Single-Material Organic Solar Cells Based on Small Molecule Homojunctions: An Outdated Concept or a New Challenge for the Chemistry and Physics of Organic Photovoltaics?

Single-material organic solar cells (SMOSCs) are on the forefront of research on organic photovoltaics (OPV). The generic term of SMOSCs encompasses a large variety of chemical structures implying very different basic concepts. Polydisperse << double cable >> polymers and oligomers with acceptor groups linked to the conjugated backbone by a flexible spacer and donor-acceptor block copolymers are at present, the most investigated and efficient systems with spectacular progress in conversion efficiency achieved in the past 2-3 years. However, besides this mainstream SMOSCs research, a few recent publications describe OPV cells constituted of homojunctions based on small pi-conjugated molecules. While the process of charge generation in such systems is still a matter of debate due in particular to the possible direct photogeneration of charge-carriers, devices with significant performance have been recently reported. After a brief overview of the most recent advances on the various types of SMOSCs, recent remarkable results on homojunction OPV cells based on small pi-conjugated molecules are discussed in order to highlight the potential fundamental and technological interest of this emerging field of research.