ABSTRACT
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 Cu2ZnSnS4/carbon hole collectors in n-i-p structured PSCs, where CuInS2/carbon is applied as the reference hole collector. This composition regulation is a solution to address the challenge of composition-related defects of the Cu2ZnSnS4 (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 [2ZnCu + ZnSn] 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.
ABSTRACT
Antisolvent crystallization is known as an effective approach for the deposition of pinhole-free solution-processed perovskite layers for high-performance solar cells. Here, we introduce a modified antisolvent dripping method by adding tetra ethyl orthosilicate (TEOS) into chlorobenzene as a conventional antisolvent. Through TEOS modification, perovskite solar cells show efficiencies as high as 16% with more than 85% retention after 290 h storage at ambient conditions in comparison to 20% in pristine cells. This significant enhancement in efficiency and stability mainly related to the decrement of the density of surface defects, which is confirmed by considerably enhanced photoluminescence of perovskite layers. Also, electrochemical impedance spectroscopy results show lower charge recombination at interfaces in modified cells. Regarding the obtained results, our modified antisolvent approach is a simple and promising route to prepare high-quality perovskite layers for solar cell applications.
