The open-circuit voltage (V_OC) of cesium-based perovskite solar cells (Cs-PSCs) is severely limited by carrier recombination both in bulk and at the interface between the perovskite layer, which mainly from the increase in fabrication temperature. To improve the performance of Cs-PSCs, enhancing the quality of perovskite film and optimizing the device structure are effective strategies. Joule (IF 41.248) published a study in March 2022. Herein, the VOC is significantly promoted by constructing CsPbI₃/Cs₁-xDMAxPbI₃ bulk heterojunction (BHJ) structure that was spontaneously formed through a precisely controlled spatially selective phase transition approach.

　　It is found that the perovskite BHJ structure not only facilitates the charge separation and collection process by increasing the built-in potential, but also significantly reduces the carrier recombination loss. Importantly, a maximum V_OC of 1.23 V was obtained due to under-V_OC reduction to 0.45V. and the champion power conversion efficiency (PCE) reached 20.32% (certified PCE of 19.66%). This study shows that junction engineering will become a new strategy for high-efficiency perovskite devices.