Highly efficient and cost-effective carbon paper electrode for inverted perovskite solar cells

Perovskite solar cells (PSCs) are among the most promising photovoltaic technologies, with their power conversion efficiency (PCE) rising from 3.8 % in 2009 to 26.95 % in 2025. However, their commercialization remains hindered by challenges such as the high cost of noble metal back-contacts. Finding affordable alternatives for back-contacts is therefore a key research focus. Carbon-based materials have attracted growing interest due to their abundance, low cost, chemical stability, electronic conductivity, sustainability, and suitability for large-scale deposition. In this work, the effective use of carbon paper (CP) as a back-contact in inverted PSCs was demonstrated. To facilitate charge extraction, a thin metal interlayer, consisting of ca. 7 nm of gold (Au) or silver (Ag), was introduced between the electron transport layer and the CP. Five different CPs were tested, yielding PCEs of 6.35 % and 8.65 % for devices incorporating 7 nm Au + CP and 7 nm Ag + CP, respectively. To further enhance charge extraction, the impact of a thermally evaporated molybdenum trioxide-doped gold (7 nm Au:MoO₃) was explored, resulting in enhanced interface quality and reduced recombination losses. A champion device with a PCE of 15.6 % was achieved, making one of the highest reported values for carbon-based inverted PSCs.