In view of the growing share of balance-of-system costs in solar cells, cost benefits can currently best be achieved by raising efficiency. Given the limited potential for optimisation by enhancing current technologies like the p-type Passivated Emitter and Rear Cell technology, a research project from the Institute for Solar Energy Research (ISFH) and Leibniz Universität Hannover decided to focus developing alternatives.
And they were successful: at the beginning of February, the researchers announced they had achieved a 26.10 +/-0.31% efficiency under one sun. This high degree of efficiency – a world record for p-type crystalline silicon solar cells – is achieved through the high selectivity of the junctions used: a passivating electron-selective n+-type polysilicon on oxide (POLO) junction at the cell’s minus contact and a hole-selective p+-type POLO junction at the plus contact.
As ISFH announced, efficiencies of over 25% have so far only been reached using n-type silicon in combination with boron diffusions or heterojunctions made of amorphous silicon. The method used by ISFH of laser ablation for contact opening furthermore allows the industrial production of the record-breaking cell.
The project, which is running from July 2015 to June 2018, is being funded by the Federal Ministry for Economic Affairs and Energy (BMWi).