The focus is on emerging photovoltaic (PV) technologies, based on devices with photo-active layers consisting of organic small molecules and/or polymers and quantum dots. Our aim is to gain a detailed understanding of how the energetic landscape in these active layers affects the fundamental processes of charge generation and recombination. We address specifically the processes limiting the power conversion efficiency (PCE) by following an approach that takes advantage of unique capabilities within our Center and benefits from the complementary expertise of the Center's faculty, including: the design and synthesis of novel materials, computational modeling, steady-state and advanced ultrafast spectroscopy and imaging, in-depth studies of thin film growth and microstructure formation during material processing, advanced charge transport analyses, and device engineering and optimizations.
Increasing Spectral Absorption and Power Conversion Efficiency of Organic Solar Cells with New Non-Fullerene Acceptors
State-of-the-art single junction organic bulk heterojunction solar cells that use fullerene derivatives as acceptors have now reached power conversion efficiencies beyond 11%. However, a major limitation in terms of further increasing the external quantum efficiency (EQE) of organic PV devices based on such acceptors is the incomplete spectral absorption of the active layers linked to the modest absorption coefficients of fullerenes in the visible spectrum. In this respect, developing alternative, that is, non-fullerene acceptors with large optical absorption strength and high electron mobility (at least equal but preferentially superior to that of fullerenes) is the way forward to enhance the power conversion efficiency of organic PV devices beyond the limits currently set by fullerene acceptors. New sets of molecular and polymer acceptors developed within this project will provide a test bed to establish meaningful structure-property relations, by studying the interfacial and bulk energetics, and donor acceptor interactions by computational approaches, acceptor-ETL interactions by photoelectron spectroscopy, and charge-separation dynamics by ultrafast spectroscopy and imaging techniques. The ultimate aim of this project is to develop systems that yield > 15% PCE by achieving near 100% IQE and EQE across a wide spectral range, an open-circuit voltage preferably above 1 V, and a high fill factor of > 70%.