Reduced Graphene Oxide/CZTS_xSe_1‐x Composites as a Novel Hole‐Transport Functional Layer in Perovskite Solar Cells

Abstract

Exploiting lower cost and more stable hole-transport materials to replace spiro-OMeTAD is a hot topic in the research field of perovskite solar cells (PSCs). This work exploits a novel holetransport composite containing reduced graphene oxides (RGO) and Cu 2 ZnSn(SSe) 4 (CZTS x Se 1-x ) by a green sol-gel method for efficient perovskite solar cells. The composition and crystalline structure of CZTS x Se 1-x were examined by Raman and X-ray photoelectron spectroscopy as well as by X-ray diffraction measurements. Compared with a pristine RGO hole-transport layer (HTL), the PSC with RGO/CZTS x Se 1-x composite shows an improved photovoltaic performance and enhanced stability. A maximum power conversion efficiency (PCE) of 10.08 % and an enhanced stability were obtained for the cell with the RGO/ CZTS 0.5 Se 0.5 composite. Moreover, only 14 % efficiency reduction ratio was observed for the device stored in air at room temperature after 500 hours without encapsulation. In addition, the different S/Se ratios of CZTS x Se 1-x showed distinct photovoltaic properties of the PSCs, which is attributed to the change of energetic structures, confirmed by electrochemical characterizations.

Applications of Ceramic/Graphene Composites and Hybrids

“…High-efficiency PSC (PCE 18%) was reported in 2016 for a cell with a TiO 2 /graphene composite electrode combined with a GO interlayer [ 67 ]. Graphene composites can be found as part of the conductive electrodes or as a carrier transporting material as in hole transport layer (HTL) [ 68 ] or as an electron transport layer (ETL), normally in composites with binary and ternary metal oxides enhancing the electronic transfer rate [ 69 ] and also reducing carrier recombination rate. More recently, graphene sheets have also been introduced within the active material layer to improve transport properties and chemical stability [ 70 , 71 ].…”

Recent Development in Earth-Abundant Kesterite Materials and Their Applications

“…Recently, new studies have explored co-using CZTS HTLs with carbon nanostructures. Nan et al fabricated composite reduced graphene oxide and CZTSSe through an environmentally friendly sol-gel method [79]. PCSs with composite RGO/Cu 2 ZnSn(S 0.5 Se 0.5 ) 4 HTLs showed 10.08% efficiency.…”

Effect of Zn/Sn Ratio on Perovskite Solar Cell Performance Applying Off-Stoichiometric Cu2ZnSnS4/Carbon Hole-Collecting Electrodes

“…The nontoxic earth-abundant CZTS semiconductor featured by suitable optoelectrical properties, thermal stability, facile and low-cost synthesis, and band-gap tunability has also been investigated as an HTM in n–i–p and p–i–n structured PSCs, as well as in common applications as a light absorber. − Figure c illustrates the body of these research by different groups in the literature (more details in the Supporting Information, Table S1 and Figure S1). OLAM-capped NPs and OLAM-free NPs are two categorizations for CZTS-based HTMs that have been used in PSCs by different methods of synthesis.…”

“…It is worth noting that all of these investigations have been mostly performed for the MAPbI 3 single cation absorber layer. Different morphologies and sizes (QDs, NPs, and macroporous), , different anionic ratios (S/Se), , ligand-engineered CZTS NPs, ligand-free CZTS NPs dispersed in 1-hexanethiol, different crystalline phases, and CZTS-based composites ,,, were applied as HTMs in PSCs. The highest efficiency of 17.71% was reported by Cao et al in 2020 for the n–i–p structure using ligand-free CZTS NP HTM and the FAPbI 3 absorber layer with a small active area of 0.04 cm 2 .…”