The quest to improve upon the efficiency of solar cells is never-ending. At the moment, silicon-based PERC (Passivated Emitter and Rear Contact) photovoltaic cells are considered the most efficient on the market and set the standard, with a maximum PCE (Power Conversion Efficiency) of around 23 percent.

But a joint effort from the Helmholtz Centre Berlin (HZB) and the Institute for Solar Energy Research in Hamelin (ISFH) has demonstrated that the performance of silicon PERC cells can be enhanced with the addition of a perovskite cell “topper”. Perovskites are a promising new class of photovoltaics based on crystalline structures that have a higher conversion efficiency and are easier to produce than silicon; however, the technology is still nascent.

The new tandem cells, which combine silicon and perovskite, are able to convert a broader spectrum of sunlight into electricity more efficiently than just single cells. What the scientists are proposing therefore is a “perovskite tandem upgrade” for PERC systems – which as the “workhorse” of photovoltaics account for 50 percent of global market share.

The team at ISFH made sure the silicon backsides of the tandem cells were industry compatible, while a POLO contact was used on the front of the wafer – also widely compatible. The HZB team have already developed a record-breaking tandem cell on “n-type silicon heterojunction cells” and the new PERC/POLO tandem cells use a similar technology.

The efficiency of the tandem cell is currently at 21.3 percent – still less than an optimised PERC single cell – however, the experts are confident that with further layer and process optimisation, the next iteration could achieve 29.5 percent – significantly higher than PERC cells.

The project is funded by the Federal Ministry of Economics and Climate Action.