Slow Current Limits Organic Solar Efficiency

Scientists at Chemnitz University of Technology are developing cost-effective, printable organic solar cells, but slow electron movement causes transport resistance, reducing power output, and their latest research uncovers its root causes and potential solutions for improved performance.

Researchers at Chemnitz University of Technology, led by Prof. Dr. Carsten Deibel, are advancing the development of organic solar cells using novel semiconductors and established printing processes. These lightweight and cost-effective solar cells offer a promising alternative to traditional crystalline silicon modules. Their efficiency is hindered by slow charge transport, limiting overall power output.

Unlike conventional solar panels, organic solar cells are manufactured using a printable “ink,” creating a disordered light-absorbing layer. This disorder significantly slows the movement of electrons and holes, increasing transport resistance, a major factor reducing efficiency. Transport resistance leads to charge carriers getting in their own way, lowering the fill factor and overall power.

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To deepen their understanding of this issue, Deibel and Saladina conducted extensive studies on different organic solar cell designs. By analyzing current-voltage characteristics under illumination, they assessed how charge generation, recombination, and transport interact to impact power conversion efficiency. Their results were then compared with the suns-Voc method, which constructs an alternative current-voltage curve unaffected by transport resistance.

The findings indicate that despite transport resistance being a significant limiting factor, there are no fundamental barriers to achieving high-efficiency printed organic solar cells. Charge transport has improved over the years, but the exact link between fill factor losses and transport resistance remained unclear. A follow-up, researchers from various German universities, further explores the physical origins of transport resistance. They highlights that beyond recombination, the shape of the density of states in organic materials also plays a crucial role.