Using Transient Measurements to Study the Operation of Polymer Solar Cells
Dr Chris McNeill
Department of Materials Engineering, Monash University, Australia
3:30 pm Friday, 17 June 2011, EN101 Lecture Theatre (EN Building), Hawthorn.
Polymer solar cells have attracted considerable attention due to their potential as a low-cost photovoltaic technology. The operation of polymer solar cells differs significantly from that of conventional silicon solar cells. In particular photo-excitation of organic semiconductors does not lead directly to the production of free charge carriers but rather produces tightly bound excitons. This requires the use of a donor-acceptor heterojunction where two materials are combined with different electron affinities to drive exciton dissociation. Following exciton dissociation charges must also be separated from the donor-acceptor interface and transported to their respective electrodes. Due to the low exciton diffusion length (~ 10 nm) the so-called bulk heterojunction architecture consisting of a blend of donor and acceptor with nanoscale, interconnected phases is used in the most efficient polymer cells. This disordered blend architecture, however, can further complicate charge generation and collection processes. In this talk I will focus on the use of transient photocurrent and photovoltage techniques to probe the operation of polymer solar cells. Transient photocurrent measurements allow for the dynamics of charge collection to be studied, while transient photovoltage measurements allow for the dynamics of charge recombination to the investigated. The operation of polymer solar cells using a range of different electron acceptors will be discussed, and the influence of charge trapping on device performance highlighted.
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