Suppressed Degradation and Enhanced Performance of CsPbI Perovskite Quantum Dot Solar Cells via Engineering of Electron Transport Layers.

CsPbI perovskite quantum dots (CsPbI-PQDs) have recently come into focus as a light-harvesting material that can act as a platform through which to combine the material advantages of both perovskites and QDs. However, the low cubic-phase stability of CsPbI-PQDs in ambient conditions has been recognized as a factor that inhibits device stability. TiO nanoparticles are the most regularly used materials as an electron transport layer (ETL) in CsPbI-PQD photovoltaics; however, we found that TiO can facilitate the cubic-phase degradation of CsPbI-PQDs due to its vigorous photocatalytic activity. To address these issues, we have developed chloride-passivated SnO QDs (Cl@SnO QDs), which have low photocatalytic activity and few surface traps, to suppress the cubic-phase degradation of CsPbI-PQDs. Given these advantages, the CsPbI-PQD solar cells based on Cl@SnO ETLs show significantly improved device operational stability (under conditions of 50% relative humidity and 1-sun illumination), compared to those based on TiO ETLs. In addition, the Cl@SnO-based devices showed improved open circuit voltage and photocurrent density, resulting in enhanced power conversion efficiency (PCE) up to 14.5% compared to that of TiO-based control devices (PCE of 13.8%).