Fe2O3–NiO doped carbon counter electrode for high-performance and long-term stable photovoltaic perovskite solar cells

Perovskite solar cells (PSCs) based on carbon have been viable contenders in the field of photovoltaic due to their low cost, outstanding stability in high-humidity atmospheric air, and high electrical conductivity. Also, using inexpensive counter electrodes with PSCs devoid of organic hole transport materials (OHTMs) might be one way to get around the cost problem. Herein, at first, two different metal oxide nanoparticles (Fe2O3-NPs and NiO-NPs) were synthesized by a novel and cost-effective process. Then these nanoparticles were doped in carbon paste as a hole-transporting material (HTM) to improve charge extraction, interface contact, and energy level alignment, as well as reduction of energy loss, charge recombination, and perovskite surface degradation. The photovoltaic properties of these devices were investigated. All cells showed better efficiency than the control cell, but Fe2O3–[email protected] had better performance with high hole conductivity, matched energy level, and staircase band alignment of perovskite/Fe2O3–[email protected] Fe2O3 has a higher valence band (VB) than NiO, which facilitates the holes transfer from perovskite and NiO to counter electrode and accelerates the separation of photogenerated electron–holes. The optimal device, FTO/c-TiO2/m-TiO2/perovskite/Fe2O3–[email protected], achieves a power conversion efficiency (PCE) of 13.27% without encapsulation, compared to the control device (9.49%), and has outstanding long-term stability, retaining almost 82% of its initial efficiency over 720 h. The control device, FTO/c-TiO2/m-TiO2/perovskite/C, kept 66% of the original PCE after 720 h. Therefore, the PSCs based on Fe2O3–NiO doped carbon demonstrated substantial PCE and have good stability in ambient settings, thus making them one of the least expensive PSCs to commercialize.