Low-temperature carbon-based electrodes in perovskite solar cells

Carbon-based electrodes have been widely applied in perovskite solar cells (PSCs) because of their chemical inertness and compatibility with up-scalable techniques, signifying their solid potential for mass-production. The material scarcity and complexity of metal ore extraction further highlights that conventionally used noble metal electrodes cannot represent a sustainable option for back-contact in PSCs, while cells with carbon-based electrodes represent an excellent solution to these problems. However, their power conversion efficiencies (PCEs) still lag behind the traditionally processed cells with metal electrodes, resulting in a considerable efficiency gap. To overcome this issue, we propose the use of low-temperature carbon-based (LTCB) electrodes, which offer several key advantages in comparison to mesoscopic high-temperature treated ones: (1) larger choice of selective layers, (2) applicability to all perovskite crystallization methods, (3) compatibility with flexible substrates and (4) faster deposition process. In this review, we analyze numerous techniques to formulate the LTCB-paste and ways to deposit it on the cell stack which have been developed in order to improve the interfacial contact and electrode conductivity. Besides describing the current state-of-the-art perovskite solar cells with LTCB-electrodes, the most promising strategies to enhance the PCE of such photovoltaic (PV) devices are discussed. Overall, we emphasize that PSCs with a LTCB-electrode combine high device stability, low manufacturing costs and low environmental impact, while having options for pushing the efficiency of carbon-based PSCs closer to the record-breaking cells, all of which are vital in order to fulfill the true potential of perovskite PV.