Effect of Zn/Sn Ratio on Perovskite Solar Cell Performance Applying Off-Stoichiometric Cu 2 ZnSnS 4 /Carbon Hole-Collecting Electrodes.

Low-cost inorganic hole-transporting materials (HTMs) accompanied by a printable carbon electrode is an efficient approach to address the limitation of material cost of perovskite solar cells (PSCs) and get this technology closer to commercialization. The present work is focused on optimizing the Zn/Sn ratio of Cu 2 ZnSnS 4 /carbon hole collectors in n-i-p structured PSCs, where CuInS 2 /carbon is applied as the reference hole collector. This composition regulation is a solution to address the challenge of composition-related defects of the Cu 2 ZnSnS 4 (CZTS) material. The Zn/Sn ratio was tuned by the initial proportion of the zinc precursor during the nanoparticle (NP) synthesis using a heating-up procedure. It was found that the enhancement of the Zn/Sn ratio leads to a gradual increase of the optical band gap. More importantly, an increased density of B-type defect clusters [2Zn Cu + Zn Sn ] is confirmed using Raman results. Additionally, results from the cyclic voltammetry measurement show that by increasing the Zn/Sn value, the highest occupied molecular orbital (HOMO) of HTM is pulled down. These data match the upward trend of photovoltage. CZTS HTM with an optimal Zn/Sn ratio of 1.5 has a compatible energy level, along with the features of uniform and smooth coverage. The best efficiency of about 14.86% was obtained for optimal CZTS/carbon-based PSCs, which reaches from 14.86 to 15.49% after 25 days of aging.