Synthesis, optical properties and photovoltaic applications of hybrid rod–coil diblock copolymers with coordinatively attached CdSe nanocrystals

Abstract

The performance of hybrid solar cells based on conjugated polymers and nanostructured inorganic semiconductors is often limited by the poor interfacial interaction and the lack of controlled phase separation. Improvements are being made by building intimate contact between the two components through coordinative linkages. In this contribution, three rod–coil diblock copolymers (DCPs) of the modified poly(3-hexylthiophene)-polystyrene (P3HT-PS) type with different phosphorus-containing functional groups for binding to inorganic nanoparticles are reported. Their corresponding P3HT-PS-CdSe hybrid DCPs (HDCPs) were prepared by ligand-exchange with chemically prepared CdSe nanocrystals. The three DCPs have different size disparity between the rod and coil blocks, where the dominant block dictates their solid state aggregation behavior. As a result, the three DCPs show very different fluorescence properties in the solid state. After binding with CdSe nanocrystals, nanocrystal association appears to dominate the solid state aggregation in all three HDCPs, making them exhibit comparable solid state optical properties. Solar cell devices of HDCPs showed high open circuit voltages of 1.13–1.40 V and improved power conversion efficiencies (PCEs) over devices fabricated from the corresponding DCPs without CdSe attachment. It is believed that the improvement of the PCE is brought about by intimate contact between the P3HT and the CdSe components, which enhances the initial charge separation from P3HT to the CdSe nanocrystals. The device performance is however hampered by the low nanoparticle loading and the short P3HT block length, which are being addressed.