Reinforcing the efficiency and stability of perovskite solar cells using a cesium sulfate additive

Rapid charge injection and extraction are two critical characteristics craved in electron transporting layers (ETLs) for highly efficient planar perovskite solar cells (PSCs). In this research work, a buried interface reinforcing tactics is demonstrated for assembling highly efficient and stable PSCs via depositing Cs 2 SO 4 precursor films on SnO 2 ETLs. It is found that the incorporation of Cs 2 SO 4 onto SnO 2 layers can increase the electronic conductivity and also improve the surface coverage and interface flatness via Sn–O–Cs bonding. Additionally, sulfate bridges ( SO 4 2 - ) engrafted on the surface of tin oxide generate a seamless integration of high-quality perovskite absorber on ETL that expedite comprehensive transport kinetics in the device. The perovskite morphology is considerably modulated to produce enlarged grain sizes and improved crystallinity. Eventually, PSCs fabricated from Cs 2 SO 4 -SnO 2 composite electrodes display power conversion efficiencies up to 20.93% with high ambient stability and small hysteresis. Under ambient conditions (25–30 °C, 50–65% relative humidity), the device retains 70% of the initial efficiency after degradation testing for 350 h.