Organic solar cells (OSCs) could be useful power sources, e.g., for portable and wearable devices. For OSCs based on glass substrates, power conversion efficiencies (PCEs) up to 19 % have been achieved. Flexible OSCs, which might be well-suited to wearable devices, have lower PCEs so far. This is due to the properties of the flexible, transparent electrodes such devices require. Networks of silver nanowires (AgNWs) could be useful transparent electrode materials. However, randomly stacked nanowires with loose contacts have an increased electric resistance.

Yaowen Li, Soochow University, Suzhou, China, and colleagues have developed a chemical “welding” process for AgNWs which facilitates contact between the nanowires and decreases resistance. The team used a reduction strategy to grow Ag in situ at the junctions between nanowires. They used the ionic liquid 3-(2,3-dihydroxylpropyl)-1-methyl-1H-imidazol-3-ium chloride as a reducing agent, silver nitrate (AgNO₃) as the silver source, and a polyethylene terephthalate (PET) substrate with embedded AgNWs.

The chloride in the ionic liquid regulates the Ag⁺ concentration via the formation of AgCl, and the Ag⁺ is slowly reduced to give metallic Ag. The reduced Ag “welds” the junction sites between the AgNWs and promotes good electrical contact in the nanowire network. Single-junction flexible OSCs based on the resulting chemically welded flexible, transparent electrode achieved record power conversion efficiencies of 17.52 %.

• Realizing 17.5% Efficiency Flexible Organic Solar Cells via Atomic-Level Chemical Welding of Silver Nanowire Electrodes,
  Guang Zeng, Weijie Chen, Xiaobin Chen, Yin Hu, Yang Chen, Ben Zhang, Haiyang Chen, Weiwei Sun, Yunxiu Shen, Yaowen Li, Feng Yan, Yongfang Li,
  J. Am. Chem. Soc. 2022.
  https://doi.org/10.1021/jacs.2c01503