PbS Quantum Dot Solar Cells Integrated with Sol–Gel-Derived ZnO as an n-Type Charge-Selective Layer

Abstract

ZnO thin films fabricated by a low-temperature sol–gel conversion method (L-ZnO) were employed as n-type electron-transporting layers (ETLs) in depleted-heterojunction quantum dot solar cells (DH-QDSCs). Thin films of PbS (∼200 nm) fabricated by spin-coating a colloidal PbS QD solution layer by layer were used as the p-type photoactive layers. The L-ZnO films functioned as efficient n-type ETLs by fully completely depleting the PbS active layers, and they displayed performances much higher than those of conventional ZnO nanoparticle-based ETLs. The morphologies and chemical compositions of the L-ZnO ETLs varied with the annealing conditions. These factors, in turn, had a marked effect on the charge-transfer characteristics at the L-ZnO/PbS interfaces of the DH-QDSCs. The power conversion efficiency (PCE) of the DH-QDSCs using the optimized L-ZnO films as ETLs was 3.93%, with the fill factor (FF) being 0.60, whereas the PCE of the cells using the ZnO nanoparticle-based films was 1.62%, with the FF being 0.53. Thus, the sol–gel-derived L-ZnO films, which could be fabricated using a simple, low-temperature, solution-based process, exhibited desirable performance as ETLs in DH-QDSCs.