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harmful phase separation behavior, which makes it the most prominent candidate for high-efficiency single-junction cells or sub-cell absorbers in tandem cells. [1,2] It has witnessed tremendous progress in inorganic CsPbI 3 -based perovskite solar cells (PSCs) under unremitting efforts over the past few years, especially on stabilizing photo-active black phase and improving perovskite crystal quality. [3][4][5] However, the power conversion efficiency (PCE) of CsPbI 3 -based PSCs still remains inferior to that of organic-inorganic hybrid PSCs, primarily due to the serious photovoltage loss triggered by nonradiative charge carrier recombination. [5][6][7] Suffering from severe photovoltage loss, the open-circuit voltage (V OC ) reaches only 80% of the Shockley-Queisser (S-Q) theoretical limit, critically impeding further advancements in performance. [8][9][10] In this regard, reducing the V OC deficit is of great significance for promoting the efficiency of CsPbI 3 -based photovoltaics.Several approaches including additivesassisted crystallization techniques, post-treatment strategies, and antisolvent engineering methods have been developed to suppress the V OC deficit in CsPbI 3 -based solar cells. [11] Thereinto, additives engineering such as introducing inorganic ammonium halides, alien elements, and molten salts into the precursor solution has been proven to be an effective means through manipulating crystallization growth and enhancing perovskite crystallinity. [1,3,12] Alternatively, post-treatment on perovskite surfaces with 2D materials or methylammonium chloride has seen aroused interest to demonstrate some advantages in reducing V OC loss. [8,13] Moreover, employing solvent molecular sieves in the antisolvent induced rapid nucleation and slow crystal growth of CsPbI 3 films, thereby diminishing energy loss in photovoltaic devices. [5] Nevertheless, most strategies concentrated on the bulk or the top surfaces of CsPbI 3 perovskite. Little attention has been paid to tackling the bottleneck issues of the buried interface under CsPbI 3 perovskite thin films, resulting in a huge room to restrain the V OC deficit.Generally, the perovskite layer is clamped by the atop hole electron layer (HTL) and the bottom titanium oxide (TiO 2 ) electron transport layer (ETL) in a typical regular CsPbI 3 -based PSCs structure. The buried interface between TiO 2 ETL and perovskite possesses higher concentrations of imperfections than that of Although CsPbI 3 perovskites have shown tremendous potential in the photovoltaic field owing to their excellent thermal stability, the device performance is seriously restricted by severe photovoltage loss. The buried titanium oxide/perovskite interface plays a critical role in interfacial charge transport and perovskite crystallization, which is closely related to open-circuit voltage deficit stemming from nonradiative recombination. Herein, target molecules named 3-sulphonatopropyl acrylate potassium salts are deliberately employed with special functional groups for modifying the buried...

Growth mechanism and temperature of monoclinic gallium oxide (β‐Ga2O3) films grown by ozone molecular beam epitaxy (MBE) are investigated herein. Phase‐pure (2true¯01) β‐Ga2O3 films can be grown on c‐plane sapphire substrates when the growth temperature exceeds 500 °C, and the grain size increases with the increase in the growth temperature. Sixfold rotational domains are obtained based on the epitaxial relationships (Ga2O3 < 010>//Al2O3<11true¯00> and Ga2O3 < 102>//Al2O3 < 11true2¯0>). For the film grown at 700 °C, the threefold facets are observed for the first time, which are resulted from the easy‐cleaved (100) plane and rotational domains. In addition, the cathodoluminescence spectra of the β‐Ga2O3 films show that the proportion of ultraviolet emission increases with the increase in the growth temperature, which is attributed to the modulation of defect. Finally, the growth rate can be modulated by the ratio of Ga flux and ozone pressure. A reference is provided for heteroepitaxy of β‐Ga2O3 films and better understanding of the ozone MBE growth mechanism of oxides.

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