Tin Oxide Replaces Scarce Indium in 31%-Efficient Solar Cell Breakthrough

One of the biggest obstacles to scaling next-generation solar panels has been the cost of a little-known metal called indium. Now, an international team of researchers has found a way to build highly efficient tandem solar cells using tin oxide — a material that costs just 1% as much — without sacrificing performance.

Published in the journal Science, the breakthrough replaces indium-based transparent conductive oxides with tin oxide (SnO_x) deposited via a low-damage reactive plasma process. The result is a commercially sized perovskite-silicon tandem mini-module that achieves a certified efficiency of 31% — matching the best indium-based cells while dramatically reducing material costs.

Indium is a rare metal primarily produced as a byproduct of zinc mining. Its price volatility and supply concentration have raised concerns about the scalability of tandem solar technology, which stacks perovskite on top of silicon to capture more of the solar spectrum. The new approach, led by researchers from Monash University and international partners, uses tin — a far more abundant and widely available element.

The reactive plasma deposition (RPD) technique used to create the tin oxide layers also improved durability, with the cells retaining over 95% of their initial efficiency after more than 1,000 hours of continuous operation. The team noted that the same method can be adapted for existing manufacturing lines, meaning the technology could reach commercial production faster than entirely new cell architectures.

As solar energy becomes the fastest-growing source of electricity worldwide, breakthroughs that eliminate dependence on scarce materials are critical. The 31% efficiency mark places these indium-free cells well above the ~22% efficiency of standard silicon panels, making them attractive for utility-scale deployments where land and space are at a premium.