Fast anion-exchange from CsPbI3 to CsPbBr3 via Br2-vapor-assisted deposition for air-stable all-inorganic perovskite solar cells

Nowadays, inorganic perovskites such as CsPbI3 and CsPbBr3 with excellent photoelectric property and superior thermal stability have triggered strong interest in the photovoltaic community. However, all of the inorganic perovskite absorbers reported in literatures are fabricated by the complicated solution process. Meanwhile, CsPbI3 exists serious structural phase-transition; while stable CsPbBr3 suffers solubility limitation of bromide in conventional solution route. Herein, we develop a smart Br-2-vapor-assisted chemical vapor deposition (CVD) method to realize the fast anion-exchange from CsPbI3 to CsPbBr3. With the substitution of small Br- anions, the undesirable phase-transition of CsPbI3 is heavily restrained and its structural stability is tremendously enhanced; and thus here we open a new avenue to solve the solubility issue of bromide. Consequently, CsPbBr3 all-inorganic perovskite solar cells (PSCs) with Carbon top electrode are first achieved by cost-effective CVD technology, showing a relatively high power conversion efficiency (PCE) of 5.38%. The charge transport mechanism of CsPbBr3 PSCs is correspondingly elucidated in-depth. We find that the interface of TiO2 and CsPbBr3 might be the root cause of hysteresis phenomenon, while another interface between Carbon and CsPbBr3 is not a rectifying contact but only increases the ohmic resistance of electrode. Moreover, our PSCs demonstrate a good long-term stability and give similar to 90% of initial efficiencies after exposure to air for 21 days.