ABSTRACT
The optimization of organic solar cells in both space and energy–time domains have been preliminarily investigated, either experimentally or theoretically, in order to achieve high efficiency photoelectric energy conversion. Specifically, in the spatial domain, a “tertiary” block copolymer supramolecular nanostructure has been designed using a –DBAB- type of block copolymer, where D is a conjugated donor block, A is a conjugated acceptor block, and B is a nonconjugated and flexible bridge unit. Several –DBAB- type block copolymers 184have already been designed, synthesized, characterized, and preliminarily examined for target photovoltaic functions. In comparison to a simple donor–acceptor (D–A) blend film, a corresponding –DBAB- block copolymer film exhibited much better photoluminescence (PL) quenching and photoconductivity. These are mainly attributed to the improvement in the spatial domain for charge carrier generation and transportation. With respect to the energy levels and electron transfer dynamics of these materials, the photoinduced charge separation appears to be most efficient when the donor–acceptor frontier orbital energy offset approaches the sum of the charge separation reorganization energy and the exciton binding energy. Other donor–acceptor frontier orbital energy offsets have also been identified where the charge recombination becomes most severe, and where the ratio of the charge separation rate constant over the charge recombination rate constant becomes largest. Implications and ways of achieving these optimized energy levels are also briefly discussed.
