Stacking n-type layers: Effective route towards stable, efficient and hysteresis-free planar perovskite solar cells

Perovskite solar cell (PSC) has drawn widespread concern for its high efficiency and facile low-temperature solution fabrication, promising for the alternative low-cost photovoltaic energy. However, before commercializing, the problems regarding to the environmental stability and electrical hysteresis of PSCs still need to be tackled. We present a simple route by stacking n-type materials TiO 2 (spray pyrolysis) and SnO 2 (aqueous colloidal) for planar devices, and achieve a stable (~91% efficiency >90 days at 30%RH without encapsulation), hysteresis-free (hysteresis index 0.004) and efficient (18.03%) perovskite solar cells. Moreover, we carry out a system stability evaluation for unsealed devices under harsh conditions with intense UV illumination, heat and damp in an environmental chamber . Both TiO 2 and SnO 2 devices demonstrate inferior performance compare to the stacked samples in the accelerated stability tests. Photoluminescence , phase and electrical characterizations suggest that the performance enhancement is ascribed to the synergetic optimization from concealing the defective interface and promotion of carriers transfer and blocking. With the optimized n-type layers, a high efficiency of 14.39% is obtained for the 5 × 5   cm 2 sub-module. These results suggest that by stacking n-type layers could enable superior overall performances to common electron transport layers (ETLs) (TiO 2 , SnO 2 and etc.), providing facile routes for fabricating efficient PSCs with high stability.