Lead‐Free Inverted Planar Formamidinium Tin Triiodide Perovskite Solar Cells Achieving Power Conversion Efficiencies up to 6.22%

Abstract

Efficient lead (Pb)-free inverted planar formamidinium tin triiodide (FASnI ) perovskite solar cells (PVSCs) are demonstrated. Our FASnI PVSCs achieved average power conversion efficiencies (PCEs) of 5.41% ± 0.46% and a maximum PCE of 6.22% under forward voltage scan. The PVSCs exhibit small photocurrent-voltage hysteresis and high reproducibility. The champion cell shows a steady-state efficiency of ≈6.00% for over 100 s.

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

“…133, 138 Accordingly, FASnI 3 ‐based PSCs exhibited much better reproducibility as compared to MASnI 3 ‐based devices 138. In 2016, Liao et al56 reported a PCE of 6.22% based on FASnI 3 PSCs with high reproducibility, which is one of the best efficiencies among Sn‐based PSCs (Figure 3d,e). Very recently, Shi et al139 studied the phenomenon theoretically and found that the antibonding coupling between Sn‐s and I‐p is weaker in FASnI 3 than in MASnI 3 due to the larger ionic size of FA, leading to higher formation energies of Sn vacancies in FASnI 3 .…”

“…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.…”

“…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. The fresh spin‐coated films showed a reddish intermediate state after dripping with diethyl ether, which might be crucial for the good film morphology, in contrast to chlorobenzene and toluene‐based antisolvents, which led to black films immediately (Figure 11e–h).…”

“…FASnI 3 films deposited on PEDOT: PSS by different anti‐solvent drippings: e) no dripping, f) chlorobenzene, g) toluene, and h) diethyl ether. Reproduced with permission 56. SEM images of FASnI 3 with i) diethyl ether and j) chlorobenzene as antisolvent.…”