Charge Transfer at Semiconductor Heterojunctions

After splitting of the exciton at the heterojunction and further separation of the charge-transfer state, the charges (or polarons) need to be transported within the semiconductor materials network to the respective electrodes. Despite the recognition that it is mainly the separation of the charge-transfer states that limits current polymer polymer solar-cell devices, charge transport also has to be considered, because it is another potential loss mechanism. We will briefly cover this topic the interested reader is referred to a recent review by Blom et al. [7]. 

An alternative model to account for low mobilities in organic semiconductors is the multitrapping and release model. Traps are locahzed levels as lattice defects or impurities in which charge carriers are immobilized. The ones localized near the center of the bandgap are called deep traps, while the ones close to the conduction or valence band 

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