Finnish researchers increase efficiency of black solar cells

Researchers at the Finnish Aalto University have managed to increase the efficiency of black solar cells to 22.1 percent. The university thus improves its own efficiency record by almost four percentage points.

The high conversion rate of 22.1 percent could be achieved with black silicon solar cells with a nanostructure, together with a special alumina film that ensures that the solar cell performs better. Also, the metal contacts were integrated into the back of the cell. The film made it possible to reduce surface recombination, the bottleneck of black silicon. In surface recombination, an electron removed from its bond by a photon immediately falls back from the p-layer to its original position, causing the energy that the electron was given to disappear again. In order to generate energy, the electron must recombine via another part of the photovoltaic cell, namely from the p-layer to the n-layer via a conductive connection with a resistor.

Black solar cells are useful in northern areas because the black cells are better able to capture solar radiation from all angles. The sun shines from a low angle in these areas for much of the year, the researchers said.

The aim is to apply the technology to other cell structures, including thin, multi-crystalline solar cells. The cells in this study were fabricated with relatively impure p-silicon. The researchers think they can achieve even higher yields with purer n-silicon. The maximum size of the cells now produced was 9 square centimeters. The hope is to be able to quickly scale up the wafers to industrial level.

The development of these cells continues in the European Union’s Black project, where photovoltaic technology is further developed together with industry. The results of the research are published in the journal Nature Nanotechnology.

p-layer and n-layer, source

Update Wednesday 20 May, 17.08: following a comment from ikwilwp8 part about recombination edited