High-Efficiency Double Absorber PbS/CdS Heterojunction Solar Cells by Enhanced Charge Collection Using a ZnO Nanorod Array

The device architecture of solar cells remains critical in achieving high photoconversion efficiency while affordable and scalable routes are being explored. Here, we demonstrate a scalable, low cost, and less toxic synthesis route for the fabrication of PbS/CdS thin-film solar cells with efficiencies as high as ∼5.59%, which is the highest efficiency obtained so far for the PbS-based solar cells not involving quantum dots. The devices use a stack of two band-aligned junctions that facilitates absorption of a wider range of the solar spectrum and an architectural modification of the electron-accepting electrode assembly consisting of a very thin CdS layer (∼10 nm) supported by vertically aligned ZnO nanorods on a ∼50 nm thick ZnO underlayer. Compared to a planar electrode of a 50 nm thick CdS film, the modified electrode assembly enhanced the efficiency by ∼39% primarily due to a significantly higher photon absorption in the PbS layer, as revealed by a detailed three-dimensional finite difference time-domain optoelectronic modeling of the device.