Low-temperature processed natural hematite as an electron extraction layer for efficient and stable perovskite solar cells

The mixed halide perovskite solar cells (PSC) have manifested as a contender to market-dominating silicon counterparts owing to their low-temperature solution processing and high efficiency. In PSCs, the electron extraction layer (EEL) plays a vital role as it controls charge transport/extraction from the perovskite absorber layer to the EEL and also determines interfacial recombination and charge accumulation at the EEL/perovskite interface. In this work, high-purity natural hematite (alpha-Fe2O3) is reported for the first time as the EEL in triplecation perovskite (CsFAMA) solar cells. To show the cost-effectiveness of this novel EEL, the entire device fabrication process was carried out at a temperature below 150 degrees C. The optimal alpha-Fe2O3 EEL shows a mobility value of 9.5 x 10(-4) cm(-2) V-1 s(-1) and trap densities of around 2.40 x 10(16) cm(-3); the latter is close to state-of-theart SnO2 EEL (1.26 x 10(16) cm(-3)). The PSCs employing optimal EEL concentration of 10 mg/mL demonstrated a power conversion efficiency (PCE) of 13.3 %, fill factor of 68 %, and VOC of 1.03 V. X-ray diffraction studies show a high crystallinity of natural hematite whereas the photoluminescence studies show a fast carrier extraction from the perovskite to the EEL. The natural alpha-Fe2O3-based PSCs exhibited superior shelf-life stability of over 30 days due to less charge recombination and smoother CsFAMA thin film deposited over alpha-Fe2O3 EEL. The lowtemperature processed natural alpha-Fe2O3 EEL can therefore be a promising EEL material for low-cost efficient PSCs.