Publication date: 22nd July 2026
Single-junction organic photovoltaics (OPVs) nowadays have reached promising power conversion efficiencies, around 20%. Besides new materials, going beyond the current efficiencies could, in principle, be achieved by multi-junction devices, which promise a reduction in thermalization and absorption losses [1]. In this talk, we will present a multi-junction in-plane spectral splitting geometry that we call Rainbow solar cells and that aims at overcoming the limitations of stacked solution processed devices [2]. In the Rainbow 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 a high and low band-gap sub-cells, obtaining an efficiency increase of around 30% of the Rainbow geometry with respect to our best single junction device [2]. Then, we show that ternary mixing can further enhance the overall efficiency in this type of device by providing means to tune the Voc in narrow gap cells [3]. Monolithically integrated lateral cells have been fabricated using meniscus guided blade coating, and the corresponding PCE improves from 12.9% in single-junction devices to 15.9% in 2-junction devices (16.4% in simulations) and 17.3% in 3-junction devices (17.7% in simulations). Detailed balance analysis indicates that the potential of this geometry can be very high provided that high efficiency wide bandgap (2–2.5 eV) materials become available [3]. Finally, we use simulations based on real EQE and JV values to evaluate the potential of this technology for organic, silicon and perovskite solar cells and their combinations.
