Stacked organic solar cell increased to 15.9% efficiency

As research in solar technologies continues to advance, organic photovoltaics show increasing promise for their flexibility, environmental friendliness and lack of toxicity, but are often limited by their relatively low power conversion efficiency.

Looking for ways to increase this efficiency, Huang et al. developed a tandem organic photovoltaic cell by stacking a ternary near-infrared sub-cell on top of a visible-absorbing binary sub-cell that is nearest the substrate. In doing so, the authors were able to double the voltage of that of a single junction cell while maintaining a high current.

“The current is still high since cells can be tuned to capture more of the solar spectrum. This results in reduced electrical and optical losses, making tandem and other multijunction solar cells potentially far more efficient than conventional single-junction cells,” said author Stephen Forrest.

The wide and narrow energy sub-cells were combined into a multijunction device with an interconnecting layer in the charge combination zone. The almost lossless optical and electrical charge recombination zone was treated with isopropanol to connect the two sub-cell surfaces. The combined device also provided extra protection to the bottom cell.

This method of stacking was enabled by a non-fullerene acceptor which increased absorption of solar radiation. The overall power conversion efficiency was recorded as 15.9%.

“We believe that with the constant improvement and introduction of materials and fabrication processes, multijunction organic photovoltaics will soon have one of the highest efficiencies among thin-film solar cells,” said Forrest.

Source: “15.9 % organic tandem solar cell with extended near-infrared Absorption,” by Xinjing Huang, Bangjin Sun, Yongxi Li, Chao Jiang, Dejiu Fan, Jian Fan, and Stephen R. Forrest, Applied Physics Letters (2020). The article can be accessed at https://doi.org/10.1063/5.0005172 .