Additive engineering by dicyandiamide for high-performance carbon-based inorganic perovskite solar cells

Hole transport layer (HTL)-free all-inorganic CsPbIxBr3-x carbon-based perovskite solar cells (C-PSCs) have attracted much attention due to its low cost and excellent stability. The poor device efficiency is a barrier to constrain its commercialization, mainly due to the large amount of interfacial and bulk defects existed in inorganic perovskite films. In this study, an organic small molecule dicyandiamide (DCD) is added into perovskite precursor as an additive to adjust the crystallization kinetics and passivate defects of inorganic perovskite films, simultaneously. It is demonstrated that the introduction of DCD can not only accelerate the transition process from intermediate phase DMAPbI3 to inorganic perovskite, but also passivate defects through Lewis acid-base interaction between cyano (C≡N), imine (C=N) groups and uncoordinated Pb2+. Meanwhile, the energy level alignment was optimized, which effectively improves the charge transport efficiency of CsPbIxBr3-x C-PSCs. As a result, optimized device shows an enhanced efficiency from 14.07% to 15.84%, accompanied by the improved long-term stability.