Optimum energy levels and offsets for organic donor/acceptor binary photovoltaic materials and solar cells

摘要

Optimum frontier orbital energy levels and offsets of an organic donor/acceptor binary type photovoltaic material have been analyze using classic Marcus electron transfer theory in order to achieve the most efficient photo induced charge separation. This study reveals that an exciton quenching parameter (EQP) yields one optimum donor/acceptor frontier orbital energy offset that equals the sum of the exciton binding energy and the charge separation reorganization energy, where the photo generated excitons are converted into charges most efficiently. A recomination quenching parameter (RQP) yields a second optimum donor/acceptor energy offset where the ratio of charge separation rate constant over charge recombination rate constant becomes largest. It is desirable that the maximum RQP is coincidence or close to the maximum EQP- A third energy offset is also identified where charge recombination becomes most severe. It is desirable that the most seven charge recombination offset is far away from maximum EQP offset. These findings are very critical for evaluating and fine tuning frontier orbital energy levels of a donor/acceptor pair in order to realize high efficiency organic photovoltaic materials.