Tail states suppression via surface-modification of wide-bandgap perovskites for high-efficiency all-perovskite photovoltaic tandems.

• Time-resolved microwave conductivity (TRMC) was employed to assess charge carrier mobilities and recombination rate constants in perovskite films. The findings reveal that the post-treatment strategy enhances film quality, improves carrier mobility, and reduces non-radiative recombination. • We fabricate inverted WBG PSCs with a structure of ITO/MeO-2PACz/perovskite/C60/ALD-SnO 2 /Cu. These PSCs yields a champion PCE of 21.48% with negligible hysteresis. • A perovskite/perovskite four-terminal tandem solar cell with efficiency of 28.07% is achieved. This is one of the highest efficiencies reported for all-perovskite tandem solar cells. As an essential light-absorbing material in perovskite-based tandem solar cells, wide-bandgap (WBG) perovskite has garnered extensive attention. Nevertheless, due to severe non-radiative recombination from tail states, as well as photoinduced phase segregation and unoptimized charge transfer, WBG perovskite solar cells (PSCs) typically display significant open-circuit voltage (V OC) loss and low fill factor (FF). In this work, we report to modify the 1.68 eV WBG perovskite film upon optimized surface passivation with 1,3-propane-diammonium iodide (PDAI 2). Time-resolved microwave conductivity measurement is employed to analyze the tail states, mobilities of charge carriers and the rate constants of recombination in perovskite films. The results indicate that the optimized surface modification strategy not only enhances film quality, boosts carrier transport, but also suppresses tail states and therefore diminishes non-radiative recombination, consequently elevating the V OC and FF of the device. Hence, the PDAI 2 -assisted WBG PSCs deliver an optimal efficiency of 21.48 %, accompanied by a V OC of 1.243 V. Furthermore, the integration of a narrow-bandgap tin–lead PSC with a semi-transparent WBG PSC results in a four-terminal perovskite/perovskite tandem solar cell, showcasing an efficiency surpassing 28 %. Our research offers a practical approach for producing efficient WBG PSCs and tandem solar cells. [ABSTRACT FROM AUTHOR]