Toward durable all-inorganic perovskite solar cells: from lead-based to lead-free

Abstract

The emergence of organic-inorganic metal halide perovskite solar cells (PSCs) has attracted extensive attentions across the photovoltaic (PV) community due to their fast-growing power conversion efficiency from 3.8% to 26.7% in only 15 years. However, these organic-inorganic hybrid compounds suffer from inferior long-term operational stability under thermal and light stress, given the fragile hydrogen bonds between organic cations and inorganic slabs. This motivates the exploration of more robust all-inorganic alternatives against external stimuli, by substituting inorganic cesium (Cs) cations for volatile organic cations. Despite reinforced ionic interaction between Cs cations and metal halide frameworks, these Cs-based all-inorganic perovskites tend to undergo spontaneous phase transition from photoactive black phases to non-perovskite yellow phases at room temperature, significantly deteriorating their optoelectronic performance. Thus, tremendous efforts have been made to stabilizing the black phase of CsPbI3, while the phase instability issue of its tin-based analogue of CsSnI3 has not been resolved yet. This perspective summarizes the empirical advances on stabilizing the metastable phases of CsPbI3, aiming at providing useful guidelines to accelerate the development of phase-stable CsSnI3 for durable lead-free PV applications. Finally, the remaining challenges and future research opportunities are outlined, providing a roadmap to realizing efficient and durable all-inorganic perovskite solar cells towards practical applications.