Feb 6 (Renewables Now) - The US National Renewable Energy Laboratory (NREL) has found that surface recombination in single-crystal and polycrystalline films is an obstacle in the quest for improved performance of perovskite solar cells.
Scientists at the lab have determined that recombination in other parts of a methylammonium perovskite film is not as important as that on the surface, both the top and bottom of the cell.
"There are multiple sources of possible recombination. In order to improve your device, you're asked to get rid of all non-radiative recombination. Typically people forget about surfaces. They think about grain boundaries. They think about bulk defects and so forth," said Matthew Beard, lead author of the research paper.
The findings, published in Nature Energy, include one key discovery -- surface recombination is “worse” for single crystalline samples than for polycrystalline samples. Chemically, excess methylammonium iodide was present on the surface of the polycrystalline film but absent on the single-crystal sample, the NREL scientists explain.
The research suggests that a light coating of a protective material on the surface of the polycrystalline thin films could further boost the performance of perovskite solar cells.