Oriented Crystallization of Mixed‐Cation Tin Halides for Highly Efficient and Stable Lead‐Free Perovskite Solar Cells

Abstract

As the most promising lead‐free branch, tin halide perovskites suffer from the severe oxidation from Sn2+ to Sn4+, which results in the unsatisfactory conversion efficiency far from what they deserve. In this work, by facile incorporation of methylammonium bromide in composition engineering, formamidinium and methylammonium mixed cations tin halide perovskite films with ultrahighly oriented crystallization are synthesized with the preferential facet of (001), and that oxidation is suppressed with obviously declined trap density. MA+ ions are responsible for that impressive orientation while Br‐ ions account for their bandgap modulation. Depending on high quality of the optimal MA0.25FA0.75SnI2.75Br0.25 perovskite films, their device conversion efficiency surges to 9.31% in contrast to 5.02% of the control formamidinium tin triiodide perovskite (FASnI3) device, along with almost eliminated hysteresis. That also results in the outstanding device stability, maintaining above 80% of the initial efficiency after 300 h of light soaking while the control FASnI3 device fails within 120 h. This paper definitely paves a facile and effective way to develop high‐efficiency tin halide perovskites solar cells, optoelectronic devices, and beyond.

Suppression of Nonradiative Recombination by Vacuum‐Assisted Process for Efficient Lead‐Free Tin Perovskite Solar Cells

“…have further promoted the PCE to 9.31% using FA 0.75 MA 0.25 SnI 3 by introducing Br to inhibit oxidation and passivate defects. [ 41 ] Nakamura et al. have added a dihydropyrazine derivative reacted with SnF 2 additive to boost the PCE up to 11.5%.…”

Stable tin perovskite solar cells developed via additive engineering

“…This allows for the reduction of Sn vacancies from Sn 4+ to Sn 2+ via a comproportionation reaction by metallic tin [30,31]. Long-chain ammonium cations such as phenylethylammonium, butylammonium, and ethylammonium have also been used to form two-and three-dimensional hierarchy structures that protect tin perovskites from oxidation and passivate the trap states [32][33][34][35][36][37][38][39][40][41]. It has also been reported that the addition of some small organic molecules or polymers, such as trimethylamine [42], CH 3 NH 3 I•3CH 3 NH 2 amine complex [43], the potassium salt of hydroquinone sulfonic acid [44], 8-hydroxyquinoline [45], liquid formic acid [46], pentafluorophenoxyethylammonium iodide [47], or poly(vinyl alcohol) [48] can improve the crystallinity and reduce the defects caused by oxidation, thereby enhancing the stability of the resulting tin perovskite.…”

Recent progress toward highly efficient tin‐based perovskite (ASnX3) solar cells

“…As a result, the corresponding device based on FA 0.75 MA 0.25 SnI 2.75 Br 0.25 shows the PCE of 9.31% compared to 5.02% of the FASnI 3 based control device. [ 194 ] Compared with MASnI 3 and FASnI 3 , FA 0.75 MA 0.25 SnI 3 shows outstanding charge injection property at the perovskite/TiO 2 interface and effectively interfacial charge separation to free carriers, confirmed by high PL quenching efficiency and short PL lifetimes originating from the largest ΔΦ found at FA 0.75 MA 0.25 SnI 3 /TiO 2 interface (Figure 20). [ 190 ] In the view of electronic potential, as more photogenerated electrons are extracted by the ETL under illumination, the surface potential is lifted by excess holes in FA 0.75 MA 0.25 SnI 3 perovskite layer.…”

“…[ 38 ] (MASnBr 3−3 x Cl 3 x ), Ref. [ 194 ] (MA 0.25 FA 0.75 SnI 2.75 Br 0.25 ), Ref. [ 68 ] (FASnI 0.75 Br 0.25 ) and Ref.…”