Tailoring Crystal Structure of FA 0.83 Cs 0.17 PbI 3 Perovskite Through Guanidinium Doping for Enhanced Performance and Tunable Hysteresis of Planar Perovskite Solar Cells

Abstract Current–voltage hysteresis of perovskite solar cells (PSCs) has raised the concern of accurate performance measurement in practice. Although various theories have been proposed to elucidate this phenomenon, the origin of hysteresis is still an open question. Herein, the use of guanidinium cation (Gu + )‐dopant is demonstrated to tailor the crystal structure of mixed‐cation formamidinium‐cesium lead triiodide (FA 0.83 Cs 0.17 PbI 3 ) perovskite, resulting in an improved energy conversion efficiency and tunable current–voltage hysteresis characteristic in planar solar cells. Particularly, when the concentration of Gu‐dopant for the perovskite film increases, the normal hysteresis initially observed in the pristine PSC is first suppressed with 2%‐Gu‐dopant, then changed to inverted hysteresis with a higher Gu‐dopant. The hysteresis tunability behavior is attributed to the interplay of charge/ion accumulation and recombination at interfaces in the PSC. Furthermore, compared to the cell without Gu + ‐dopant, the optimal content of 2% Gu + ‐dopant also increases the device efficiency by 14%, reaching over 17% under one sun illumination.