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Hole‐transporting material (HTMs) are crucial for obtaining the stability and high efficiency of perovskite solar cells (PSCs). However, the current state‐of‐the‐art n‐i‐p PSCs relied on the use of 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxyphenylamine)‐9,9′‐spirobifluorene (spiro‐OMeTAD) exhibit inferior intrinsic and ambient stability due to the p‐dopant and hydrophilic Li‐TFSI additive. In this study, a new spiro‐type HTM with a critical quasi‐planar core (Z‐W‐03) is developed to improve both the thermal and ambient stability of PSCs. The results suggest that the planar carbazole structure effectively passivates the trap states compared to the triphenylamine with a propeller‐like conformation in spiro‐OMeTAD. This passivation effect leads to the shallower trap states when the quasi‐planar HTMs interact with the Pb‐dimer. Consequently, the device using Z‐W‐03 achieves a higher Voc of 1.178 V compared to the spiro‐OMeTAD's 1.155 V, resulting in an enhanced efficiency of 24.02 %. In addition, the double‐column π–π stacking of Z‐W‐03 results in high hole mobility (~10−4 cm2 V−1 s−1) even without p‐dopant. Moreover, when the surface interface is modified, the undoped Z‐W‐03 device can achieve an efficiency of nearly 23 %. Compared to the PSCs using spiro‐OMeTAD, those with Z‐W‐03 exhibit enhanced stability under N2 and ambient conditions. This superior performance is attributed to the quasi‐planar core structure and the presence of multiple CH/π and π–π intermolecular stacking in Z‐W‐03. The multiple CH/π and π–π intermolecular contacts of HTMs can improve the hole hopping transport. Therefore, it is imperative to focus on further molecular structure design and optimization of spiro‐type HTMs incorporating quasi‐planar cores and carbazole moieties for the commercialization of PSCs. [ABSTRACT FROM AUTHOR]

Herein, Cu(II)Pcs and Ni(II)Pcs peripherally tetra‐functionalized with 5‐hexylthiophene (HT), 5‐hexyl‐2,2′‐bithiophene (HBT), and tertbutyl groups (TB) are readily synthesized and employed as hole‐transporting materials (HTMs) in mixed‐ion perovskite ([FAPbI3]0.85[MAPbBr3]0.15) solar cells, achieving power conversion efficiencies (PCEs) up to 20.0%. Remarkably, both the peripheral functionalization and the central metal are found to play a role in the performance. Through a combination of experimental and theoretical techniques, it is found that the simplest HTM, TB‐CuPc, is the best‐performing HTM primarily due to its higher hole mobility and a more appropriate highest‐occupied molecular orbital, whose enables efficient hole extraction without open‐circuit voltage (Voc)losses. This derivative leads to PCEs of 19.96%, which are among the highest values for Pc‐based HTMs. Importantly, devices incorporating these HTMs present significantly higher stability compared to those based on spiro‐OMeTAD. The results here presented pave the way for more realistic, efficient, and inexpensive photovoltaic devices using phthalocyanine derivatives. [ABSTRACT FROM AUTHOR]

With the rapid development in perovskite solar cell (PSC), high efficiency has been achieved, but the long‐term operational stability is still the most important challenges for the commercialization of this emerging photovoltaic technology. So far, bi‐dopants lithium bis(trifluoromethylsulfonyl)‐imide (Li‐TFSI)/4‐tert‐butylpyridine (t‐BP)‐doped hole‐transporting materials (HTM) have led to state‐of‐the art efficiency in PSCs. However, such dopants have several drawbacks in terms of stability, including the complex oxidation process, undesirable ion migration and ultra‐hygroscopic nature. Herein, a fluorine‐containing organic Lewis acid dopant bis(pentafluorophenyl)zinc (Zn‐FP) with hydrophobic property and high migration barrier has been employed as a potential alternative to widely employed bi‐dopants Li‐TFSI/t‐BP for poly[bis(4‐phenyl)(2,4,6‐trimethylphenyl)amine] (PTAA). The resulting Zn‐FP‐based PSCs achieve a maximum PCE of 20.34 % with hysteresis‐free current density‐voltage (J‐V) scans. Specifically, the unencapsulated device exhibits a significantly advanced of operational stability under the International Summit on Organic Photovoltaic Stability protocols (ISOS−L‐1), maintaining over 90 % of the original efficiency after operation for 1000 h under continuous 1‐sun equivalent illumination in N2 atmosphere in both forward and reverse J‐V scan. [ABSTRACT FROM AUTHOR]

Hexakis(hexyloxy)triphenylene (HAT6) discotic liquid crystal is employed as a transparent hole‐transporting material (HTM) for perovskite solar cells (PSCs) and a power conversion efficiency (PCE) of 15.7% is obtained, which is the highest using HAT6 type of HTMs. Despite lower PCE than spiro‐OMeTAD‐based devices (20.3%), the PSCs based on HAT6 exhibit much higher ambient and thermal stability. A fused polyaromatic core with six alkyl chains leads to high hydrophobicity, and the π‐stacked molecular columns of the HAT6 shield the bis(trifluoromethane)sulfonamide lithium salt dopant migration into the perovskite absorber. The PSCs (under N2 condition) exhibit superior stability compared to the devices employing spiro‐OMeTAD, retaining nearly 92% of their initial efficiency after 1200 h operation. Under ambient conditions, HAT6‐based hole‐transportation layer devices retain 93% of the initial efficiency for 690 h. Under continuous thermal stress of 85 °C, the devices based on HAT6 retain 95% of the initial PCE. The results demonstrate the time applicability of liquid crystal for stable PSCs fabrication. [ABSTRACT FROM AUTHOR]

In this study, a series of donor–acceptor–donor (D‐A‐D) type small molecules based on the fluorene and diphenylethenyl enamine units, which are distinguished by different acceptors, as holetransporting materials (HTMs) for perovskite solar cells is presented. The incorporation of the malononitrile acceptor units is found to be beneficial for not only carrier transportation but also defects passivation via Pb–N interactions. The highest power conversion efficiency of over 22% is achieved on cells based on V1359, which is higher than that of spiro‐OMeTAD under identical conditions. This st shows that HTMs prepared via simplified synthetic routes are not only a low‐cost alternative to spiro‐OMeTAD but also outperform in efficiency and stability state‐of‐art materials obtained via expensive cross‐coupling methods. [ABSTRACT FROM AUTHOR]

Hole‐transporting materials (HTMs) based on the 10H, 10′H‐9,9′‐spirobi [acridine] core (BSA50 and BSA51) were synthesized, and their electronic properties were explored. Experimental and theoretical studies show that the presence of rigid 3,6‐dimethoxy‐9H‐carbazole moieties in BSA 50 brings about improved hole mobility and higher work function compared to bis(4‐methoxyphenyl)amine units in BSA51, which increase interfacial hole transportation from perovskite to HTM. As a result, perovskite solar cells (PSCs) based on BSA50 boost power conversion efficiency (PCE) to 22.65 %, and a PSC module using BSA50 HTM exhibits a PCE of 21.35 % (6.5×7 cm) with a Voc of 8.761 V and FF of 79.1 %. The unencapsulated PSCs exhibit superior stability to devices employing spiro‐OMeTAD, retaining nearly 90 % of their initial efficiency after 1000 h operation output. This work demonstrates the high potential of molecularly engineered spirobi[acridine] derivatives as HTMs as replacements for spiro‐OMeTAD. [ABSTRACT FROM AUTHOR]

The under‐coordinated defects within perovskite and its relevant interfaces always attract and trap the free carriers via the electrostatic force, significantly limiting the charge extraction efficiency and the intrinsic stability of perovskite solar cells (PSCs). Herein, self‐diffusion interfacial doping by using ionic potassium L‐aspartate (PL‐A) is first reported to restrain the carrier trap induced recombination via the reconstruction of energy level structure at SnO2/perovskite interface in conventional n‐i‐p structured PSCs. Experiments and theories are consistent with the PL‐A anions that can remain at the SnO2 surface due to strong chemical adsorption. During the spin‐coating of the perovskite film, the cations gradually diffuse into perovskite and endow an n‐doping effect, which provides higher force and a better energy level alignment for the carrier transport. As a result, they obtained 23.74% power conversion efficiency for the PL‐A modified small‐area devices, with dramatically improved open‐circuit voltage of 1.19 V. The corresponding large‐area devices (1.05 cm2) achieved an efficiency of 22.23%. Furthermore, the modified devices exhibited negligible hysteresis and enhanced ambient air stability exceeding 1500 h. [ABSTRACT FROM AUTHOR]

Organic hole‐transporting materials (HTMs) based on the Ullazine core yield so far only moderate power conversion efficiencies of up to 13.08% in perovskite solar cells (PSCs). Aiming to fabricate efficient and stable PSCs, novel Ullazine derivatives bearing thiophene units were designed and synthesized, allowing modulation of the electronic states of the HTMs and further providing defect passivation of the perovskite surface. Experimental and theoretical analysis show that thiophene units with ‐N(p‐MeOC6H4)2 groups improve the conductivity of Ullazine HTMs, boosting the efficiency of PSCs to 20.21%. This value is the highest reported to date for Ullazine‐based HTMs, and is close to the performance of Spiro‐OMeTAD. In addition, unencapsulated PSCs based on the champion Ullazine exhibit superior stability with respect to Spiro‐OMeTAD, retaining nearly 90% of the initial efficiency following 1000 h aging, which is ascribed to a combination of higher water repellency and passivation of defects on the perovskite surface. This work demonstrates the high potential of HTMs based on Ullazine core as substitutes to Spiro‐OMeTAD. [ABSTRACT FROM AUTHOR]

In perovskite solar cells (PSCs), the interfaces of the halide perovskite/electron transport layer (ETL) and ETL/metal oxide electrode (MOE) always attract and trap free carriers via the surface electrostatic force, altering quasi‐Fermi level (EFq) splitting of contact interfaces, and significantly limit the charge extraction efficiency and intrinsic stability of devices. Herein, a graded "bridge" is first reported to link the MOE and perovskite interfaces by self vertical phase separation doping (PSD), diminishing the side effect of notorious ionic defects via both reinforced interface Ebi and the vacancies filling. Experimental and theoretical results prove that the inhomogeneous distribution of CsF in the bulk or surface of PC61BM would not only form metal–oxygen (M–O) dipole on MOE, reinforcing the interface Ebi, but also create a graded energy bridge to alleviate the disadvantage of band offset raised by the enhanced interface Ebi, which significantly avoid the carrier accumulation and recombination at defective interfaces. Employing PSD, the power conversion efficiency of the devices approaches 21% with a high open‐circuit voltage (1.148 V) and delivers a high stability of 89% after aging 60 days in atmosphere without encapsulation, which is the highest efficiency of organic electron transport layers for n–i–p PSCs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hole-transporting material (GW-4) is easily synthesized without metal catalysts. • GW-4 has a much lower synthesis cost and fabrication dosage than spiro-OMeTAD. • PCE of device with doped GW-4 exceeds that of spiro-OMeTAD-based one. • Polycarbonate (PC) polymer is first introduced to modulate the interfaces. • Device fabricated with PC /pristine GW-4 displays an excellent humid stability. Dopant-free hole-transporting materials (HTMs) and interface modification are two effective approaches for developing sustainable perovskite solar cells (PSCs). In this work, dopant-free HTM (GW-4) containing an N -ethyl-carbazole with two rotatable vinyl linkages is first synthesized by a green chemical method without any metal catalysts. The GW-4 cost is only 22.43% of the price of commercial 2,2′,7,7′-tetrakis[ N , N -di(4-methoxyphenyl)amino]-9,9′-spirobifluorene (spiro-OMeTAD). In the device fabrication, the concentrations of doped GW-4 (20 mg mL−1) and pristine GW-4 solutions (10 mg mL−1) are much lower than that of spiro-OMeTAD solution (doped, 72.3 mg mL−1). The power conversion efficiency (PCE) of doped GW-4 -based cell is 20.45%, superior to that of spiro-OMeTAD-based cell (19.59%). As the optimal concentration of dopant-free GW-4 is insufficient to completely cover the perovskite layer, a polycarbonate (PC) polymer with carbonyl groups is first introduced to modulate perovskite grain boundaries and improve film-forming property of pristine GW-4. The cell with PC /pristine GW-4 has a slightly higher PCE (17.92%) than the cell with pristine GW-4 (17.66%). Regarding humid stability, after 455 h, the doped GW-4 and spiro-OMeTAD based PSCs retain only 11.71% and 2.27% of the initial efficiency, respectively. In striking contrast, after 850 h, the pristine GW-4 and PC /pristine GW-4 based devices retain 69.74% and 97.53% of the initial efficiency, respectively. This study provides both a new molecular design strategy to develop highly efficient dopant-free HTMs and an ingenious interfacial contrivance to overcome the defects of incomplete coverage of HTM film on perovskite layer and understand the charge dynamics at interfacial layers. [ABSTRACT FROM AUTHOR]

The major obstacles delaying the commercialization of thin film solar cells based on hybrid organic halide perovskite are the expensive materials, instability of the devices and the complicated multi-step fabrication process. To solve these challenges, we present a simple and high material utilization strategy which employing the polyethyleneimine (PEI) interface abduction to in-situ fabricate perovskite layer and hole transporting layer (HTL) from MAPbI 3 and Spiro-OMeTAD (SPI) mixed precursors in single step. Analyzation find that the in-situ phase separation is induced by the PEI abduction. The existence of PEI blocks SPI form Ti–O bond with bottom TiO 2 surface and converting the interaction between SPI and bottom interface to Van der Waals interaction. Employing this fabrication technique for PSCs, remarkably improves materials utilization of perovskite and SPI, as well as exhibiting superior stability of about 95% initial efficiency even after 68 days of storage in ambient condition without encapsulation. We believe that our strategy will pave a new way for simple, economical and stable PSCs preparation, and provide an inspiration to simplify fabrication process for organic-inorganic electronic devices. Image 1 •Depositing two layers (perovskite and hole transportation layer) by single step. •A phase separated strategy for mixed materials with different polarities. •The process is dozens of times for the cost saving. •The devices employing phase separated strategy exhibit higher air stability. [ABSTRACT FROM AUTHOR]

• Novel tetrathiafulvalene (TTF) derivative has been implemented as a dopant free HTM for PSC. • Higher intrinsic hole mobilities as compared to Spiro-OMeTAD. • Remarkable undoped PCE of 15.66%. • Excellent ambient stability. Performance of hole transporting material (HTM) plays a fundamental role in estimating overall efficiency of perovskite solar cell (PSC). Dopant free HTMs with high intrinsic hole mobility and stability have been emerged as a fascinating choice for production of highly efficient and stable PSCs. Here, we report facile synthesis and implementation of a novel tetrathiafulvalene (TTF) derivative as a dopant free HTM for efficient and ambient stable PSC. The PSC based on dopant free TTF HTM shows remarkable photovoltaic efficiency of 15.66% which is one of highest value for any TTF based HTM. Beside efficiency, PSC based on TTF HTM shows only about 16% decline in initial efficiency even after 45 days storage in ambient conditions without any encapsulation which verifies its excellent ambient stability and hydrophobicity. Furthermore, various physical, electrochemical, photovoltaic and optical parameters of TTF HTM are investigated by highly specialized characterization tools. We affirm these results will be helpful for developing novel HTMs for highly efficient and stable PSCs in future. [ABSTRACT FROM AUTHOR]

Abstract With close to 100% internal quantum efficiency over the visible light region, photocurrents in perovskite solar cells (PSCs) are at their practical limits. Achieving high open-circuit voltage (V oc) and fill factor (FF) are imperative to further improve the power conversion efficiency (PCE) of PSCs. Here, we demonstrate that V oc and FF of PSCs can be significantly improved from 1.03 to 1.09 V and from 0.71 to 0.75, respectively, by modifying TiO 2 with 4- tert -butyl pyridine (t -BP), resulting in 9% improvement in PCE from 16.14% to 17.58% for the best performing devices. To illuminate origin of increased PCE by t -BP modification, UPS, PL and EIS are performed. The results reveal that t -BP modification improves efficiency through two separated mechanisms. First, t -BP interfacial dipole layer can tune Fermi energy level and work function of TiO 2 , thus increasing built-in potential and improving band alignment at TiO 2 /CH 3 NH 3 PbI 3 interface. Second, reduced defect states of TiO 2 by specific binding of t -BP at defect sites, resulting in reduction of charge recombination are found to be another mechanism for increased efficiency. Meanwhile, the lower defect states on TiO 2 further make contribution to reduce hysteresis of PSCs. These results will pave the way for high efficiency and low hysteresis PSCs. Graphical abstract Image 1 Highlights • A highest PCE of 17.58% has been achieved for the PSC with t -BP modified TiO 2. • The t -BP has dual function for TiO 2 : tune energy level and reduced defect states. • PSCs based on t -BP modified TiO 2 show higher efficiency and lower J-V hysteresis. • The mechanisms of PSCs with high efficiency, low hysteresis have been illuminated. [ABSTRACT FROM AUTHOR]

Abstract The electron transporting layer/perovskite interface is crucial to the power conversion efficiency of perovskite solar cell. In this work, we study the effect of bifunctional 4-picolinic acid self-assembled monolayer as electron transporting layer/perovskite interface linker on perovskite crystallinity and electron transporting layer/perovskite interface transfer property for high performance perovskite solar cell. Our result shows that the 4-picolinic acid self-assembled monolayer modified device exhibits the highest efficiency of 18.90% and negligible hysteresis index of 0.03 under illumination of AM 1.5G (100 mW cm−2), compared to that (14.65%) of the unmodified device. It can be concluded that the bifunctional self-assembled monolayer can be grappled with the TiO 2 , increase grain sizes of MAPbI 3 , effectively passivate TiO 2 /perovskite interface, and preferably balance electrons and holes transfer, which significantly improves device performance with negligible hysteresis. Our results also indicate bifunctional self-assembled monolayer is a preferable pathway for fabricating high performance and low hysteresis perovskite solar cells. Graphical abstract Image 1 Highlights • Bifunctional 4-picolinic acid interface linker was studied. • The 4-picolinic acid optimizing device exhibits the highest PCE of 18.90%. • The 4-picolinic acid optimized PSC exhibits negligible hysteresis. • Bifunctional interface linker is a preferable pathway for highly efficient PSCs. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Dual-functional pyridinesulfonic acid self-assembled monolayers were studied. • Effect of functional group position change on device performance was studied. • 3-Pyridinesulfonic acid can easier passivate TiO 2 /perovskite interface. • The optimized device obtains the champion PCE of 16.88%. Abstract There are fewer researches on the effect of functional group position change on device performance for highly efficient perovskite solar cell. In this work, we take pyridinesulfonic acid as an example, and study the effect of the isomeride: 2- and 3-pyridinesulfonic acid self-assembled monolayer on device performance for highly efficient perovskite solar cell. The efficiency of control device is 14.65% (Hysteresis Index = 0.31) under illumination of a simulated sunlight (AM 1.5G, 100 mW cm−2). Through use of the 3-pyridinesulfonic acid self-assembled monolayer, the device exhibits striking improvements to reach the efficiency of 16.88% (Hysteresis Index = 0.02), which constitutes an enhancement compared to those of 2-pyridinesulfonic acid self-assembled monolayer modified device (16.54%, Hysteresis Index = 0.02). The enhanced photovoltaic performances can be attributed to the larger perovskite grain sizes, and easier passivation of electron transporting layer/perovskite interface, which promote the charge separation, transport and collection. [ABSTRACT FROM AUTHOR]

By using the Cs-doped MAPbI 3 as the model perovskite materials, several effects arising from the doping of Cs+ into hybrid perovskites have been summarized. Significantly, a suppression of ion migration effects and an improvement in the diffusion length were observed. The Cs+ doped PSCs showed hysteresis-free behavior, device efficiency boosted from 19.73% to 21.72%, and the fabricated modules (6.5 cm × 7 cm) with a high PCE of 21.08% via "non-destructive replicate" of all photovoltaic parameters from small device. [Display omitted] • Cs-doped MAPbI 3 acts as the model perovskite materials. • Doping of Cs+ into hybrid perovskites significantly suppresses ion migration. • Cs+ doping noticeably increases the carrier diffusion length of the perovskite film. • The Cs+ doped PSCs showed hysteresis-free behavior. • Fabricated cell efficiency reached 21.72%, and module over 21.08% Perovskite solar modules have been attracting increasing attention due to their market potential, yet publications concerned with theintrinsic scale-up potential of different perovskite compositions remain relatively scarce. On the other hand, while great success is being made towards improving the power conversion efficiency (PCE) of perovskite solar cells (PSCs) by cesium cation (Cs+) doping of the perovskite, more attention is being paid to the perovskite phase stabilization effect of Cs+ doping, and less to other properties that are critical to understand and futher improve the PSC's. In this work, moderately-Cs-doped MAPbI 3 was employed as a model perovskite material in order to exclude the phase stabilization effect. Our systematic study revealed the influence of Cs+ in organic–inorganic hybrid perovskites on the crystal structure, crystallization process, trap state density, band structure and charge (i.e. , ions or photo-carriers) transport. Markedly, it has been observed that Cs+ doping can greatly increase the carrier diffusion length in the perovskite films, thus improving the potential to scale-up PSC's.The PCE of small area devices (0.09 cm2) was increased to 21.72% from 19.73%, with decreased hysteresis behavior and increased operational stability (T 85 = 1000 h) after Cs+ doped, where T 85 refers to the retention of 85% of the initial PCE. Moreover, a PCE of 21.08% was obtained for a Cs+-containing perovskite module with an active area > 30 cm2, which demonstrates a better "reproducibility" than the reference sample (MAPbI 3 -based perovskite modules, PCE = 18.26%). [ABSTRACT FROM AUTHOR]

Generally, TiO 2 -based perovskite solar cell (PSC) is beneficial to high efficiency but poor ultraviolet (UV) light stability. Here, we report that a highly efficient Mg x Zn 1-x O-based (MZO-based) PSC with excellent UV light stability. MZO has a higher electron mobility and deeper conduction band than traditional TiO 2 , which can reduce the charge accumulation at the MZO/perovskite interface and enhance the charge transfer from perovskite to MZO. Furthermore, the reduced interface loss and energy barrier are beneficial to obtain high open-circuit voltage (V oc). By optimizing, the MZO-based device shows a high V oc of 1.11 V, yielding a promising efficiency of 19.57%. The MZO-based device (unencapsulated) retains 76% of its initial short-circuit current density (J sc) after 1 year air aging (room temperature, relative humidity: 40–80%) and 8 h UV irradiation (365 nm, 35 W), versus only 12% under the same condition for TiO 2 -based device. The good UV light stability of MZO-based device can be attributed to the reduced electron trap-state density in MZO electron-transporting layer (ETL). Specifically, zinc interstitial and oxygen vacancy mediated defect sites of MZO ETL are effectively passivated, which tightly protects the perovskite layer from degradation under UV light. Our results show a great potential for MZO ETL application in UV-stable PSC. Image 1 • A wet-chemical route for low-temperature Mg x Zn 1-x O nanocrystals is reported. • The champion PCE of Mg x Zn 1-x O-based perovskite solar cell is 19.57%. • The V oc is 1.11 V, keeping up with that (1.11 V) of SnO 2 -based n-i-p device. • Device retains 76% of initial J sc after 1 year air aging and 8 h UV irradiation. [ABSTRACT FROM AUTHOR]