Polarization anisotropy of charge transfer absorption and emission of aligned polymer: fullerene blend films

被引:29
作者
Vandewal, Koen [1 ]
Tvingstedt, Kristofer [1 ]
Inganas, Olle [1 ]
机构
[1] Linkoping Univ, IFM, SE-58183 Linkoping, Sweden
基金
瑞典研究理事会;
关键词
OPEN-CIRCUIT VOLTAGE; HETEROJUNCTION SOLAR-CELLS; TRANSFER EXCITONS; TRANSFER STATE; ELECTRONIC-STRUCTURES; RECOMBINATION; ENERGY; EFFICIENCY; ELECTROLUMINESCENCE; DISSOCIATION;
D O I
10.1103/PhysRevB.86.035212
中图分类号
T [工业技术];
学科分类号
08 ;
摘要
An improved understanding of the electronic structure of interfacial charge transfer (CT) states is of importance due to their crucial role in charge carrier generation and recombination in organic donor-acceptor (DA) solar cells. DA combinations with a small difference between the energy of the CT state (E-CT) and energy of the donor exciton (E-D*) are of special interest since energy losses due to electron transfer are minimized, resulting in an optimized open-circuit voltage. In that case, the CT state can be considered as a resonance mixture, containing character of a fully ionic state (D+ A(-)) and of the local polymer excited state (D* A). We show that the D* A contribution to the overall CT state wave function can be determined by measurements of the polarization anisotropy of CT absorption and emission of polymer: fullerene blends with aligned polymer chains. We study two donor polymers, P3HT and TQ1, blended with fullerene acceptors with different ionization potentials, allowing variation of the E-D* -E-CT difference. We find that, upon decreasing E-D* -E-CT, the local excitonic D* A character of the CT state increases, resulting in a decreased fraction of charge transferred and an increased transition dipole moment. For typical polymer: fullerene systems, this effect is expected to become detrimental for device performance if E-D* - E-CT < 0.1 eV. This however, depends on the electronic coupling between D* A and D+ A(-), which we experimentally estimate to be similar to 6 meV for the TQ1: PCBM system.
引用
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页数:9
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