Methods and strategies for achieving high-performance carbon-based perovskite solar cells without hole transport materials

Perovskite solar cells (PSCs) have garnered great attention from the scientific community due to their high power conversion efficiency (PCE) achieved via low-cost and solution-processed fabrication techniques. However, their low stability has hindered their commercialization. Replacing hole transport materials (HTMs) and Au electrodes with carbon electrodes is a promising way to address the stability issues of PSCs because carbon materials are stable, inert to ion migration, and inherently water-resistant. So far, carbon-based PSCs without HTMs (C-PSCs) have seen much progress and their PCEs have been promoted to above 16%. Herein, we comb through the recent developments in designing, fabricating and optimizing high-performance C-PSCs. First, some key issues peculiar to C-PSCs in terms of the device structure and working principles of C-PSCs, which are different from those of HTM-based PSCs, are stressed. Then, the specific methods and strategies for achieving high-performance C-PSCs are summarized and discussed, which are categorized by the electron transport materials, perovskite layer and carbon electrode. Finally, an outlook is provided, with an aim to point out the promising research directions to further improve device performance and push the technology for commercialization.