Synergetic surface defect passivation towards efficient and stable inorganic perovskite solar cells

Metal halide inorganic perovskites with excellent thermal stability are holding promise for practical application of perovskite solar cells (PSCs). However, ionic defects, especially iodine vacancies or undercoordinated lead, from the perovskite film surface restrain the obtainment of maximum open circuit voltage as well as long term stability of devices. In this regard, reducing the detrimental defects is of priority to further enhance the performance of inorganic PSCs. Herein, we employed an organic amine compound, specifically diethyldithiocarbamic acid diethylamine (DADA), to passivate the ionic defects on the surface of CsPbIxBr3-x inorganic perovskite film. It is found that the electron-rich sulfur atoms from DADA molecule react with undercoordinated Pb in perovskite, while diethylamine cation effectively forms hydrogen bond with halide ion, further strengthening the passivation effect. Such synergetic passivation, together with the improved film morphology, significantly reduces the defect density and prolongs the lifetime of charge carriers within the perovskite film. Moreover, DADA treatment induces an upward shift of the energy band edge of the perovskite layer, which may facilitate hole extraction at the interface. These combination raises the solar cell efficiency from 18.56% to 20.06% under 100 mW cm−2 illumination. More importantly, the mitigation of ionic defects via DADA passivation dramatically improve the devices ambient stability by retaining the PCE of nearly 90% over 800 h in a 30–40% relative humidity environment.