Non-steady state operation of polymer/TiO2 photovoltaic devices

Kirov KR, Burlakov VM, Xie ZB, Henry BM, Carey MJ, Grovenor CRM, Burn PL, Assender HE, Briggs GAD

We present data on the initial period of operation of Gilch-route NMH-PPV/TiO2 composite solar cells (CSCs) which show that during this period the CSCs operate in a non-steady state regime. The behavior is complex and may include a gradual rise of the open circuit voltage (V-oc) and of the short-circuit current density (J(sc)) with time, a passage through a maximum of either or both parameters, and even a sign reversal. The mechanisms most probably contributing to the transient processes are: i) diffusion driven redistribution of charges resulting in the build up of a quasi steady state charge density profile across the device; ii) photo-doping resulting in a relatively slow increase of the average charge carrier concentration and consequently of the conductivity of the device. The latter is responsible for a strong decrease in V-oc, and is evidenced by the significant increase in dark current after device illumination.

Keywords:

ORIGIN

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SOLAR-CELLS

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MEH-PPV/titanium dioxide solar cells

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time dependent performance

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photo-doping