Defect Passivation of Low-Temperature Processed ZnO Electron Transport Layer with Polyethylenimine for PbS Quantum Dot Photovoltaics

Lead sulfide (PbS) colloidal quantum dot solar cells (CQDSCs) present the distinctive ability to utilize short-wave infrared light, good ambient stability, and convenient solution-based fabrication processes and thus attract much attention in the photovoltaic research field. The performance of CQDSCs has been improved by constructing the ZnO/PbS heterojunction, due to suitable band levels and electron mobility of ZnO electron transfer layer (ETL). However, the huge number of defects in low-temperature processed ZnO cause an unbalanced carrier-related processes, which restrict further performance enhancement and flexible production of CQDSCs. Here, we described a facile method to passivate defects in low-temperature sol–gel ZnO by introducing polyethylenimine (PEI) into the precursor solution. Versus the original ZnO film, the composite ZnO:PEI films exhibit better crystallization because of the Zn–N interaction. A series of electronic analyses have shown that the addition of PEI reduces the work function ...