|
Optimizations of organic/polymeric optoelectronic materials and devices in both space and energy/time domains have been studied, both experimentally and theoretically, in order to achieve high efficiency photoelectric conversion. Specifically, at spatial domain, a 'tertiary' block copolymer supra-molecular nano structure has been designed, and a series of -DBAB- type of block copolymers, where D is a conjugated donor block, A is a conjugated acceptor block, and B is a non-conjugated and flexible bridge unit, have been synthesized, characterized, and preliminarily examined for photoelectric conversions. In comparison to simple donor/acceptor (D/A) blends, -DBAB- block copolymers exhibited much better photoluminescence quenching and photoconductivity. These are mainly attributed to improvement in spatial domain for charge carrier generation and transportation in -DBAB- block copolymers then in simple D/A blends. In materials energy levels and electron transfer dynamic regime, theoretical analysis revealed that, the photo (or thermal) excitation induced charge separation appears to be most efficient when the corresponding donor/acceptor frontier orbital level offset is equal to the sum of the charge separation reorganization energy and the exciton binding energy. Other donor/acceptor frontier orbital energy offsets were also identified where the charge recombination becomes most severe, and where the charge separation rate constant over charge recombination rate constant become largest. This dynamically favored charge separation mechanism is also proposed to explain the general 'doping' induced charge carrier generation. Implications of these findings and future approaches are also discussed in order to achieve inexpensive, lightweight, flexible, and high efficiency 'plastic' solar cells or photo detectors.
|
