Synergistic effects of thiocyanate additive and cesium cations on improving the performance and initial illumination stability of efficient perovskite solar cells

Mixed triple-cation (cesium (Cs), methylammonium (MA) and formamidinium (FA)) lead tri-iodide perovskite solar cells (PVSCs) exhibit improved optical and thermal stabilities compared to similar PVSCs without Cs. However, the triple-cation PVSCs still suffer from initial instability under illumination. Here, we report on the improvement of device performance and operational illumination stability of PVSCs via simultaneous incorporation of lead thiocyanate (Pb(SCN)2) additive and Cs cations, which enhances the perovskite crystallinity and lowers the trap density. We systematically investigate the impact of Cs on the device performance of PVSCs and demonstrate stable power conversion efficiencies of up to 20%. Importantly, our PVSCs with Cs and SCN additives sustain maximum power conversion efficiencies of about 19% without noticeable degradation during continuous operation for 20 000 seconds under 100 mW cm−2 AM 1.5G illumination. The excellent illumination stability of our PVSCs is mainly attributed to the reduced defect density and suppressed photodecomposition of the perovskite due to the incorporation of nonvolatile Cs ions.