization of perovskite solar cells (PSCs) is the high price and morphological instability of the most common hole‐transporting material (HTM) Spiro‐OMeTAD. Herein, a novel HTM, termed V1160, based on four N,N′‐bis(3‐methylphenyl)‐N,N′‐diphenylbenzidine (TPD)‐type fragments, fused by a Tröger's base core, is synthesized and successfully applied in PSCs. Investigation of the optical, thermal, and photoelectrical properties shows that V1160 is a suitable candidate for application as an HTM in PSCs. A promising power conversion efficiency (PCE) of over 18% is demonstrated, which is only slightly lower than that of Spiro‐OMeTAD. Moreover, V1160‐based devices exhibit improved performances in dopant‐free configurations and superior stability. Favorable morphological properties in combination with a simple synthesis make V1160 and related materials promising for HTM applications.

Structural effect on the thermodynamic and electrochemical properties of pyrene-based hole transport materials

We introduce six di-methoxyphenylamine-substituted pyrene arylamine derivatives as new hole transport materials (HTMs) by changing the position of OMe substituent on the phenylamine group and compare with three other derivatives denoted as N,N-di-p-methoxyphenyl-amine-substituted pyrene arylamine (para-PyA, -PyB, and -PyC) as references. The electronic, absorption and emission spectra, and transport properties of the new materials are investigated via density functional theory (DFT) calculations in combination with the Marcus hopping model. The stability and solubility of all the derivatives along with the parameters affecting the open circuit voltage (Voc), fill factor (FF), and short-circuit current density (Jsc) of the corresponding solar cells are obtained and discussed. We also examine the oxidation forms (+1 and +2) of structures to find the reasons for instability and reduction in efficiency of the device after the formation of the oxidized forms of HTMs. The results show that among the nine structures studied, the ortho-PyB derivative with CH3NH3PbI3 absorber and ortho-PyA derivative with (FAPbI3)0.85(CH3NH3PbBr3)0.15 absorber are promising HTMs for perovskite solar cells (PSCs) because they have larger Stokes shifts, appropriate highest occupied molecular orbital (HOMO) level, more stability, and acceptable hole mobility.