Organic photovoltaic donor materials developed so far can be categorized into two main classes: conjugated polymers and small molecular compounds. Conjugated polymers have a one-dimensional -extended conjugated backbone, which is favor for transportation of photo-generated excitons and charge carriers. Besides, they generally have good film-formation potential. However, since they always have issues of batch-dependent average molecular weight and polydispersity, polymeric photovoltaic materials often suffer from poor batch reproducibility. On the other hand, small molecular compounds does not have batch-dependent problem since they have definite chemical structure and can be purified by a variety of methods. However, for the purpose of promising light absorption and good charge transportation among molecules, this kind of materials usually has a large and rigid -conjugated core. As a result, small molecular photovoltaic compounds tend to aggregate or crystallize in film state and are hard to form a well-qualified homogenous film, particularly in a large size.
Recently, we proposed a new type of organic photovoltaic materials, which is a kind of poly(rod-coil) polymers composed of alternatively definite conjugated and non-conjugated segments (Fig. 1a). The conjugated segments are opto-electronically active and suggested to be made from donor-acceptor (D-A) conjugated structure for a good solar light acquisition. In this presentation, we report the first five examples based on polyurethane chemistry (Fig. 1b) and highlight their property improvements over the small molecular reference compound due to good film formation. Furthermore, the polymer molecular weight has been found to have less influence on their photovoltaic performance.