Perspective on Predominant Metal Oxide Charge Transporting Materials for High-Performance Perovskite Solar Cells

Mriganka Singh,Chih Wei Chu,Annie Ng

doi:10.3389/fmats.2021.655207

Abstract

Nowadays, the power conversion efficiency of organometallic mixed halide perovskite solar cells (PSCs) is beyond 25%. To fabricate highly efficient and stable PSCs, the performance of metal oxide charge transport layers (CTLs) is one of the key factors. The CTLs are employed in PSCs to separate the electrons and holes generated in the perovskite active layer, suppressing the charge recombination rate so that the charge collection efficiency can be increased at their respective electrodes. In general, engineering of metal oxide electron transport layers (ETLs) is found to be dominated in the research community to boost the performance of PSCs due to the resilient features of ETLs such as excellent electronic properties, high resistance to thermal temperature and moisture, ensuring good device stability as well as their high versatility in material preparation. The metal oxide hole transport layers in PSCs are recently intensively studied. The performance of PSCs is found to be very promising by using optimized hole transport materials. This review concisely discusses the evolution of some prevalent metal oxide charge transport materials (CTMs) including TiO2, SnO2, and NiOx, which are able to yield high-performance PSCs. The article begins with introducing the development trend of PSCs using different types of CTLs, pointing out the important criteria for metal oxides being effective CTLs, and then a variety of preparation methods for CTLs as employed by the community for high-performance PSCs are discussed. Finally, the challenges and prospects for future research direction toward scalable metal oxide CTM-based PSCs are delineated.

Highlights

In the 21st century, we are living in an energy-driven world
The widespread use of solar energy requires the development of cost-effective and highperformance photovoltaics (PVs) for efficient energy conversion from solar to electric energy
A number of challenges such as device long-term stability, hysteresis effect, toxicity of lead, and scalable difficulties still remain in the community (Djurišicet al., 2016; Djurišicet al., 2017; Li et al, 2018; Li et al, 2020)

Summary

Introduction

In the 21st century, we are living in an energy-driven world. Sustainability in energy generation is one of the most challenging issues to satisfy the ever-increasing energy demands. The recently announced record power conversion efficiency (PCE) values of single-junction PSCs and perovskite-based monolithic tandem devices are 25.5 and 29.5%, respectively (The National Renewable Energy Laboratory [NREL], 2021), which outperform other thin-film PV technologies (e.g., CIGS and CdTe) and are comparable to well-established solar technologies such as crystalline silicon photovoltaics (PCE ∼26.1%). Such impressive device efficiency of PSCs is owing to inherent perovskite properties such as large absorption coefficients, adjustable bandgaps, low exciton binding energy, large carrier diffusion lengths, and high charge mobilities (Xing et al, 2013; Wang et al, 2015). Some comprehensive review papers on those topics have been published (Jiang et al, 2018; Sajid et al, 2018; Ouyang et al, 2019; Hanmandlu et al, 2020; Hu et al, 2020a; Zhou et al, 2020)

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