Charge separation and recombination in self-organizing nanostructured donor-acceptor block copolymer films

A series of donor-acceptor diblock copolymers with varying molecular weight are studied in thin film and compared with an 'equivalent' blend formed from donor and acceptor homopolymers. Steady-state and transient spectroscopies are used to demonstrate a correlation between low molecular weight block copolymers and increased photoluminescence quenching (up to 99%) leading to higher yields of long-lived free charges. Such block copolymers are shown, by electron microscopy, to exhibit phase-segregated micrdomains whose size and periodicity are determined by their molecular weight. Photovoltaic devices made using these materials show a peak efficiency of 0.11% and correlate with our spectroscopic results, subject to a trade-off between charge generation and tranpsort/collection.