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

Hole transport layer (HTL)-free, all-inorganic CsPbI_xBr_3-x carbon-based perovskite solar cells (C-PSCs) have attracted much attention due to their 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 to the 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 the Lewis acid-base interaction between cyano (C[tbnd]N), imine (C[dbnd]N) groups, and uncoordinated Pb²⁺. Meanwhile, the energy level alignment was optimized, which effectively improves the charge transport efficiency of CsPbI_xBr_3-x C-PSCs. As a result, optimized device shows an enhanced efficiency from 14.07% to 15.84%, accompanied by improved long-term stability.