Hole-transporting Materials For Perovskite Solar Cells Research Articles

Triselenasumanene-based organic molecules as donor and hole-transporting materials for next-generation solar cells

The optoelectronic and charge transport properties of triselenasumanene-based organic molecules were studied using electronic structure calculations to explore their potential as a hole-transporting material (HTM) in perovskite solar cells (PSCs) and as electron donors in organic solar cells (OSCs). Based on the recently synthesized triselenasumanene (SESUM) molecule, nine molecules (SESUMXn, where X = anthracene (A), tetracene (T) and pentacene (P), n = number of attached A, T and P, i.e. 1, 2 and 3) were designed by extending the π-conjugation. The newly designed molecules possessed suitable energy-level alignment with the energy bands of commonly used perovskite material, CH3NH3PbI3, in PSCs, and are suitable as electron-donor material with the commonly used acceptor material, PC61BM, in OSCs. The calculated ionic state properties and electrophilicity index also showed that the studied molecules were potential donor materials for OSCs. Further, the calculated open circuit voltage and fill factor of SESUM and anthracene- and tetracene-substituted SESUM molecules were comparable with those of recently reported donor molecules. The calculated absorption spectra, effective hole transfer integral and stacking angle distribution showed the suitability of SESUMX2 and SESUMX3 molecules as HTM in PSCs. The results of periodic density functional theory calculations showed that the tri-substituted SESUM molecules, SESUMX3 (where, X = A, T and P), were effectively adsorbed on the CH3NH3PbI3 surface and abstracted the hole carrier from the perovskite surface.

Rational Design of New Small Derivatives of 2,2'-Bithiophene as Hole Transport Material for Perovskite Solar Cells.

Using Density Functional Theory (DFT) and Time Dependent DFT (TD-DFT) methods, this inquiry theoretically examines seven novel hole-transport materials (HTMs) namely DFBT1, DFBT2, DFBT3, DFBT4, DFBT5, DFBT6, and DFBT7 based on the 2,2'bithiophene core for future use as HTMs for perovskite solar cells (PSCs). The model molecule has been modified through substituting the end groups situated on the diphenylamine moieties with a tow acceptor bridged by thiophene, this modification was performed to test the impact of the π-bridge and acceptor on the electronic, photophysical, and photovoltaic properties of the newly created molecules. DFBT1 - DFBT7 displayed a lower band gap (1.49 eV to 2.69 eV) than the model molecule (3.63 eV). Additionally, the newly engineered molecules presented a greater λmax ranging from 393.07 nm to 541.02 nm in dimethylformamide solvent, as compared to the model molecule (380.61 nm). The PCEs of all newly designed molecules (22.42% to 29.21%) were high compared with the reference molecule (19.62%). Thus, this study showed that all seven newly small molecules were excellent candidates for a novel PSC.

Theoretical study of optoelectronic performance of hole-transporting material quinoxaline-based with architecture (D-A-D) in perovskite solar cells: A DFT method

Developing ideal small-molecule hole-transporting materials (HTMs) is one of the most effective methods to improve the performance of perovskite solar cells (PSCs). Meanwhile, designing new molecules with theoretical chemistry methods and gaining a more fundamental understanding of the structure-property relationship is significant for developing highly efficient HTMs. In this study, new HTMs were designed based on quinoxaline core. Based on time-dependent density functional theory (TD-DFT) and density functional theory (DFT), the electron transfer mechanism was investigated by hole and electron analysis and inter-fragment charge transfer (IFCT). The results show that HTMs (TQ2, TQ3, TQ5, TQ7, and TQ8) exhibit suitable energy levels. The matched energy levels with MAPbI3 are helpful for the interfacial charge transfer. IFCT and hole-electron distribution indices show that TQ5 has a higher centroid distance (D = 1.74 Å), a greater degree of spatial expansion (H = 4.58 Å), the smaller overlap area (Sr = 0.62), the highest degree separation (t = −0.11 Å), more transmission of net charge (Q = 0.60 e−), and the highest hole contribution (71.38 %). Due to matched energy levels with MAPbI3, superior hole-electron distribution indices, good solubility, and better hole mobility, it is suggested that TQ5 has desirable properties as HTM in perovskite solar cells with (n-i-p) architecture.

Exploring Acceptor Modification in Helicene‐Phenylamine‐Based Small Molecules for Organic and Perovskite Solar Cells

The current quantum mechanical study is focused on the fabrication of eight helicene‐phenylamine‐based molecules (MPAM1–MPAM8) to investigate their photovoltaic (PV) and optoelectronic properties for photovoltaic cells (PVCs). The outcomes revealed that fabricated chromophores showed deeper highest occupied molecular orbital levels, higher solubility, low exciton binding energy, greater hole mobility with low band gap energy than the model compound (MPAR). Moreover, the reorganization energy values interpret that newly fabricated compounds possess high charge mobility compared to the representative molecule (MPAR) which encourages their usage as HTM in PSCs. All the freshly designed molecules revealed greater estimated open circuit voltage values contrasted to the reference molecule (MPAR) which ensures their prominent working efficacy. The results signify the competence of this strategic approach, paving a new path for the fabrication of hole transport material (HTM) for perovskite solar cells (PSCs) and donor molecules for organic solar cells (OSCs).

Improving the Conductivity of Amide-Based Small Molecules through Enhanced Molecular Packing and Their Application as Hole Transport Mediators in Perovskite Solar Cells.

Organic-inorganic hybrid halide perovskite solar cells (PSCs) have attracted substantial attention from the photovoltaic research community, with the power conversion efficiency (PCE) already exceeding 26%. Current state-of-the-art devices rely on Spiro-OMeTAD as the hole-transporting material (HTM); however, Spiro-OMeTAD is costly due to its complicated synthesis and expensive product purification, while its low conductivity ultimately limits the achievable device efficiency. In this work, we build upon our recently introduced family of low-cost amide-based small molecules and introduce a molecule (termed TPABT) that results in high conductivity values (∼10-5 S cm-1 upon addition of standard ionic additives), outperforming our previous amide-based material (EDOT-Amide-TPA, ∼10-6 S cm-1) while only costing an estimated $5/g. We ascribe the increased optoelectronic properties to favorable molecular packing, as shown by single-crystal X-ray diffraction, which results in close spacing between the triphenylamine blocks. This, in turn, results in a short hole-hopping distance between molecules and therefore good mobility and conductivity. In addition, TPABT exhibits a higher bandgap and is as a result more transparent in the visible range of the solar spectrum, leading to lower parasitic absorption losses than Spiro-OMeTAD, and has increased moisture stability. We applied the molecule in perovskite solar cells and obtained good efficiency values in the ∼15% range. Our approach shows that engineering better molecular packing may be the key to developing high-efficiency, low-cost HTMs for perovskite solar cells.

Ladder-type dihydronaphtho[1,2,3,4-rst]pentaphene as building block to construct hole-transporting materials for perovskite solar cells

The stability and photovoltaic performance of perovskite solar cells (PSCs) are greatly affected by the use of hole-transporting materials (HTMs). Polycyclic aromatic hydrocarbons (PAHs) are known for their planar structures, which facilitate efficient charge transport and intermolecular interactions, resulting they possess unique electronic and optical properties. In this study, we describe the synthesis of three D‒π‒D type PAHs-based HTMs compounds (DC-1, DC-2, and DC-3) that contain dihydronaphtho[1,2,3,4-rst]pentaphene (DHNP) as a π conjugation bridge, p-methoxy group-substituted arylamine, and diphenylamine-substituted carbazole groups as the donor groups. These DHNP-based molecules can be used as hole-transporting materials in PSCs due to their favorable frontier molecular orbitals (HOMO/LUMO) energy levels. The PSC devices fabricated with DC-1 yielded a highly efficient power conversion efficiency (PCE) of 18.09%, outperforming those based on DC-2 (13.21%) and DC-3 (14.91%), and slightly higher than those using control spiro-OMeTAD (16.93%). The proposed novel D‒π‒D molecules demonstrate potential as HTMs with promising performance for PSCs and contribute to the development of high-efficiency perovskite solar cells.

Fluorinated Pentafulvalene‐Fused Hole‐Transporting Material Enhances the Performance of Perovskite Solar Cells with Efficiency Exceeding 23%

AbstractOrganic small molecular materials with coplanar π‐conjugated system as HTMs in perovskite solar cells (PSCs) have attracted considerable attention due to their high charge transport capability and thermal stability. Herein, three novel pentafulvalene‐fused derivatives with or without fluorine atoms incorporated (YSH‐oF and YSH‐mF and YSH‐H, respectively) are designed, synthesized, and applied as hole‐transporting materials (HTMs) in PSCs fabrication. The fluorinated HTMs, YSH‐oF and YSH‐mF, exhibited higher hole mobility and better charge extraction at the perovskite/HTM interface than non‐fluorinated one do, presumably due to the closer intermolecular π–π packing interactions. As a result, small‐area (0.09 cm2) PSCs made with YSH‐oF and YSH‐mF achieved an impressive power conversion efficiency (PCE) of 23.59% and 22.76% respectively, with negligible hysteresis, in contrast with the 20.57% for the YSH‐H‐based devices. Furthermore, for large‐area (1.00 cm2) devices, the PSCs employing YSH‐oF exhibited a PCE of 21.92%. Moreover, excellent long‐term device stability is demonstrated for PSCs with F‐substituted HTMs (YSH‐oF and YSH‐mF), presumably due to the higher hydrophobicity. This study shows the great potential of fluorinated pentafulvalene‐fused materials as low‐cost HTM for efficient and stable PSCs.

Slot-Die Coated Copper Indium Disulfide as Hole-Transport Material for Perovskite Solar Cells

Perovskite photovoltaics have the potential to significantly lower the cost of producing solar energy. However, this depends on the ability of the perovskite thin film and other layers in the solar cell to be deposited using large-scale techniques such as slot-die coating without sacrificing efficiency. In perovskite solar cells (PSCs), Spiro-OMeTAD, a small molecule-based organic semiconductor, is commonly used as the benchmark hole transport material (HTL). Despite its effective performance, the multi-step synthesis of Spiro-OMeTAD is complex and expensive, making large-scale printing difficult. Copper indium disulfide (CIS) was chosen in this study as an alternative inorganic HTL for perovskite solar cells due to its ease of fabrication, cost-effectiveness, and improvements to the economic feasibility of cell production. In this study, all layers of perovskite solar cell were printed and compared to a spin-coating-based device. Various parameters affecting the layer quality and thickness were then analyzed, including substrate temperature, print head temperature, printing speed, meniscus height, shim thickness, and ink injection flow rate. The small print area achieved spin-coating quality, which bodes well for large-scale printing. The printed cell efficiencies were comparable to the reference cell, having a 9.9% and 11.36% efficiency, respectively.

Designing Donor‐Acceptor‐Donor (D‐A‐D) Type Molecules for Efficient Hole‐Transporting in Perovskite Solar Cells – A DFT Study

AbstractWe designed eight hole‐transporting materials (HTMs) of D‐A‐D type comprising an acceptor (A) unit flanked between two triphenylamine (TPA) donor (D) units. The structural, electronic, and absorption properties of designed molecules are studied using density functional theory (DFT) and time‐dependent DFT (TD‐DFT) methods. The MPW1PW91 functional with a 6‐31g(d,p) basis set was chosen, followed by a careful benchmark of DFT functionals. We identified dibenzothiophene‐triphenylamine (DBT‐TPA) and dibenzo‐1,4‐dioxaspiro[4,4]nonane‐triphenylamine (DBDN‐TPA) as the most promising molecules due to their unique properties, such as finite π‐conjugation, suitable highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), deep blue absorption, and lower reorganization energy than the recently reported anthradithiophene–triphenylamine (ADT‐TPA) based HTMs. Furthermore, the newly proposed D‐(L‐A‐L)‐D type molecules with a linker (L) display the enhanced features required for improved hole mobility. Our work demonstrates the fine‐tuning of electronic interactions between the donor and acceptor units, with a linker (L), in achieving the planarity, absorption, and hole mobility essential for efficient HTMs in perovskite solar cells.

The Future of Spirobifluorene‐Based Molecules as Hole‐Transporting Materials for Solar Cells

Organic–inorganic halide perovskite solar cells (PSCs) and organic solar cells (OSCs) attract great attention as alternative renewable photovoltaic technology. The state‐of‐the‐art spiro‐OMeTAD (2,2′,7,7′‐tetrakis‐(N,N‐di‐p‐methoxyphenylamine)‐9,9′‐spirobifluorene) is the most successful hole‐transport material (HTM) employed in PSCs, whereas solution‐processed inverted OSCs generally use poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). Recently, various types of spirobifluorene‐based organic small molecules are reported to overcome the known disadvantages of spiro‐OMeTAD, such as the complex synthetic route, high synthetic cost, and requirement for hygroscopic dopants to improve the charge‐carrier mobility and device performance. Examples of spirobifluorene‐based molecules are also reported as alternative HTMs in inverted OSCs to exceed the drawbacks of PEDOT:PSS, such as acidity and batch‐to‐batch reproducibility. These features significantly limit spiro‐OMeTAD and PEDOT:PSS for large‐scale application in the future. Herein, an overview of recent developments in spirobifluorene organic small molecules as HTM in PSCs and OSCs is provided by focusing on synthetic and electrical features. Finally, the further research directions are discussed to develop novel spirobifluorene‐based HTMs for the realization of reliable and long‐term stable photovoltaic devices.

Graphene quantum dots (GQD) and edge-functionalized GQDs as hole transport materials in perovskite solar cells for producing renewable energy: a DFT and TD-DFT study.

This study investigated the potential suitability of graphene quantum dots (GQD) and certain edge-functionalized GQDs (GQD-3Xs) as hole transport materials (HTMs) in perovskite solar cells (PSCs). The criteria for appropriate HTMs were evaluated, including solubility, hole mobility, light harvesting efficiency (LHE), exciton binding energy (Eb), hole reorganization energy (λh), hole mobility, and HTM performance. It was found that several of the compounds had higher hole mobility than Spiro-OMeTAD, a commonly used HTM in PSCs. The open circuit voltage and fill factor of the suitable GQD and GQD-3Xs were found to be within appropriate ranges for HTM performance in MAPbI3 PSCs. GQD-COOH and GQD-COOCH3 were identified as the most suitable HTMs due to their high solubility, small λh, and appropriate performance.

Effects of Overnight Oxidation on Perovskite Solar Cells with Co(III)TFSI Co-Doped Spiro-OMeTAD

Metal-halide perovskite solar cells (PSCs) have achieved remarkable power conversion efficiencies in recent years, and spiro-OMeTAD plays a significant role as a hole transport material in PSCs with record efficiencies. However, further studies and systematic experimental procedures on doped spiro-OMeTAD are required to enable a reliable process for potential commercialization. In particular, the effect of the prolonged oxidation of Co(III)TFSI co-doped spiro-OMeTAD has been one of the unanswered topics in PSC research. In this work, we investigate the influence of overnight oxidation on the performance of PSCs with Co(III)TFSI co-doped spiro-OMeTAD. Co-doping spiro-OMeTAD with Co(III) complexes instantly oxidizes spiro-OMeTAD, leading to an improvement in power conversion efficiency (PCE) from 13.1% (LiTFSI-doped spiro-OMeTAD) to 17.6% (LiTFSI + Co(III)TFSI-doped spiro-OMeTAD). It is found that PSCs with spiro-OMeTAD co-doped with Co(III)TFSI without overnight oxidation could retain around 90% of the efficiency under maximum power point tracking at 1-sun illumination for 3000 min, whereas the efficiencies drop by more than 30% when Co(III)TFSI co-doped spiro-OMeTAD is exposed to overnight oxidation. Hence, it is important to inhibit the unnecessary overnight oxidation of Co(III)TFSI co-doped spiro-OMeTAD so as to save excess fabrication time and overcome the poor stability issues.

Facile synthesis of spiro-core-based hole-transporting material for high-performance and stable perovskite solar cells

Two new spirocore-based hole-transporting materials (HTMs), spiro-1 and spiro-2, with 5H-spiro(benzo[1,2-b:6,5-b']dithiophene-4,4′-cyclopenta[2,1-b:3,4-b′]dithiophen)-5-one moiety connected with multiple triphenylamine donor substituents are synthesized via two-step synthesis with low cost and simple procedures and used as HTM in perovskite solar cells (PSCs). The correlation between different HTM structures and the performance of the PSCs was investigated systematically. Experiments results on the thermal stability, photophysical, electrochemical, charge-transporting, as well as film-forming properties show that spiro-1 and spiro-2 are suitable candidate as HTMs for PSCs. The fabricated PSCs with spiro-1 and spiro-2 as HTMs achieved an excellent power conversion efficiency (PCE) of 21.67 % and 19.65 % respectively, both with negligible hysteresis. The obtained PCE of 21.67 % based on spiro-1 is higher than that of the reference solar cell using traditional HTM of spiroOMeTAD (20.59 %) under the same conditions. It may be ascribed to the higher hole mobility, the more efficient hole extraction at the HTM/perovskite interface, the better film morphology. Moreover, the devices based on the new HTM showed good long-term stability and maintained over 80 % of their initial efficiency under continuous stressing at 85 °C and light illumination at 50 °C for 500 h in air without any encapsulation, which were superior to that of spiroOMeTAD. This work demonstrates that the newly developed spirofused molecules are promising HTMs for highly efficient and stable PSCs for the future commercialization of PSCs.

Solution-Processed Ternary Tin (II) Alloy as Hole-Transport Layer of Sn-Pb Perovskite Solar Cells for Enhanced Efficiency and Stability.

Tin-lead (Sn-Pb) narrow-bandgap (NBG) perovskites show great potential in both single-junction and all-perovskite tandem solar cells. Sn-Pb perovskite solar cells (PSCs) are still limited by low charge collection efficiency and poor stability. Here, a ternary Sn (II) alloy of SnOCl is reported as the hole-transport material (HTM) with a work function of 4.95eV for Sn-Pb PSCs. The solution-processed SnOCl layer has a texture structure that not only reduces the optical loss of the devices, but also changes grain growth of Sn-Pb perovskites and boosts the carrier diffusion length to 3.63µm. The formation of small perovskite grains at the HTM/perovskite interface is suppressed. These result in an almost constant internal quantum efficiency (IQE) of 96 ± 2% across the absorption spectrum of Sn-Pb perovskites. The SnOCl HTM significantly enhances the stability of Sn-Pb PSCs with 87% of its initial efficiency retained after 1-sun illumination for 1200h, and keeps 85% efficiency under 85°C thermal stress for 1500h. The hybrid HTM further improves the stabilized efficiencies of single-junction Sn-Pb PSCs and all-perovskite tandem solar cells to 23.2% and 25.9%, respectively. This discovery opens an avenue to the multicomponent metal alloys as HTM in PSCs.

Guidelines for Fabricating Highly Efficient Perovskite Solar Cells with Cu2O as the Hole Transport Material.

Organic hole transport materials (HTMs) have been frequently used to achieve high power conversion efficiencies (PCEs) in regular perovskite solar cells (PSCs). However, organic HTMs or their ingredients are costly and time-consuming to manufacture. Therefore, one of the hottest research topics in this area has been the quest for an efficient and economical inorganic HTM in PSCs. To promote efficient charge extraction and, hence, improve overall efficiency, it is crucial to look into the desirable properties of inorganic HTMs. In this context, a simulation investigation using a solar cell capacitance simulator (SCAPS) was carried out on the performance of regular PSCs using inorganic HTMs. Several inorganic HTMs, such as nickel oxide (NiO), cuprous oxide (Cu2O), copper iodide (CuI), and cuprous thiocyanate (CuSCN), were incorporated in PSCs to explore matching HTMs that could add to the improvement in PCE. The simulation results revealed that Cu2O stood out as the best alternative, with electron affinity, hole mobility, and acceptor density around 3.2 eV, 60 cm2V−1s−1, and 1018 cm−3, respectively. Additionally, the results showed that a back electrode with high work-function was required to establish a reduced barrier Ohmic and Schottky contact, which resulted in efficient charge collection. In the simulation findings, Cu2O-based PSCs with an efficiency of more than 25% under optimal conditions were identified as the best alternative for other counterparts. This research offers guidelines for constructing highly efficient PSCs with inorganic HTMs.

Zn(II) and Cu(II) tetrakis(diarylamine)phthalocyanines as hole-transporting materials for perovskite solar cells

Finding new hole-transporting materials (HTMs) suitable for replacing the state-of-the-art spiro-OMeTAD is still challenging. In this work, newly synthesized diarylamine-substituted metal phthalocyanines (MPcs, M = Zn(II) or Cu(II)) functionalized with either linear or branched alkoxy chains are evaluated as HTMs in perovskite solar cells. Both the nature of the alkoxy chains and that of the coordinated metal species were found to influence the functional properties of the new MPcs. In particular, devices based on a ZnPc featuring four n-butoxy side chains exhibited the highest power conversion efficiencies (PCEs). A PCE of 20.00% was reached for triple cation perovskite devices, and a PCE up to 20.18% could be achieved for double cation devices.

Liquid crystal semiconductor C6TBTAPH2 for hole transport materials in pervoskite solar cells: Fabrication, characterization, and simulation

A study on efficient perovskite solar cells (PSCs) utilizing non-peripherally substituted octahexyltetrabenzotriazaporphyrin (C6TBTAPH2) hole transporting material (HTM) was demonstrated through fabrication, characterization, and simulation. C6TBTAPH2 semiconductor possesses a compatible energy band diagram (highest occupied molecular orbital energy levels of 5.17 eV and energy band gap of 1.59 eV) and a relatively high charge carrier mobility for a potential HTM in PSC. The simulated PSCs (using solar cell capacitance simulator – one dimensional programs) with C6TBTAPH2 HTMs exhibited the relatively high photovoltaic performance with power conversion efficiencies (PCEs) of 19.5%, but there existed a gap between the simulated and experimental data. Those differences were in part due to the low acceptor density of the pristine and/or p-type doped C6TBTAPH2 HTM and the parallel alignment of C6TBTAPH2 molecules on glass substrates. We suggest that C6TBTAPH2 semiconductor could be a potential HTM in PSC if the indications from the simulated results are well dealt with.

Dopant‐Free Phthalocyanine Hole Conductor with Thermal‐Induced Holistic Passivation for Stable Perovskite Solar Cells with 23% Efficiency

AbstractSimultaneous passivation of the defects at the surface and grain boundaries of perovskite films is crucial to achieve efficient and stable perovskite solar cells (PSCs). It is highly desirable to accomplish the above passivation through rational engineering of hole transport materials (HTMs) in combination with appropriate procedure optimization. Here, methylthiotriphenylamine‐substituted copper phthalocyanine (SMe‐TPA‐CuPc) is reported as a dopant‐free HTM for PSCs, exhibiting excellent efficiency, and stability. After thermal annealing, SMe‐TPA‐CuPc molecules diffused into the bulk of the perovskite film and effectively passivated the defects in the bulk and at the interface of the perovskite, owing to the strong interaction between the methylthio moiety and undercoordinated lead. The best‐performing annealed SMe‐TPA‐CuPc‐based device shows efficiency of 21.51%, which is higher than the unannealed SMe‐TPA‐CuPc‐based device (power‐conversion efficiency (PCE) of 20.75%) and reference doped spiro‐OMeTAD‐based device (PCE of 20.61%). Further modification of the perovskite of the annealed SMe‐TPA‐CuPc‐based device by the QAPyBF4 additive result in even higher efficiency of 23.0%. It also shows excellent stability, maintaining 96% of its initial efficiency after 3624 h aging at 85 °C. This work highlights the great potential of phthalocyanine‐based dopant‐free HTMs and the defect passivation by thermal‐induced molecular diffusion strategy for developing highly efficient and stable PSCs.

Analytical Review of Spiro‐OMeTAD Hole Transport Materials: Paths Toward Stable and Efficient Perovskite Solar Cells

The hole transport material (HTM) of organic–inorganic perovskite solar cells (PVSCs) plays a very important role for achieving high power conversion efficiency and long‐term stability. 2,2’,7,7’‐tetrakis[N,N‐di(4‐methoxyphenyl)amino]‐9‐9’‐spirobifluorene (spiro‐OMeTAD) is the first solid‐state HTM used in PVSCs and has gained tremendous attention during the last decade. Herein, the concept of spirolinkage for synthesis of spiro‐based HTMs is discussed, followed by an overview of the desirable optical and electrical properties of spiro‐OMeTAD. Recent progress in efficiency improvements of spiro‐based PVSCs is analyzed systematically, and the impacts of interface engineering, dopant‐free spiro‐OMeTAD, and novel spiro‐based HTMs are reviewed in detail. The hole mobility of spiro‐OMeTAD depends on the types of dopants and doping concentration. Commonly used lithium bis(trifluoromethylsulfonyl)imide and 4‐tert‐butylpyridine additives reduce the PVSC stability due to hygroscopicity and corrosiveness, respectively. The effects of additives on device stability and the techniques to improve the long‐term stability of spiro‐based PVSCs are also discussed. The review and analysis of various methods and strategies presented is useful for the perovskite research community, providing guidance and directions toward the further development of spiro‐based HTMs for PVSCs with improved efficiency and stability.

An asymmetrically substituted dithieno[3,2-b:2′,3′-d]pyrrole organic small-molecule hole-transporting material for high-performance perovskite solar cells

Hole-transporting materials play a vital role in terms of the performance of perovskite solar cells (PSCs). The dithieno[3,2- b :2′,3′- d ]pyrrole (DTP), an S,N-heterocyclic building block, has been proved to be desirable for molecular design of hole-transporting materials in PSCs. We developed an asymmetrically substituted DTP small-molecule (JW12) and a reference compound (JW11). The asymmetrical structure of JW12 leads to different absorption properties and electron distribution. The device in a planar n-i-p architecture using JW12 shows a much higher PCE (18.07%) than that based on JW11 (15.46%), which is also better than the device based on spiro-OMeTAD (17.47%). We hope our research can provide a new perspective in molecular design of organic HTMs for perovskite solar cells.