Unlocking Voltage Potentials of Mixed‐Halide Perovskite Solar Cells via Phase Segregation Suppression

Abstract Wide bandgap ( E g ) mixed‐halide perovskite has attracted much attention for applications in photovoltaic devices. However, devices featuring this type of perovskite are often subject to a large voltage deficit due to the occurrence of phase segregation, which limits the relevant devices’ access to high performances. Here, the correlation of the phase segregation and voltage losses for wide‐ E g mixed‐halide perovskite solar cells (PSCs) is clarified by experiments and simulations. Taking 1.67 eV E g mixed‐halide perovskite as an example, it is confirmed experimentally that the control devices produce a poor physical morphology, a locally widened E g , and an inferior electrical response. By suppressing the phase segregation, the open‐circuit voltage ( V oc ) can be boosted from 1.15 to 1.20 V, which is a high value for the 1.67 eV E g mixed‐halide PSCs. An electrical simulation of phase segregation reveals that the performance degeneration can be attributed to the bulk recombination due to the energy level mismatch of the varied E g s. Moreover, a theoretical perspective is produced to expatiate on the strategies for the high V oc of wide‐ E g PSCs. This study brings deep guidance to unlock the potential for high‐performance mix‐halide PSCs.