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The development of inorganic hole‐transporting materials (HTMs) is one of the most reliable ways to improve the stability of perovskite solar cells (PSCs). However, the un‐optimal buried interfacial contacts and the defects located at the inorganic HTMs/perovskite interface restricted the device's performance. Herein, a phase‐pure CuScO2 has been synthesized and further employed as mesoporous HTM in inverted PSCs. Surprisingly, a facile pretreatment of the hole‐transport layer by a formamidine salt compensates the I− vacancy of the buried perovskite film, thus regulating the interfacial band energy alignment between the HTM and perovskite. This ion compensation strategy can not only in situ repair the ion loss and improve the built‐in electric field, but also decrease the charge injection barrier and suppress the non‐radiative interfacial recombination. Benefiting from these merits, the resulting methylammonium‐free (MA), Cs/FA‐based PSCs displays a power conversion efficiency (PCE) of 22.42% along with excellent thermal and light stability. Moreover, the pre‐buried treatment strategy can be extended to MA‐containing CsFAMA triple‐cation perovskite film, and a champion inverted device delivers a PCE of 23.11%. This study offers a new avenue to the rational design of HTMs for highly efficient and stable PSCs. [ABSTRACT FROM AUTHOR]

It is imperative to improve the quality of light absorber and reduce the charge‐carrier recombination for efficient perovskite solar cells (PSCs). Herein, a synergistic regulation strategy that combines the tailoring of crystallinity and construction of multilayer cascade charge transport layers (CTLs) for inverted CsPbI2Br solar cells is presented. The film quality of CsPbI2Br is well tuned via F− doping. In addition, gradient energy alignment between perovskite and CTLs, i.e., NiOx/Zn:CuGaO2/perovskite and perovskite/TiO2/PC61BM/ZnO, favors the charge transfer and depresses carrier recombination. Noticeably, the TiO2 interlayer with deep valence band maximum effectively blocks the hole back‐transfer from perovskite to PC61BM. These unique characteristics of the novel structured CsPbI2Br device give a champion power conversion efficiency (PCE) of 15.10% along with good thermal and operational stability. Moreover, the graded CTLs can be expanded to methylammonium‐free hybrid perovskite device (Eg = ≈1.76 eV) by delivering a PCE of 18.12%, showing great promise in tandem solar cells for use as top cell. [ABSTRACT FROM AUTHOR]

Current–voltage hysteresis of perovskite solar cells (PSCs) has raised the concern of accurate performance measurement in practice. Although various theories have been proposed to elucidate this phenomenon, the origin of hysteresis is still an open question. Herein, the use of guanidinium cation (Gu+)‐dopant is demonstrated to tailor the crystal structure of mixed‐cation formamidinium‐cesium lead triiodide (FA0.83Cs0.17PbI3) perovskite, resulting in an improved energy conversion efficiency and tunable current–voltage hysteresis characteristic in planar solar cells. Particularly, when the concentration of Gu‐dopant for the perovskite film increases, the normal hysteresis initially observed in the pristine PSC is first suppressed with 2%‐Gu‐dopant, then changed to inverted hysteresis with a higher Gu‐dopant. The hysteresis tunability behavior is attributed to the interplay of charge/ion accumulation and recombination at interfaces in the PSC. Furthermore, compared to the cell without Gu+‐dopant, the optimal content of 2% Gu+‐dopant also increases the device efficiency by 14%, reaching over 17% under one sun illumination. A new method to control current–voltage hysteresis of planar structured FA0.83Cs0.17PbI3 perovskite solar cells (PSCs) is presented while enhancing device efficiency through tailoring the crystal structure of the perovskite compound with a guanidinium cation (Gu+)‐dopant. New insights into the correlation of the dynamics of device hysteresis with the interfacial charge recombination and accumulation in the PSCs are revealed. [ABSTRACT FROM AUTHOR]