For the first time, the research group at the Photovoltaic Materials Unit of the National Institute for Materials Science (NIMS — Sukesatsu Ushioda, president), led by Dr. Liyuan Han, achieved an energy conversion efficiency rate of fifteen percent in perovskite solar cells, as officially recognized certified at an international test center.
The most conversion efficiencies in such solar cells thus far reported had been measured with small-sized cells — about 0.016 in². A conversion efficiency of 20.1 percent had previously been reported, but the size of the cells used in that study — 0.0145 in² — resulted in a large measurement error, and the report did not present the measurement method. To advance research and development of perovskite solar cells steadily, and base it on reliable data, one must measure the conversion efficiencies at an international public test center.
The research group increased conversion efficiency and reproduction of perovskite solar cells by inventing a new method for controlling the morphology of the perovskite layer. Additionally, since the conventional material used for charge carrier transport layers is hydrophilic, the cell’s conversion efficiency drops rapidly.
Here, we developed a new material which is hydrophobic and very carrier-mobile, with which we successfully improved the stability of perovskite solar cells. Based on these results, we expanded to solar cell to over 1 cm² (0.155 in²) and improved the method for created the device. That is how we achieved our 15 percent conversion efficiency. Based on these outcomes, we aim to improve conversion efficiency even further by developing materials with even higher performance and controlling performance in perovskite solar cells.
This research was conducted partly in conjunction with the JST (Japan Science & Technology Agency) – sponsored project “Device physics of dye-sensitized solar cells” supervised by Masafumi Yamaguchi, Principal Professor at Toyota Technological Institute, under the research area “Creative research for clean energy generation using solar energy” in the Core Research of Evolutional Science & Technology (CREST) program. This study was presented at the International Conference on Hybrid & Organic Photovoltaics held in Rome from May 10 thru 13, 2015.
