“…However, the toxicity caused by lead has always pushed people to seek lead-free perovskites considering environment-friendly applications. Many researchers investigate a lot of low-toxic or nontoxic inorganic perovskite materials, , so Ca(II), Bi(III), Sr(II), Sn(II), and Ge(II) cations were used to replace Pb cations. − Among them, Sn-based perovskites have the potentially ideal electronic and optical properties that are even better than those of Pb-based perovskite due to its band gap close to the optimal one (≈1.3 eV), strong light absorption, and good carrier mobility. − In addition, the controllability of Sn content in CsSnI 3 enables it to be used not only as a light-absorbing layer but also as a hole transport material for lead-free perovskite solar cells. ,− However, the thermal instability and thermodynamically favorable antisite defect Sn I are the main reasons limiting the PCE of inorganic Sn-based perovskites. − Compared with inorganic Pb/Sn-based perovskites, Ge-based perovskites show different structural and electronic properties, especially its defect physics: the antisite defects will not dominate during fabrication. , Under Ge-rich/I-rich conditions, the formation energies of Ge and I vacancies are relatively low and CsGeI 3 is a p-type direct band gap semiconductor . But unfortunately, the I vacancy in CsGeI 3 is a deep electron trap under I-poor conditions, which obviously limits electron migration, thereby affecting the V OC of PSC. , In order to improve the photovoltaic performance of inorganic perovskite devices, researchers performed Sn and Ge hybridization to obtain a CsSn 0.5 Ge 0.5 I 3 perovskite, a promising lead-free light-absorbing material (LAM).…”