Carbon-based perovskite solar cells without a hole transport layer (HTL) are considered to be highly stable and of low cost. However, the deficient interface contact and inferior hole extraction capability restrict the further improvement of the device efficiency. Introducing a hole transporting layer, such as cuprous thiocyanate (CuSCN), can enhance the hole extraction ability and improve the interface contact. However, our further studies indicated that-at a certain temperature-for carbon-based solar cells, in the CuSCN layer, the diffusion of SCN- into the perovskite film would produce more interfacial defects and aggravate nonradiative recombination, thus hindering the carrier transport. We further disclosed the reasons for performance attenuation during the thermal treatment of carbon electrodes, proposed a vacuum-assisted drying process for carbon electrodes to suppress the destructive effect, and finally, achieved an enhanced efficiency for perovskite solar cells with a CuSCN inorganic HTL and screen-printable carbon electrode. Also, the unencapsulated perovskite solar cell demonstrated over 80% efficiency retention after being stored in an ambient atmosphere (45-70% relative humidity (RH)) for over 1000 h and maintained over 85% efficiency retention for 309 h of 1-sun irradiation under a continuous nitrogen flow under open-circuit conditions.
Keywords: CuSCN; carbon electrodes; ion diffusion; perovskite solar cells; vacuum-assisted drying.