A New Approach to Stabilise Perovskite Solar Cells Without Lead - Prof Lam Yeng Ming & Prof Sum Tze Chien (SPMS)

We are pleased to share that Professor Lam Yeng Ming and her team have been featured in the news for having discovered a way to manufacture non-toxic metal-based capping layers for perovskite solar cells. 

The less environmentally damaging method involves replacing the traditional capping layer, which would result in the production of toxic lead when perovskites decompose or used for an extended time, with a zinc-based capping layer.

The researchers, led by Professor Sum Tze Chien (SPMS) and Professor Lam Yeng Ming (MSE), used the full precursor (FP) solution method to synthesise a capping layer that does not contain lead. Using the FP method, they coated the perovskites with solutions containing metal halide salts – compounds made of metal and elements that include chlorine, fluorine and iodine – and phenethylammonium iodide (PEAI) that is commonly applied to perovskites to improve the performance of perovskite solar cells. They found that a zinc-based compound PEA₂ZnX₄ synthesised using the method was the most effective capping material amongst the other materials tested. Unlike the typical approach of using the half precursor (HP) method to fabricate the capping layer, there is no need to draw lead ions up from the underlying perovskite layer to form this protective capping layer when the FP method is used, hence paving the way for the use of non-toxic metals in the capping layer.

The team’s fabricated solar cell was found to be as effective at converting sunlight to energy as conventional perovskite solar cells. In experiments with light that simulated sunlight, the solar cell could convert 24.1 percent of the light captured to electricity, close to the highest efficiency achieved by perovskite solar cells so far. Their prototype also demonstrated good reproducibility, with an average light conversion rate of almost 23 percent over 103 cells. It had a long lifespan, maintaining more than 90 percent of its ability to convert light into electricity for more than 1,000 hours of operation at full capacity.

Three-dimensional/low-dimensional perovskite solar cells afford improved efficiency and stability. The design of low-dimensional capping materials is constrained to tuning the A-site organic cation, as Pb²⁺ and Sn²⁺ are the only options for the metal cation. Here we unlock access to a library of low-dimensional capping materials with metal cations beyond Pb²⁺/Sn²⁺ by processing a full precursor solution containing both metal and ammonium halides. This enables easier synthetic control of the low-dimensional capping layer and greater versatility for low-dimensional interface engineering. We demonstrate that a zero-dimensional zinc-based halogenometallate (PEA₂ZnX₄; PEA = phenethylammonium, X = Cl/I) induces more robust surface passivation and stronger n–N isotype three-dimensional/low-dimensional heterojunctions than its lead-based counterpart. We exhibit p–i–n solar cells with 24.1% efficiency (certified 23.25%). Our cells maintain 94.5% initial efficiency after >1,000 h of operation at the maximum power point. Our findings expand the material library for low-dimensional interface engineering and stabilization of highly efficient three-dimensional/low-dimensional perovskite solar cells. 

(DOI: https://doi.org/10.1038/s41560-023-01204-z)

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