| Summary: | Perovskite solar cells have exhibited astonishing photoelectric conversion efficiency and have shown a promising future owing to the tunable content and outstanding optoelectrical property of hybrid perovskite. However, the devices with planar architecture still suffer from huge <i>V</i><sub>oc</sub> loss and severe hysteresis effect. In this research, Guanidine hydrobromide (GABr) post-treatment is carried out to enhance the performance of MAPbI<sub>3</sub> n-i-p planar perovskite solar cells. The detailed characterization of perovskite suggests that GABr post-treatment results in a smoother absorber layer, an obvious reduction of trap states and optimized energy level alignment. By utilizing GABr post-treatment, the <i>V</i><sub>oc</sub> loss is reduced, and the hysteresis effect is alleviated effectively in MAPbI<sub>3</sub> solar cells. As a result, solar cells based on glass substrate with efficiency exceeding 20%, <i>V</i><sub>oc</sub> of 1.13 V and significantly mitigated hysteresis are fabricated successfully. Significantly, we also demonstrate the effectiveness of GABr post-treatment in flexible device, whose efficiency is enhanced from 15.77% to 17.57% mainly due to the elimination of <i>V</i><sub>oc</sub> loss.
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