Out‐of‐Glovebox Integration of Recyclable Europium‐Doped CsPbI3 in Triple‐Mesoscopic Carbon‐Based Solar Cells Exceeding 9% Efficiency

CsPbI3 perovskites are attracting huge interest for their inorganic structure and thanks to a bandgap of 1.69–1.78 eV that makes them suitable for application in tandem solar cells with silicon. Herein, all-inorganic hole-transporting-layer (HTL)-free carbon-based CsPbI3 perovskite solar cells (mC-PSCs) are fabricated, for the first time, by infiltrating CsPbI3 solutions enriched with precursors of Europium into triple mesoscopic structures with mesoporous (mp) materials (mp-TiO2/mp-ZrO2/mp-Carbon). The use of Europium is beneficial to mitigate lattice defect formation during the reaction. Drop casting of the solution is done in air and the black γ-phase formation is promoted under dynamic nitrogen flow during high-temperature annealing (350 °C), which is preferred to low-temperature treatments to maximize perovskite phase stability. The preparation protocol entrusts the devices with the best power conversion efficiencies (PCEs) of 9.2% and 5.2% using EuI2 and EuCl3, respectively. Recorded PCE is considerably lower (<2%) in the reference devices prepared without Europium. In addition, the Eu-based devices are recycled to reconvert the photo-inactive yellow δ-phase into the photo-active black γ-phase with the devices losing only ≈10% of the efficiency of the original device. Thus, it is demonstrated that mC-PSCs recycling is feasible by exploiting the special feature of the high-temperature black γ-phase-reversibility.