Tuning recombination and charge separation in a n/p/p heterojunction solar cell with CZTS, Ag3SbS3 and a carbon interlayer

Abstract

An affordable n/p/p heterojunction solar cell design that captures and converts visible to near-infrared light to deliver a high-power conversion efficiency (PCE) of ∼9.76%, is presented. In this liquid junction solar cell, an n/p-type photoanode of TiO₂/CdS/Cu₂ZnSnS₄ (CZTS) is combined with a p-type photocathode of Ag₃SbS₃/NiO/C/Ni foam. The different band gaps of the photoactive semiconductors, the favorably aligned energy levels at both photo-electrodes that suppress the undesirable recombination processes and an electrically conducting carbon interlayer with an appropriately positioned work function of 5 eV that ensures fast and efficient relay of electrons from Ni to NiO, cumulatively impart a PCE to the n/p/p heterojunction cell superior to that achieved with the stand alone p-type (Ag₃SbS₃, ∼1.6%) and n-type (CdS/CZTS, ∼7%) solar cells. The p-type conduction behavior of CZTS affords facile hole extraction from CdS and their transfer to polysulfide species and the narrow band gap of Ag₃SbS₃ QDs (∼1.46 eV) enables broad spectral utilization, thus contributing to the high PCE. The n/p/p heterojunction solar cell offers long term stability for it endures about 90 days of intermittent illumination and storage and retains ∼72% of its initial efficiency. This durability underscores its practical applicability for real-world use and this study offers a fresh perspective to develop cost effective n/p/p heterojunction cell configurations with fewer layers and without the need of lead-containing perovskites or QDs or costly Si/Ru-dyes.