Composition manipulation boosts the efficiency of carbon-based CsPbI₃ perovskite solar cells to beyond 14%

The inorganic CsPbI₃ perovskite obtained from dimethylammonium iodide (DMAI)-related strategies have greatly promoted the development of CsPbI₃ perovskite solar cells (PSCs). However, deeper understandings are urgently needed to further enhance device performance. Herein, the crystallization processes of DMAI-based strategy are systematically studied and some new understandings are proposed. During annealing, β-phase-like CsPbI₃ is first formed and then gradually transits to γ-phase-like structure. DMA ions tend more to form DMAPbI₃ in the system, implying the amount of alloyed DMA ions in CsPbI₃ would be very limited. In addition, the pre-generated Cs₄PbI₆ plays an important role in stabilizing CsPbI₃ perovskite phase at low temperature. These findings help us to finely manipulate film composition, and the quality of CsPbI₃ film is substantially improved after simultaneously suppressing the formation of δ-CsPbI₃, minimizing DMAPbI₃ residual and generating PbI₂ passivator. More promisingly, the carbon-based CsPbI₃ PSCs without hole transporter achieve a record efficiency of 14.6%.