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• 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]