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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] • Completely cross-linked film is obtained on the basis of photoinitiator markedly lowering the cross-linking temperature. • Hole mobility is enhanced by adding photoinitiator. • Energy levels become more suitable through doping photoinitiator. • Cross-linked hole transport layer improves power conversion efficiency of perovskite solar cells. To the best of our knowledge, poor environment stability is the main challenge for perovskite solar cells (PSCs). In this study, cross-linked hole transport layer (HTL) is built on perovskite crystal to guarantee the operation stability of mesoporous PSCs for the first time. Here, N,N' -di-p-tolyl- N,-N' -bis(4-vinylphenyl)-[1,1′-biphenyl]-4,4′-diamine (V-p-TPD) was applied as a hole-transportable polymerizable monomer with the assistance of ultraviolet photoinitiator 4-octyloxydiphenyliodonium hexafluoroantimonate (OPPI). Cross-linking process is conducted at a distinctly low temperature of only 100 °C by adjusting the V-p-TPD: OPPI ratio to 10:1, which is tolerable for the active black phase of perovskite. The resultant cross-linked V-p-TPD film is qualified with a high cross-linking degree of 99%, a high hole mobility of 3.84 × 10−4 cm2V−1s−1 and a hydrophobic surface with wetting angle of 94.6°. Mesoporous PSCs based on the obtained cross-linked HTL achieved a tremendous Power conversion efficiency (PCE) of 18.49%, which represents the state-of-the-art records of mesoporous PSCs with cross-linkable HTL. PCE of the unpackaged device can remain 88% of the initial value after 30 d in an atmospheric environment with a relative humidity of 60 ± 5%, and maintain 86% of the initial PCE after 200 h in 65 ± 2 °C argon atmosphere. This work presents a low-temperature processing strategy for the preparation of cross-linked HTL layer, which does favor to the stable and efficient energy harvesting application. [ABSTRACT FROM AUTHOR]

• HA+ is incorporated into FAPbI 3 -based perovskite to obtain stable α -FAPbI 3. • 1D-HA-phase exists like a "rivet" passivating among the boundary of perovskite. • 1D/3D hybrid dimension structure enhances the stability of FAPbI 3 -based PSCs. • PSC based (FAMACs) 0.85 HA 0.15 achieves a PCE of 21.20%. FAPbI 3 has been greatly developed in Perovskite solar cells (PSCs) profiting from their narrow bandgap, high panchromatic absorption and long carrier diffusion length. Unfortunately, the phase instability of FAPbI 3 -based perovskite restricts its further development in PSCs. Here, hydrazinium cation (HA+: NH 2 NH 3 +) is incorporated into FAPbI 3 -based perovskite to obtain novel 1D/3D hybrid dimension structure with stable α -FAPbI 3 for the first time. The strong hydrogen bonding of HA+ increases the crystallinity and grain size of perovskite. Furthermore, SEM and TEM reveal that the new HA based 1D-phase (1D-HA-phase) exists like "rivet" passivating among the grain boundary of 3D perovskite, forming 1D/3D hybrid dimension structure contributing to the stability of FAPbI 3 -based perovskite. Confocal fluorescence microscopy, time-resolved photoluminescence spectroscopy and Kelvin probe force microscope measurements reveal that the trap state can be effectively restrained and the non-radiative recombination is largely suppressed in HA+ mixed FAPbI 3 -based perovskite film with 1D-HA-phase. Finally, stable α -FAPbI 3 -based perovskite and its film with high crystallinity, smooth surface morphology, excellent photovoltaic performance and few defects are obtained. PSC using (FAMACs) 0.85 HA 0.15 perovskite achieves a power conversion efficiency of 21.20% which can retain 90% at room temperature in ambient environment for 2520 h. [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]

• A green anti-solvent EA method for MA-free quasi-2D DJ phase perovskite films with was reported. • The films presented a more homogeneous phase distribution with reduced defect density, higher mobility and conductivity. • A PCE of 18.86% was obtained, which is the highest for MA-free DJ phase 2D perovskite-based devices. • The devices maintained impressive stabilities under damp heat and continuous illumination at MPP tracking, respectively. The phase distribution of two-dimensional (2D) perovskites is critical for solar cell power conversion efficiency (PCE). Here, we report a simple green anti-solvent (ethyl acetate, EA) method for obtaining uniform phase dispersion of methylamine (MA)-free quasi-2D Dion-Jacobson (DJ) phase perovskite films (DMePDA)FA 3 Pb 4 I 13 (n = 4). The films present a more homogeneous phase distribution for their rapid extraction of solvents and the interaction between Pb2+ and the carbonyl group in EA, resulting in a more shining surface, reduced surface-defect density, higher out-plane mobility, and higher conductivity. We obtain a PCE of 18.86 %, which is the highest for MA-free DJ phase 2D perovskite-based devices. In addition, the target devices maintain 85 % and 90 % of their initial values after 1008 h under 85 % relative humidity at 85 ℃ (ISOS-D-3) and continuous illumination at maximum power point (MPP) tracking at ∼ 45 ℃ (ISOS-L-1), respectively. [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]

• DMF and DMSO induced the termination of perovskite crystals from Pb-X to A-X. • Perovskite crystals with A-X termination have shallower VBM and CBM. • DMSO and DMF induce the regrowth of perovskite crystals with reduced defects. The optimal alignment of semiconductor's electronic energy level with respect to hole-transporting materials (HTMs and ETMs) determines the photovoltaic conversion efficiency of perovskite solar cells (PSCs). The energy level of perovskite can be greatly affected by the crystal surface termination state formed in the perovskite polycrystalline film preparation process. Perovskite featured with Pb-X termination always bears deep energy level which cannot match well HTM. Herein, to regulate the surface termination state of the perovskite crystals, a controlled solvent atmosphere dimethyl sulfoxide (DMSO) and N,N-dimethylformamide (DMF) was employed to induce the regrowth of perovskite crystals. Results prove that the mixed solvent of DMSO and DMF can induce perovskite crystals from Pb-X termination to A-X termination. Density functional theory (DFT) calculations show that the terminated conversion moves the valence and conduction band edge (VBE and CBE) of perovskite crystal to a shallower energy level, which does great favor to match the energy level of HTM, and then contributes to extracting charges. In addition, the defect density of the optimized perovskite polycrystalline film decreased from 1.258 × 1016 to 1.022 × 1016 cm -3, and the depletion width of PSCs increased from 48.9 to 56.1 nm. Profiting from the effective charge extraction and reduced non-radiative recombination, the open circuit voltage of the PSC increased from 0.99 to 1.09 V, and the conversion efficiency boosted from 17.8% to 20.3%.. [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]

• Two pyrene-based hole transport materials are synthesized. • The dopant-free PYR16 using in PSC achieves a higher PCE of 17% than PYR27. • PSC based on dopant-free PYR16 obtains excellent stability at 80 ℃ and under continuous simulated AM 1.5G sunlight soaking. In this work, arylamine branches N 4-[4-[Bis(4-methoxyphenyl)-amino]phenyl]- N 1, N 1-bis(4-methoxyphenyl)-1,4-benzenediamine are introduced to the 1,6- and 2,7-positions of pyrene core to afford two novel HTMs coded PYR16 and PYR27. The influence of different positions of arylamine units on the optical and electronic properties and the performance of PSCs are investigated. The perovskite solar cells (PSCs) using dopant-free PYR16 exhibite a PCE of 17.00%, which is higher than that of PYR27 (14.67%). Furthermore, the PSCs based on PYR16 obtain better stability than those using PYR27 by maintaining 98% of the initial values after 1080 h at 80 ℃ in an ambient environment in the dark and 85% of initial values after 672 h under continuous sunlight soaking in an ambient environment at 45–50 ℃. [ABSTRACT FROM AUTHOR]