Doping of hole transporting materials typically increases the efficiency of perovskite solar cells but remains questionable for overall device stability.

The emerging CsPbI3 perovskites are highly efficient and thermally stable materials for wide‐band gap perovskite solar cells (PSCs), but the doped hole transport materials (HTMs) accelerate the undesirable phase transition of CsPbI3 in ambient. Herein, a dopant‐free D‐π‐A type HTM named CI‐TTIN‐2F has been developed which overcomes this problem. The suitable optoelectronic properties and energy‐level alignment endow CI‐TTIN‐2F with excellent charge collection properties. Moreover, CI‐TTIN‐2F provides multisite defect‐healing effects on the defective sites of CsPbI3 surface. Inorganic CsPbI3 PSCs with CI‐TTIN‐2F HTM feature high efficiencies up to 15.9 %, along with 86 % efficiency retention after 1000 h under ambient conditions. Inorganic perovskite solar modules were also fabricated that exhibiting an efficiency of 11.0 % with a record area of 27 cm2. This work confirms that using efficient dopant‐free HTMs is an attractive strategy to stabilize inorganic PSCs for their future scale‐up.

Three donor–π‐bridge–acceptor (D–π–A)‐type organic small molecules coded CI‐B1, CI‐B2, and CI‐B3 are designed, synthesized, and used as dopant‐free hole transporting materials (HTMs) for perovskite solar cells (PSCs). The strong electron‐donating triazatruxene central core (D), terthiophene conjugated arms (π), and three different strong electron‐accepting units (A) provide high intramolecular charge transfer nature and eliminate the need of dopants during the fabrication of PSCs. HTMs are investigated to understand the effect of terminal functional groups on the PSC performance. Interestingly, due to the change of end‐capping, three different organizations of self‐assembly with π–π stacking are observed in the solid thin films. Dopant‐free CI‐B1, CI‐B2, CI‐B3, and spiro‐OMeTAD with dopants are used with triple cation perovskite composition Cs0.1(MA0.15FA0.85)0.9Pb(I0.85Br0.15)3 (MA: CH3NH3+, FA: NHCHNH3+) in n‐i‐p architecture. The cells prepared with CI‐B3 not only exhibits a comparable power conversion efficiency (PCE) of 17.54% to the state‐of‐art of spiro‐OMeTAD with dopants (18.02%), but also demonstrates improved long‐term stability, maintaining 88% of its original PCE after 1000 h of illumination. The superior photovoltaic performance, synthetic simplicity, dopant‐free nature, high durability, and edge‐on molecular orientation of CI‐B3 show its great promise as a HTM candidate for efficient and stable PSCs.

Two structural isomers of carbazole decorated with triarylamine have been designed and synthesized with a facile synthetic procedure. The impact of triarylamine substitution on the isomeric structural linkage of carbazole on the optical, thermal, electrochemical, and photovoltaic properties has been extensively studied by combining experimental and simulation methods. Car­[2,3] showed a red shift in the absorption maximum compared to that of Car­[1,3], indicating the linear conjugation along the 2,7-position of carbazole in the former. The high thermal decomposition temperature (>420 °C) of these compounds could be attributed to the rigid structure of the carbazole core. Perovskite solar cells fabricated with Car­[2,3] as the hole transporting material (HTM) displayed the highest power conversion efficiency (PCE) of 19.23%. It can be attributed to the suitable energy alignment of the highest occupied molecular orbital (HOMO) of HTM with the adjacent perovskite valence band energy level, which results in efficient hole transport. Furthermore, the molecular dynamic simulation demonstrates that the triphenylamine substitution on the 2,3,6,7 positions of Car­[2,3] results in a more planar molecular alignment on top of the perovskite surface, promoting an efficient hole extraction. Essentially, when Car­[1,3] and Car­[2,3] were applied in perovskite solar cells, they showed enhanced long-term stability by retaining >80% of their initial PCEs after 1000 h of continuous illumination.

alternative to the existing conventional energy sources. [1] Organometal-halide perovskites show exceptional panchromatic light harvesting ability, high molar extinction coefficient, high charge carrier mobilities, and long electron-hole diffusion lengths. Further, the versatility and tunable electronic properties of perovskites are beneficial for realizing higher photovoltaic performance reaching over 25%. [2][3][4][5] However, low charge extraction and poor stability of the metal-halide perovskite limit their credentials in large-scale applications.To overcome these limitations, p-type semiconducting materials, also known as hole-transporting materials (HTMs), were sandwiched between perovskite and metal electrode. HTMs play a vital role in PSCs to extract and transfer the positive charges and thus achieve high efficiency. [6][7][8][9][10] They can be classified as inorganic, [11] polymeric, [12] and small molecular organic HTMs. [13,14] Among them, small molecular HTMs are superior to other counterparts owing to their structural diversity, well-defined molecular Triarylamine-substituted bithiophene (BT-4D), terthiophene (TT-4D), and quarterthiophene (QT-4D) small molecules are synthesized and used as low-cost hole-transporting materials (HTMs) for perovskite solar cells (PSCs). The optoelectronic, electrochemical, and thermal properties of the compounds are investigated systematically. The BT-4D, TT-4D, and QT-4D compounds exhibit thermal decomposition temperature over 400 °C. The n-i-p configured perovskite solar cells (PSCs) fabricated with BT-4D as HTM show the maximum power conversion efficiency (PCE) of 19.34% owing to its better hole-extracting properties and film formation compared to TT-4D and QT-4D, which exhibit PCE of 17% and 16%, respectively. Importantly, PSCs using BT-4D demonstrate exceptional stability by retaining 98% of its initial PCE after 1186 h of continuous 1 sun illumination. The remarkable long-term stability and facile synthetic procedure of BT-4D show a great promise for efficient, stable, and low-cost HTMs for PSCs for commercial applications.

Three novel donor–π‐bridge–donor (D‐π‐D) hole‐transporting materials (HTMs) featuring triazatruxene electron‐donating units bridged by different 3,4‐ethylenedioxythiophene (EDOT) π‐conjugated linkers have been synthesized, characterized, and implemented in mesoporous perovskite solar cells (PSCs). The optoelectronic properties of the new dumbbell‐shaped derivatives (DTTXs) are highly influenced by the chemical structure of the EDOT‐based linker. Red‐shifted absorption and emission and a stronger donor ability were observed in passing from DTTX‐1 to DTTX‐2 due to the extended π‐conjugation. DTTX‐3 featured an intramolecular charge transfer between the external triazatruxene units and the azomethine–EDOT central scaffold, resulting in a more pronounced redshift. The three new derivatives have been tested in combination with the state‐of‐the‐art triple‐cation perovskite [(FAPbI3)0.87(MAPbBr3)0.13]0.92[CsPbI3]0.08 in standard mesoporous PSCs. Remarkable power conversion efficiencies of 17.48 % and 18.30 % were measured for DTTX‐1 and DTTX‐2, respectively, close to that measured for the benchmarking HTM spiro‐OMeTAD (18.92 %), under 100 mA cm−2 AM 1.5G solar illumination. PSCs with DTTX‐3 reached a PCE value of 12.68 %, which is attributed to the poorer film formation in comparison to DTTX‐1 and DTTX‐2. These PCE values are in perfect agreement with the conductivity and hole mobility values determined for the new compounds and spiro‐OMeTAD. Steady‐state photoluminescence further confirmed the potential of DTTX‐1 and DTTX‐2 for hole‐transport applications as an alternative to spiro‐OMeTAD.

Three benzodipyrrole (BDP)‐based organic small molecules with substituted 4‐methoxyphenyl (CB‐1), 3‐fluorophenyl (CB‐2), and 3‐trifluoromethylphenyl (CB‐3) are designed, synthesized, and used as a hole‐transporting material (HTM) for perovskite solar cells (PSCs). The electrochemical, optical, thermal, electronic, and optoelectronic properties of the HTMs are characterized to verify their suitability for PSCs. The terminal functional groups of the HTMs having different heteroatoms mainly target effective defect passivation of perovskites. Photoluminescence studies and molecular dynamic simulations reveal that fluorine atoms within CB‐2 and CB‐3 can contribute to the defect passivation via interaction with Pb of the perovskite. In particular, a highly planar conformation of CB‐2 on the perovskite surface can facilitate more efficient hole transfer at the interface. Thus, the PSCs employing CB‐2 achieve the highest power conversion efficiency (PCE) of 18.23% while the devices using CB‐1 and CB‐3 exhibit a lower PCE of 16.78% and 16.74%, respectively. PSCs with the BDP‐based HTMs demonstrate excellent long‐term storage stability without degradation in their PCEs over 6 months. The highly planar geometry, defect passivation effect, and hydrophobicity of CB‐2 show its great potential as an HTM for efficient and stable PSCs.

Defects of metal-halide perovskites detrimentally influence the optoelectronic properties of the thin film and, ultimately, the photovoltaic performance of perovskite solar cells (PSCs). Especially, defect-mediated nonradiative recombination that occurs at the perovskite interface significantly limits the power conversion efficiency (PCE) of PSCs. In this regard, interfacial engineering or surface treatment of perovskites has become a viable strategy for reducing the density of surface defects, thereby improving the PCE of PSCs. Here, an organic molecule, tris(5-((tetrahydro-2H-pyran-2yl)oxy)pentyl)phosphine oxide (THPPO), is synthesized and introduced as a defect passivation agent in PSCs. The PO terminal group of THPPO, a Lewis base, can passivate perovskite surface defects such as undercoordinated Pb2+. Consequently, improvement of PCEs from 19.87 to 20.70% and from 5.84 to 13.31% are achieved in n−i−p PSCs and hole-transporting layer (HTL)-free PSCs, respectively.