High-Throughput Screening of Materials for Rainbow Multi-Junction Organic Solar Cells

Single-junction organic solar cells (OSC) nowadays have reached promising power conversion efficiencies around 19%. Besides new materials, going beyond the current efficiencies could, in principle, be achieved by multi-junction devices, which promise a reduction in thermalization losses [1]. For this promise to become a reality, two items should be addressed, namely, the multi-junction geometry and the screening of materials with very different gaps.<br/>In this talk, we will present a multi-junction in-plane spectral splitting geometry that we call Rainbow solar cells [2]. In this geometry, a series of sub-cells are placed next to each other laterally, and illuminated through an optical component that splits the incoming white beam into its spectral components, thus matching local spectrum and absorption for each sub-cell. The fabricated n-terminal devices are capable of extracting the maximum power of each sub-cell without the need for current matching nor processing challenges. We demonstrate the concept for PM6:IO-4Cl and PTB7-Th:COTIC-4F blends, as high and low band-gap sub-cells, respectively. In agreement with simulations, we show an efficiency increase of around 30% of the Rainbow geometry with respect to our best single junction device [2]. Finally, we use high throughput methods based on gradients on the parameters of interest [3] to screen tens of materials exhibiting either wide band gap or narrow bandgap, and thus pushing the efficiency of the Rainbow multi-junction further up.<br/>[1] I. M. Peters et al, <i>Prog. Photovolt</i>. 31 (2023) 1006.<br/>[2] M. Gibert-Rocat et al, <i>Adv. Mater</i>, (2023) https://doi.org/10.1002/adma.202212226<br/>[3] X. Rodríguez-Martínez et al, <i>Ener. Environ. Scien</i>. 14 (2021) 986.