Buried interface modification of condensation reflux-processed SnO2 electron transport layers for CsPbBr3 perovskite solar cells

Low temperature solution-processed SnO 2 is favorable for electron transport layer (ETL) of flexible perovskite solar cells (PSCs) owing to their process compatibility. Here, we propose a route of condensation reflux-processed SnO 2 ETLs for PSCs using SnCl 2 source. However, the low temperature SnCl 2 -derived SnO 2 ETLs are inherently associated with a high defect state density as well as a large amount of H + and Cl - residual on the surface, which will cause open-circuit voltage ( V OC ) loss of the devices. To tackle this issue, aqueous solutions of KOH, CsOH, and KCl have been employed to regulate the buried interfaces. The effects of different cations (K + and Cs + ) and anions (OH - and Cl - ) on the photovoltaic performance of the devices have been comparatively explored. The buried interface with KOH modification showed the best effect, which not only improved the quality and light absorption of CsPbBr 3 perovskite layer but also markedly reduced the defect state density at the interface. The optimal device with an architecture of FTO/SnO 2 /KOH/CsPbBr 3 /carbon exhibited a champion power conversion efficiency (PCE) of 7.80 %, V OC of 1.46 V, short-circuit current density ( J SC ) of 7.50 mA/cm 2 , and fill factor ( FF ) of 0.71, compared with the pristine counterpart with a PCE of 5.86 %, V OC of 1.40 V, J SC of 6.37 mA/cm 2 , and FF of 0.66, respectively. The strategy of low temperature-processed SnO 2 ETLs by KOH interface modification may also provide an avenue for other-typed flexible PSCs manufacture.