Low band gap rod-coil diblock copolymer as nanostructuring compatibilizer of PCPDTBT/CdSe nanocrystals-based hybrid solar cells

In recent years the use of nanocrystals (NCs) as inorganic semiconductors in conjugated polymer-based hybrid solar cells (HSCs) results as a challenging target for researchers because of their high electron mobility and good mechanical robustness compared to fullerene derivatives, as well as their capability of harvesting photons in the visible to near-infrared region of the solar spectrum. Unfortunately HSCs still suffer from a major drawback, that is a poor control over the organic donor and inorganic acceptor domain size distributions. The domain size of the donor and acceptor materials should be comparable to the exciton diffusion length in order to increase the probability of exciton dissociation, and to improve charge carrier transport and collection at the device electrodes. The readiness of inorganic NCs to macrophase separate from non-polar conjugated polymers at higher loading concentrations, prevents the building of a controllable interpenetrating percolation network. A suitable nanostructuring compatibilizer can induce selective intermolecular interactions, leading to morphological order associated to an improvement in the interface processes, which consequently drive a strong rising in the performances of the device by decreasing recombination losses. For this purpose, block copolymers are particularly significant because they can self-assemble through phase separation by rationally tailoring the blocks using functional moieties with different physical-chemical behaviours. We report on the synthesis of a rod-coil diblock copolymer based on poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b:3,4-b']dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT), a low band gap copolymer, and a coil block of poly(4-vinylpyridine) able to interact with semiconducting CdSe NCs with the aim of using it as coordinating material in the preparation of PCPDTBT/CdSe NCs-based hybrid solar cells.