Perovskite solar cells with 18.21% efficiency and area over 1 cm2 fabricated by heterojunction engineering

Perovskite solar cells (PSCs) are promising low-cost photovoltaic technologies with high solar-to-electric power conversion efficiency (PCE). The heterojunction structure between perovskite and charge extraction layers is crucial to the photovoltaic performance of PSCs. Here, we report efficient inverted-structured PSCs with a perovskite–fullerene graded heterojunction (GHJ), in which the electron-accepting material is distributed in the perovskite layer with a gradient. This structure can enhance the PCE as it improves the photoelectron collection and reduces recombination loss, especially for the formamidinium cation-based perovskite. The conformal fullerene coating on perovskite during the GHJ deposition achieves a full coverage with reduced layer thickness, thus minimizing the resistive loss in larger sized devices. Our strategy enables the fabrication of centimetre-scale PSCs showing high efficiency with small hysteresis and good stability. A PCE of 18.21% was certified by an independent institution for cells with an aperture area of 1.022 cm2. The performance of inverted perovskite solar cells has so far lagged behind that of their normal-structure counterparts. Wu et al. fabricate an inverted perovskite–fullerene solar cell with a graded heterojunction that achieves a certified efficiency of over 18% for a cell area of 1 cm2.