Atomic Layer Deposited Tin Oxide Buffer Layer via Layer‐by‐layer Growth for Efficient Semitransparent Perovskite Solar Cells

Abstract Atomic layer deposition (ALD) of compact tin oxide (SnO 2 ) sputtering buffer layer plays a crucial role in high‐performance semitransparent perovskite solar cells (ST‐PSCs) and perovskite/silicon tandem solar cells. However, when the substrate exhibits low reactivity with the ALD reactants, the ALD process tends to follow an island growth mode, leading to a prolonged incubation period and pinhole films, which ultimately degrade device performance. In this study, the substrate is activated by simply altering precursor introduced sequence, switching from introducing the tin precursor first to introducing the oxygen precursor first. The hydroxyl groups generated by the oxygen precursor enhance nucleation sites on the substrate, allowing the initial ALD films growth transforming from island‐like mode to layer‐by‐layer mode, resulting in dense and vertically uniform SnO 2 films. Semitransparent PSCs constructed with dense ALD SnO 2 layer effectively mitigate sputtering‐induced damage and improve the interface properties. As a result, the initial power conversion efficiency (PCE) of the ST‐PSC increased from 19.37% to 19.99%, corresponding to the improvement by 3.2%. The perovskite/silicon tandem solar cells are also fabricated with PCE of 28.77%. Furthermore, ST‐PSCs with dense ALD SnO 2 layer exhibit improved moisture and thermal stability, which maintain 96.6% and 95.6% of initial PCE after being stored at relative humidity of 30% for 600 h and 85 °C for 600 h, respectively. This study provides a simple and effective approach for fabricating dense and uniform ALD SnO 2 buffer layers, demonstrating their potential application not only in efficient semitransparent perovskite solar cells and tandem solar cells but also in other optoelectrical devices.