Researchers in China have improved the performance and durability of inverted perovskite solar cells by creating two new 56pi electron fullerene derivatives, known as C60-TFB and C60-TFP, for use as electron transport layers.
The research team synthesized C60-TFB and C60-TFP via a 1,4-asymmetric addition approach, giving the molecules bulky tert-butyl, indole and azaindole groups. These groups prevent dimerization when exposed to light and provide a strong bond with the perovskite layer, resulting in fewer defects. The resulting electron transport layer forms an effective barrier to stop the migration of iodide ions from the perovskite layer and silver atoms from the electrode.
Devices tested with the new C60-TFP electron transport layer achieved an energy conversion efficiency of 25.93 percent, higher than the 24.08 percent achieved with conventional PCBM-based devices. During a period of 1,000 hours of continuous illumination at 55 degrees Celsius, the new devices retained 81.9 percent of their original efficiency. By comparison, devices using PCBM had only 62.9 percent. The results confirm the advantages of the new fullerene derivatives for increasing stability in perovskite solar cells.
Professor Shangfeng Yang commented: “Coinciding with the 40th anniversary of the discovery of fullerene, he is confident that more new fullerene-based electron transport materials for high-performance perovskite solar cells will emerge in the future.”
