Tin perovskite solar cells with >1,300 h of operational stability in N ₂ through a synergistic chemical engineering approach

Summary

Despite the promising properties of tin-based halide perovskites, one clear limitation is the fast Sn ⁺² oxidation. Consequently, the preparation of long-lasting devices remains challenging. Here, we report a chemical engineering approach, based on adding Dipropylammonium iodide (DipI) together with a well-known reducing agent, sodium borohydride (NaBH ₄), aimed at preventing the premature degradation of Sn-HPs. This strategy allows for obtaining efficiencies (PCE) above 10% with enhanced stability. The initial PCE remained unchanged upon 5 h in air (60% RH) at maximum-power-point (MPP). Remarkably, 96% of the initial PCE was kept after 1,300 h at MPP in N ₂. To the best of our knowledge, these are the highest reported values for Sn-based solar cells. Our findings demonstrate a beneficial synergistic effect when additives are incorporated, highlight the important role of iodide in the performance upon light soaking, and, ultimately, unveil the relevance of controlling the halide chemistry for future improvement of Sn-based perovskite devices.

Graphical abstract

Highlights

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  Highly efficient and long-lasting unencapsulated Sn-perovskite (Sn-HPs) solar cells

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  Synergistic chemical engineering approach for highly efficient and durable Sn-HPs

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  Elucidation of the photo-electrochemical mechanisms involved in Sn-HPs solar cells

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  Relevance of halide photochemistry in the performance of Sn-HPs solar cells

Context & scale

Despite the unprecedented achievements that solar cells based on lead perovskites have experienced in the last decades, they still suffer from essential limitations. Toxicity has been considered a handicap since the commencement of their exploitation. The stability of halide perovskites is far from being comparable to that of silicon. In addition, the photo-electrochemistry that determines their performance, the degradation paths, and the role of the additives employed is not fully understood. Tin-based perovskites alleviate the toxicity associated with lead, and we have developed a synergetic chemical strategy to enhance the performance of devices, giving special emphasis to extending the operational stability. Remarkably, our findings point to the significance of the halides’ chemistry in outlining the device's performance, as well as contribute to unveiling mechanistic details that determine the photo-electrochemical processes that rule the operating principles and degradation reactions.

Abstract

Tin-based halide perovskites are promising candidates for the development of highly efficient and low-cost photovoltaics based on low-toxicity materials. Yet, the performance of Sn-HPs solar cells is far below that of other technologies. This work focuses on enhancing the photoconversion efficiencies and extending the operational lifetime of the devices through the beneficial synergy provided by the incorporated additives. Furthermore, crucial mechanistic details that determine the performance of the devices are provided with the aim of bringing this technology one step forward.