Tandem solar cells stack a perovskite layer, which absorbs the high-energy blue portion of sunlight, on top of silicon, which captures the red, and so promise efficiencies beyond what silicon alone can deliver. A group led by Erkan Aydin at LMU has now demonstrated a perovskite-silicon tandem cell with an efficiency of 31.4 per cent on industrially relevant textured silicon, the first such cell produced entirely in the Munich region.
The gain came from rethinking the self-assembled monolayer, a molecular film only nanometres thick that ferries charge into the collection layers. Conventional molecules with simple alkyl chains aggregate unevenly on pyramidally textured silicon, so the team designed a new molecule that packs densely on rough surfaces, improving charge transport and interface passivation. A piece of serendipity helped: bromine-containing impurities in a commercial precursor turned out to neutralise interface defects, and the researchers deliberately blended brominated and non-brominated molecules to lock in the benefit.
Published in Joule with partners in Shenzhen, Hong Kong and Saudi Arabia, the cells also showed improved stability over extended testing, with the densely packed molecular layer protecting the critical interface. The team is now running accelerated ageing tests under realistic environmental conditions and adapting the technology for satellites in low Earth orbit, where lightweight, radiation-tolerant and high-performance photovoltaics are an increasingly sought-after commodity for the space industry.