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Excess PbI2 has been deemed as indispensable component to boost the efficiency of perovskite solar cells (PSCs). However, the random aggregation of PbI2 crystals seriously disturbs the transport behavior of the carrier and accelerates the degradation of perovskite film. Herein, an effective strategy to in situ disperse excess PbI2 crystals via the columnar liquid crystal (T6TE) is developed. Rapid self‐assembly induced by intermolecular π–π interaction enables T6TE to form the ordered columnar phase with "edge‐on" orientation in perovskite. The columnar T6TE can efficiently disperse excess PbI2 crystals with the merits of strong negative electrostatic potential and highly steric hindrance. Target perovskite deserves preferable crystallization and reconstructed surface, leading to reduced defects density, less residual stress, and efficient carrier transport. Besides, the T6TE significantly impedes the degradation of perovskite film and the formation of Pb0 defects. Resultant T6TE‐assisted PSCs achieve the champion power conversion efficiency (PCE) of 24.27% for mixed Cs+‐FA+‐MA+ perovskite. The PCE of a larger area (1 cm2) device reaches to 21.50%. The unencapsulated device maintains ≈85% of the initial PCE after 1500 h storage in the atmosphere with 40–60% relative humidity. This work provides a new strategy to in situ disperse excess PbI2 by incorporating columnar liquid crystal for the first time. [ABSTRACT FROM AUTHOR]

α‐phase formamidine lead iodine (α‐FAPbI3) as a competitive candidate to pursue high‐performance perovskite solar cells (PSCs) suffers from the weakness of random nucleation and disordered growth in chasing high‐grade polycrystalline films. Here, single‐crystal seeds crystallization (SCSC) method is proposed to obtain high‐quality α‐FAPbI3 perovskite films for the first time. Six single‐crystals seeds (CsPbBr3, CsPbI3, FAPbBr3, FAPbI3, MAPbBr3, and MAPbI3) are employed to regulate α‐FAPbI3 perovskite crystallization. These seeds act as nucleation sites and allow the perovskite to grow directly. The rapid crystallization significantly improves the crystallinity of perovskite films with uniform morphology, large grain size, and less defects. Of particular note, FAPbBr3 seed prefers to grow α‐FAPbI3 epitaxially from FAPbBr3@PbI2 heterostructure through a halogen anion exchange process. The average grain size of FAPbBr3‐perovskite film is boosted to 2.6 µm, and the trap density reduced by 11 times. The resultant FAPbBr3‐PSCs achieve a maximum power conversion efficiency (PCE) of 23.84% with a high open‐circuit voltage of 1.18 V. The unencapsulated PSC retains 91% of the initial PCE after 3000 h of storage at ≈30–50% relative humidity and preserves 98.5% of the original value after 155 h illumination with maximum power point tracking. [ABSTRACT FROM AUTHOR]

The absent photo‐response in near‐infrared (NIR) light (>800 nm) of lead‐based perovskite solar cells (PSCs) limits the further improvement of their power conversion efficiency (PCE). Here, a narrow bandgap p‐type phthalocyanine derivative (Copper(II) 2,3,9,10,16,17,23,24‐octakis((4‐(bis(4‐methoxyphenyl)amino)phenyl)ethynyl)phthalocyanine –8TPAEPC) with NIR absorption is synthesized to extend the photovoltaic response of perovskite to 850 nm. After doping the 8TPAEPC into the perovskite photoactive layer, the perovskite crystal quality is improved, resulting in its good electrical conductivity and less surface defects. Furthermore, the molecules stacking on the grain boundaries construct the charge transportation paths, as well as the p–n bulk heterojunction with enhanced built‐in potential. The target PSCs are optimized with notably enhanced PCE from 20% up to 22.10%, and excellent stability that is over 80% of the initial level at 70–80% relative humidity can be maintained for more than 500 h, benefiting from the improved hydrophobicity of 8TPAEPC. In addition, 8TPAEPC also serves as a dopant‐free, highly carrier‐mobile, and moreover, NIR‐responsive hole transport layer (HTL) with boosted PCE of 20.42% that reaches state of the art level among the dopant‐free metal phthalocyanines HTL‐based PSCs. [ABSTRACT FROM AUTHOR]

A star-shaped hole-transporting material (HTM) using the triphenylamine (TPA) as the core named TP1 is designed and synthesized. The implementation of the new HTM in CH3NH3PbI3-based perovskite solar cells exhibits an excellent overall power conversion efficiency (PCE) of 12.63 % without the use of any dopants and additives, which is comparable to the 14.93 % obtained using p-doped spiro-OMeTAD. Importantly, the devices based on TP1 show relatively stable device performance compared to spiro-OMeTAD after aging in ambient air with 30 % relative humidity without encapsulation in the dark. The present results demonstrate that TPA could be an excellent building block to design dopant-free HTMs for perovskite solar cells and holds promise to replace p-doped spiro-OMeTAD, which is important for the fabrication of cost-effective and stable devices. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) possess both high‐power conversion efficiency (PCE) and good operation stability for future application. Although many different types of hole‐transporting materials (HTMs) are assessed, few dopant‐free small organic molecule HTMs‐based PSC cells exist, which exhibit excellent stability under both heat and illumination. Herein, two novel HTMs that are based on 9‐(4‐methoxyphenyl) carbazole and benzodithiophene cores are synthesized and named N1,N1′‐(9‐(4‐methoxyphenyl)‐9H‐carbazole‐3,6‐diyl)bis(N1‐(4‐(bis(4‐methoxyphenyl)amino)phenyl)‐N4,N4‐bis(4‐methoxyphenyl)benzene‐1,4‐diamine) (PhCz‐4MeOTPA) and N1,N1′‐(benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl)bis(N1‐(4‐(bis(4‐methoxyphenyl)amino)phenyl)‐N4,N4‐bis(4‐methixyphenyl)benzene‐1,4‐diamine) (BDT‐4MeOTPA). Of the two HTMs, PhCz‐4MeOTPA possesses a lower level of planarity than that of BDT‐4MeOTPA, which inhibits molecular stacking to improve film quality and increases hole‐transport mobility and charge transport. A PCE of 16.04% is achieved with the application of dopant‐free PhCz‐4MeOTPA in PSCs, which is higher than that of dopant‐free BDT‐4MeOTPA. The unencapsulated PSC devices based on PhCz‐4MeOTPA maintain 82% of their initial values under continuous sun illumination in an ambient environment at 40–45 °C after 672 h and 92% of their initial values at 80 °C in an ambient environment after 1200 h in the dark. [ABSTRACT FROM AUTHOR]

• The new materials of T-6TPA with high hole mobility of 2.06 × 10−3 cm2V−1s−1 was synthesized for dopant‐free HTL. • The infiltration strategies can further improve the interface hole extraction and transport between HTL and perovskite. • Anti-solvent drip strategy can construct a more effective charge transport channel in the perovskite. • The PCE of PSC with dopant-free T-6TPA HTL has increased from 18.5% to 20.3% with the assistance of antisolvent dripping. • The PSCs with T-6TPA dopant-free HTL presents good long-term stability in both humid air and high temperature of 60 °C. Perovskite solar cells (PSCs) with dopant‐free hole transporting layers (HTLs) deserved extensive research by merits of their outstanding hydrophobicity and stability. However, the low carrier mobility and poor interfacial hole extraction lead to the inferior power conversion efficiency (PCE) than that of conventional Li+ doped Spiro-OMeTAD. Here, a design of triphenylamine groups grafted triphenylene derivative (T-6TPA) as dopant-free HTLs has been presented. The larger π-conjugation in T-6TPA give rise to high hole mobility of 2.06 × 10−3 cm2V−1s−1. Moreover, the interfacial hole extraction of T-6TPA was significantly promoted when the molecules were infiltrated into perovskite before HTL deposition. The infiltration method of anti-solvent dripping (An) strategy increased PCE from 18.5% up to 20.3%, which is superior to another additive doping strategy (Ad-strategy, 19.3%). The effectiveness of An-strategy can be attributed to the construction of a coherent and homogeneous hole transport channel. The hydrophobicity and high glass transition temperature of T-6TPA also granted excellent moisture and thermal stabilities that the initial PCE could remain 80% for 60 days in air or 600 h at 60 °C. This work highlights the synergistical optimization by design of highly hole-mobile materials as well as the interfacial network construction for charge transport. [ABSTRACT FROM AUTHOR]

[Display omitted] • Lewis base groups are introduced into HTMs to restrict ion migration of Li+. • Phen-TPA effectively restricts ion migration of Li+ by strong coordination effect. • PSC based on Phen-TPA achieves a PCE of 20.02% with negligible hysteresis effect. • PSC based on Phen-TPA exhibits preferable humid and thermal stability. • The performance of PSCs is promoted with enhanced coordination ability of HTMs. Li-TFSI as an indispensable dopant for hole transporting materials (HTMs) suffers from inherent hydrophilicity and ion migration, which seriously damages the stability of perovskite solar cells (PSCs). Herein, a facile design strategy is proposed to restrict ion migration of Li+ by introducing different Lewis base groups (pyridine, 1,10-phenanthroline and pyrazine) into HTMs. Owing to the coordination effect of Lewis base groups to Li+, the doped HTMs (Pyrd-TPA, Phen-TPA and Pyra-TPA) exhibit significantly enhanced conjugation and hole mobility. Particularly, theoretical calculation and Fourier-transform infrared spectroscopy (FTIR) results demonstrate that Phen-TPA forms the strongest coordination with Li+ due to the most negative electrostatic potential region existing around 1,10-phenanthroline group. The generated Li+-coordinated Phen-TPA contributes to preferable energy levels, morphology uniformity and hydrophobicity. Element mapping analysis shows that Li-ion migration in doped Phen-TPA is restricted effectively. In addition, Phen-TPA can also passivate the perovskite surface defects dramatically, which facilitates more efficient charge transfer to hole transporting layer. Consequently, PSCs based on Phen-TPA achieve promising power conversion efficiency (PCE) of 20.02% with negligible hysteresis effect. More importantly, it maintains over 88% of the initial PCE after 1056 h storage in ambient condition of 40–60% RH and about 81% of the original efficiency after 264 h storage at 60–70 °C. This work systematically revealed the relation between coordination ability of HTMs and the performance of PSCs for the first time, which provides new design strategies to develop efficient and stable PSCs. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new strategy of developing high-performance dopant-free HTMs for PSCs is presented. • Two novel HTMs with intramolecular π-π interactions were developed for PSCs. • Crystal structures offer information on molecular configuration and interactions. • PSCs based on BFM-C6 showed a PCE of 19.06% with enhanced long-term stability. The development of hole-transporting materials (HTMs), especially dopant-free ones, is of great significance for simultaneously improving the efficiency and stability of perovskite solar cells (PSCs). Herein, two molecularly engineered HTMs (BFM-C1 and BFM-C6) featuring intramolecular π-π interactions are designed based on the well-known spiro-OMeTAD and synthesized via simple synthetic routes. Unlike the spiro-OMeTAD with orthogonal conformation, both BFM-C1 and BFM-C6 are revealed to adopt a "face-to-face" stacking orientation with evident intramolecular π-π interactions, and display about five times higher hole mobilities (≈ 10-4 cm2V-1s−1) than pristine spiro-OMeTAD. Moreover, both the HTMs exhibit high hole extraction capacity likely owing to good electronic contact with the perovskite. Notably, the incorporated long alkyl chains endow BFM-C6 with better film morphology and superior hydrophobicity, as compared with BFM-C1 , thereby resulting in enhanced charge extraction at the perovskite/HTM interface as well as the moisture stability of the perovskite underneath. Consequently, the PSCs employing BFM-C6 as HTM without dopants achieve a power conversion efficiency of 19.06%, along with preferable durability. Furthermore, BFM-C6 -based PSCs also exhibit improved thermal stability as compared to the devices based on doped spiro-OMeTAD. This work not only enriches the variety of dopant-free HTMs for PSCs, but also provide a new strategy for developing high-performance dopant-free HTMs. [ABSTRACT FROM AUTHOR]

We report two simple triphenylamine-based hole-transporting materials (HTMs) containing vinyl derivatives, 3,6-di(2-(4-(N,N-di(p-tolyl)amino)phenyl)vinyl)-2-thiophene (apv-T) and 3,6-di(2-(4-(N,N-di(p-tolyl)amino)phenyl)vinyl)-9-ethyl-carbazole (apv-EC) for the perovskite solar cells. According to theoretical calculation and experimental results, their HOMO energy levels are similar to that of conventional spiro -OMeTAD, which is supposed to be favorable for the hole transportation in the device. Up to 12% of light-to-electricity conversion efficiency has been achieved for the mesoporous TiO 2 /CH 3 NH 3 PbI 3 /apv-EC/Au solar cell without using p -type dopants. Time-resolved photoluminescence (PL) measurement and Electrochemical Impedance Spectra (EIS) further reveal that relatively high hole mobility of the apv-EC and weak recombination occurred at TiO 2 /CH 3 NH 3 PbI 3 /apv-EC interfaces of the device are crucial to the good performance in comparison with the apv-T. Advantages such as easy synthesis, low cost and relatively good cell performance provide a potential application as the replacement of the expensive spiro -OMeTAD. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two novel spiro-type HTMs with a low symmetry feature were developed for PSCs. • The SFHc-S-based PSC achieved a high PCE of 21.52% with improved stability. • Thiocarbonyl groups could efficiently passivate the perovskite surface defects. • Two facilely synthesized spiro cores are reported for designing functional materials. Hole-transporting materials (HTMs) play crucial roles in protecting the perovskite layer, promoting charge extraction, as well as controlling the cost of Perovskite solar cells (PSCs). In order to reduce PSCs cost and simplify PSCs preparation process, more and more attention has been paid to develop multifunctional HTMs. In this work, two novel spiro-fluorene/heterocycle cored bifunctional HTMs, denoted as SFHc-O and SFHc-S respectively, are designed and facilely synthesized. The two HTMs have similar molecular structures, energy levels and thermal properties, but show quite different PSCs performance. Significantly, the heteroatoms in freshly developed spiro cores are demonstrated to have large contributions to device performance. In particular, the sulfur atoms in SFHc-S display a positive impact on both the hole extraction/transport and the defect passivation, which ultimately endow corresponding device with much better performance. The PSC based on SFHc-S obtains a high efficiency excess 21.5% with negligible hysteresis. Moreover, the device with SFHc-S displays enhanced stability, compared to the reference device incorporating spiro-OMeTAD. This work paves a way to develop multifunctional spiro-HTMs for highly efficient and stable PSCs. [ABSTRACT FROM AUTHOR]

The high cost of Spiro-OMeTAD and the poor stability of devices remain a critical challenge for commercialization of perovskite solar cells (PSCs). Hence, the development of efficient hole-transporting materials (HTMs) seems imperative. Herein, three alkyls-modified HTMs named BTPA-C, BTPA-3C and BTPA-8C were designed and synthesized. Through tailoring their alkyl side-chain length, the structure-property relationships such as photophysical, electrochemical properties and the photovoltaic performance of corresponding PSCs were systematically investigated. Results demonstrate that the HTMs exhibit similar energy level, absorption and emission spectra. However, through tailoring their alkyl side-chain length, the film-forming and hole-transporting ability of HTMs can be greatly affected. Compared to BTPA-C or BTPA-8C, BTPA-3C with a moderate side chain length was endowed with the highest PCE of 18.60%, which was even comparable to that of PSCs based on Spiro-OMeTAD. Meanwhile, compared to the latter, PSCs based on BTPA-3C exhibited significantly improved stability at a relative humidity of 45 ± 5%, maintaining more than 80% of the initial efficiency after aging for 30 days. • Three new hole-transporting materials based on benzodithiophene were synthesized, characterized and investigated. • Various length of side-chains were introduced into materials to optimize the film-forming and carrier-transferring ability. • The hydrophobicity of hole-transporting materials partly determined humidity stability of perovskite solar cells. [ABSTRACT FROM AUTHOR]

Hollow TiO 2 spheres were synthesized by template method, with the diameters was 200 nm and the thickness of shell about 30 nm. The high-quality perovskite films fabricated on the hollow TiO 2 mesoporous layer demonstrate smooth surface and large grain size, resulting in the better scattering light ability and fewer defects. The efficiency of the perovskite solar cells prepared on hollow mesoporous layer can reach 17.60%, which is an approximately 14% higher than the PCE of conventional mesoporous layer devices under the same condition. Importantly, the solar cells with hollow TiO 2 can exhibit better stability than the cells with mesoporous TiO 2 after aging 30 days in 65% relative humidity under dark conditions. The results indicate that the hollow TiO 2 mesoporous layer will be a candidate for better efficient and stable CH 3 NH 3 PbI 3 perovskite solar cells, and this structure provides a direction for the design of novel mesoporous layers for perovskite solar cells in future. [Display omitted] • Hollow TiO 2 synthesized by template method shows diameters about 200 nm, along with shell thickness about 30 nm. • The perovskite films fabricated on the hollow TiO 2 demonstrate good morphology and crystallinity, resulting in better scattering light ability and fewer defects. • PCE of cells based on hollow TiO 2 can reach 17.60%, which is 14% higher than that based on conventional TiO 2. • The PSCs based on hollow TiO 2 demonstrate better stability under ambient atmosphere with a relative humidity of 65 ± 5% for 30 days. [ABSTRACT FROM AUTHOR]

• Two ketal derivatives of 9,10-dihydrophenanthrene (DHP) were developed as HTMs for PSCs. • The K-DHP-1 based PSCs delivered a high PCE of 20.52% with negligible hysteresis. • Improved stability was achieved in K-DHP-1 (versus spiro-OMeTAD) based PSCs. • DHP was first revealed as an effective building block for further development of HTMs. It is a very important task of searching for novel hole-transporting materials (HTMs), along with effective building blocks, on the way towards commercialization of the perovskite solar cells (PSCs). 9,10-Dihydrophenanthrene (DHP) is a rigid conjugated system, whose skeleton is closely analogous to the widely used fluorene unit in developing HTMs. Herein, for the first time, DHP employed as a promising building block in the construction of HTMs for PSCs is presented. Two readily-available DHP-cored small molecules, namely K-DHP-1 and K-DHP-2, were synthesized and characterized. An attractive bridged ketal pattern of the two molecules was revealed by the X-ray crystallography of K-DHP-2. Afterwards, the two compounds were applied as HTMs in conventional PSCs with a FA 0.9 MA 0.1 Pb(I 0.9 Br 0.1) 3 • 0.05 CsI perovskite, respectively. Thereinto, the champion device based on doped K-DHP-1 exhibits a power conversion efficiency (PCE) of up to 20.52% with J sc of 23.96 mA/cm2, V oc of 1.09 V and FF of 78.6%, rivalling the performance of device fabricated with spiro-OMeTAD (20.97%). More encouragingly, the K-DHP-1-based PSC displays good long-term stability, remaining 88% of its original performance after storing in atmosphere (30%~50% relative humidity) for 45 d without encapsulation, which is better than the spiro-OMeTAD-based PSC. These results indicate that K-DHP-1 can be an effective HTM to realize high efficiency and stable PSCs, and furthermore DHP can serve as an excellent building block for the development of new HTMs in the future. [ABSTRACT FROM AUTHOR]