Boosting the efficiency and stability of perovskite solar cells through facile molecular engineering approaches

Not only the poor interaction but also trap states at interfaces and grain boundaries are suspected to be responsible for carrier losses in perovskite solar cell (PSC) architecture, leading to inferior photovoltaic performance and long-term stability. Here, facile and effective molecular engineering approaches have been reported by employing a CsF-doped SnO2 electron-transporting layer (ETL) and inserting zwitterion molecules as building blocks between perovskite and hole-transporting layer (HTL). The modification of SnO2 by alkali metal fluoride significantly improved the opto-electronic properties, indicating rapid extraction of photogenerated electrons and better light-harvesting. On the other hand, zwitterion interlayer demonstrated a considerable passivation in multiple defect states at grain boundaries of perovskite film. This strategy yielded an open-circuit voltage (VOC) of 1.23 V for triple-cation perovskite composition with the loss in potential of only 0.37 V. As a result, a considerable efficiency of 21.7% was achieved with negligible hysteresis. More importantly, such engineering approaches exhibited an admissible long-term stability under continuous light soaking at the maximum power point (MPP) tracking by retaining 90% of initial efficiency after ~800 h. In short, these initiatives have simultaneously improved the photovoltaic performance and long-term stability of PSCs. This work severely highlights the utility of molecular engineering approaches in perovskite devices and provides the basis for facilitating industrial applications in the near future.