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

Abstract

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.