TiO₂–ZnS Cascade Electron Transport Layer for Efficient Formamidinium Tin Iodide Perovskite Solar Cells

Abstract

Achieving high open-circuit voltage (V) for tin-based perovskite solar cells is challenging. Here, we demonstrate that a ZnS interfacial layer can improve the V and photovoltaic performance of formamidinium tin iodide (FASnI) perovskite solar cells. The TiO-ZnS electron transporting layer (ETL) with cascade conduction band structure can effectively reduce the interfacial charge recombination and facilitate electron transfer. Our best-performing FASnI perovskite solar cell using the cascaded TiO-ZnS ETL has achieved a power conversion efficiency of 5.27%, with a higher V of 0.380 V, a short-circuit current density of 23.09 mA cm, and a fill factor of 60.01%. The cascade structure is further validated with a TiO-CdS ETL. Our results suggest a new approach for further improving the performance of tin-based perovskite solar cells with a higher V.

Lead‐Free Hybrid Perovskite Absorbers for Viable Application: Can We Eat the Cake and Have It too?

“…On the other hand, FA‐based hybrid perovskites have better solubility than all‐inorganic perovskites. According to the summary in Table 1, no spin coating with solvent‐engineering was used in Cs‐based perovskites due to their poor solubility, but in the case of FA counterparts, most good results28, 56, 57 originated from solvent‐engineering resulted in excellent morphology. Second, mixing organic cations at A position seems an effective method to improve devices performance.…”

“…The author has concluded that the SnF 2 cannot only improve interfacial energy alignment but also increase stability to electron beam damage. Nowadays, most Sn‐based perovskites films prepared by solution deposition need additional SnF 2 to get good performance,47, 48, 57, 58, 73 including the recent (FA) 0.75 (MA) 0.25 SnI 3 based PSCs with the highest PCE of 8.12% 56. Additionally, Ma et al134 claimed that SnF 2 as the inhibitor of Sn 2+ oxidation in the MASnI 3 film could increase the fluorescence lifetime up to 10 times and give longer carrier diffusion lengths >500 nm, compared with pristine MASnI 3 films.…”

“…Chlorobenzene,161 as a common antisolvent applied in lead‐based PSCs, was adopted by Zhang et al60 as antisolvent to achieve a dense FASnI 2 Br film giving a device PCE of 1.72%. As an antisolvent, diethyl ether seems to work better than chlorobenzene in improving the morphology of Sn‐based perovskites 56, 57. For example, recently, Liao et al56 used diethyl ether as an antisolvent in solvent engineering process to synthesize uniform and pinhole‐free FASnI 3 perovskite thin films.…”

“…Champion PCE of 6.22% and high reproducibility were achieved based on FASnI 3 PSCs, showing good stability for 30 d (maintaining 85% of its initial efficiency stored in dark and glove box) with encapsulated cells. Later, Ke et al57 also used diethyl ether as antisolvent to prepare uniform FASnI 3 perovskite films with high surface coverage on the neat TiO 2 and TiO 2 –ZnS substrates. They pointed out that the use of diethyl ether as an antisolvent in fabrication procedure was advantageous to inhibiting phase separation caused by excess SnF 2 .…”

“…SEM images of FASnI 3 with i) diethyl ether and j) chlorobenzene as antisolvent. Reproduced with permission 57. Copyright 2016, ACS.…”