Solar energy conversion to electrical energy by organic solar cells (OSCs) is an emerging technology, which has been significantly advanced due to its tunable optoelectronic properties. These technologies can be solutionized and can be fabricated using commercially available cost-effective coating techniques, which represents a substantial advantage in reducing manufacturing costs for fabrication, layout, and recycling. Applications of this technology are being explored for large-area modules, including buildings, facades, agricultural, and space applications. This emerging photovoltaic technology minimizes the levelized cost of electricity and energy payback time compared to silicon photovoltaic technology. So far, the efficiency of single-junction OSCs for single-junction organic solar cells (OSCs) has reached more than ~20,2% (compared to the theoretical value of ~33%). The exploration of novel absorbers and charge transport materials, novel device designs, fabrication techniques are particularly relevant to improve efficiency and stability, as well as commercial viability. In this quest, understanding structure-stability-property relationships is equally important.
A collaborative research between the NMR (UCCS, Univ Lille) and RPE (LASIRE, Univ Lille) groups and the Center for Organic Polymers and Solids (CPOS, UC Santa Barbara) investigated the impact of different Al and Ag electrodes on the interfacial morphology and stability of photoactive layers in organic solar cells. OSCs with an aluminum (Al) top electrode exhibit lower stability compared to silver (Ag) electrode devices upon thermal annealing, where thermal stress induces the diffusion of Al and Ag atoms toward the photoabsorber layer. The diffused Al atoms cause surface recombination at the interface between the photoactive layer and an interlayer. Specifically, X-ray photoelectron spectroscopy suggests the different local chemical environments of PM6 and Y6 moieties in PM6:Y6/Al contact devices. These results are corroborated by solid-state NMR (28,2 T, 1H = 1200 MHz) and EPR measurements, indicating the formation of ionic and organometallic species in the photoactive sublayers, which are estimated to be less than 5 wt%. In comparison, Ag atoms do not negatively affect the morphology of the photoactive layers and the associated device physics. The study of the electrode-reactive photoactive layer interfaces by multiscale characterization techniques and device physics is expected to provide guidance for future interfacial engineering strategies aimed at developing stable and efficient organic solar cells.
Link to publication: https://onlinelibrary.wiley.com/doi/10.1002/adfm.202308618
Link to the cover: https://onlinelibrary.wiley.com/doi/10.1002/adfm.20247029