A green Bi-Solvent system for processing high-quality CsPbBr3 films in efficient all-inorganic perovskite solar cells

All-brominated inorganic perovskite CsPbBr 3 has received much attention in the field of optoelectronic applications owing to its superb stability and ease of manufacture under the ambient condition. However, the tedious process and toxic solvent are two major challenges for fabrication of CsPbBr 3 films via a multi-step deposition method . Here, we demonstrate a sustainable bi-solvent system for preparing high-quality CsPbBr 3 films in a triple-step solution-processed route, where the bi-solvent system comprises of green solvent water and ethylene glycol monomethyl ether (EGME) in place of the noxious methanol for CsBr solution. By adjusting the temperature of heat treatment and spin-coating speed, the pinhole-free, ultra-smooth and high crystallinity of CsPbBr 3 films were obtained. As a result, the CsPbBr 3 PSC prepared from the green bi-solvent system demonstrates an optimal power conversion efficiency (PCE) of 9.55%, which is one of the highest efficiencies for planar carbon-based PSCs without hole transport layer. Moreover, the all-inorganic unpacked PSCs exhibit excellent humidity stability under ambient environment for 34 days. Our result not only offers a facile and simple way to fabricate the pure-phase CsPbBr 3 films, but also alleviates the solvent toxicity during the preparation of CsPbBr 3 PSCs.