Importance of Reducing Vapor Atmosphere in the Fabrication of Tin-Based Perovskite Solar Cells

Abstract

Tin-based halide perovskite materials have been successfully employed in lead-free perovskite solar cells, but the tendency of these materials to form leakage pathways from p-type defect states, mainly Sn and Sn vacancies, causes poor device reproducibility and limits the overall power conversion efficiencies (PCEs). Here, we present an effective process that involves a reducing vapor atmosphere during the preparation of Sn-based halide perovskite solar cells to solve this problem, using MASnI, CsSnI, and CsSnBr as the representative absorbers. This process enables the fabrication of remarkably improved solar cells with PCEs of 3.89%, 1.83%, and 3.04% for MASnI, CsSnI, and CsSnBr, respectively. The reducing vapor atmosphere process results in more than 20% reduction of Sn/Sn ratios, which leads to greatly suppressed carrier recombination, to a level comparable to their lead-based counterparts. These results mark an important step toward a deeper understanding of the intrinsic Sn-based halide perovskite materials, paving the way to the realization of low-cost and lead-free Sn-based halide perovskite solar cells.

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

“…Moreover, a hydrazine atmosphere can help the disperse of SnI 2 65 to improve the quality of perovskite film, as indicated by no observable agglomeration of SnI 2 from the SEM/EDS characterization (Figure 10d–i). The corresponding device displayed the best PCE (4.81%) of CsSnI 3 ‐based PSCs, which is in the meantime much higher than the SnF 2 41 modified devices (1.83%). Additionally, triethyl phosphine (TEP)63 as a soft Lewis base can form intermediate complexes with Sn 2+ species via weak coordinating interaction, which could slow down the perovskite crystallization process and improve the film morphology as well as the device performance.…”

“…As an example, hypophosphorous acid (HPA)73 ( Figure 9 a) was introduced into fabricating all‐inorganic CsSnIBr 2 ‐based mesoscopic PSCs to reduce the concentration of Sn vacancies, achieving a higher PCE of 3.0% than 1.7% of without HPA addition. Moreover, Song et al41 introduced hydrazine vapor (reducing vapor atmosphere) in the presence of SnF 2 additive into fabrication process of Sn‐based PSCs (Figure 9b). The results showed that the additional hydrazine vapor process led to significantly suppressed carrier recombination with more than 20% reduction of Sn 4+ /Sn 2+ ratios.…”

“…The best J–V curves of c) MASnI 3 , d) CsSnI 3 , and e) CsSnBr 3 . Reproduced with permission 41. Copyright 2017, ACS.…”

“…Due to the suppressed SnF 2 phase separation in the CsSnIBr 2 thin films, the highest reported PCE of ≈3.2% for the all‐inorganic Sn‐based PSCs was achieved. Likewise, hydrazine41, 65 was used not only as reducing agent to reduce the oxidization of Sn 2+ to Sn 4+ , but also as modifier asserted by Song et al41 to achieve better film morphologies for enhanced device efficiencies. Unfortunately, there was no explanation of why hydrazine could do a good job in ameliorating perovskite film morphologies.…”

“…Copyright 2016, ACS; Ge: Adapted with permission 40. Copyright 2015, RSC; Sn: Adapted with permission 41. Copyright 2017, ACS).…”