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The quantum efficiency (QE) of a solar cell is subject to important changes with applied forward bias, which are not solely depending on effective variation of the internal quantum efficiency (IQE). QEs measured with applied bias voltage are affected by the magnitude of parasitic resistance�s, and in multi-junction/multi-layer solar cells by the presence and interaction of different space-charge regions. QE measured in bias conditions in general differs from the primary photocurrent; therefore it will be referred to as apparent quantum efficiency (AQE). We examine the AQEs of CdTe devices in comparison to standard cells. AQE well above unity, i.e. up to 100 at high forward bias, have been measured. Positive and negative AQE are measured in different wavelength regions. Back contact influence and defect related features, such as sub bandgap generation, are observed. Measurements show how the front region of the device plays a fundamental role in the photovoltaic characteristics and leads one to hypothesis for these cells a sensitisation of the front layers and/or a hook band structure.

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Authors: AGOSTINELLI G, JRC, IES, Renewable Energies Unit, Ispra (IT);DUNLOP E D, JRC, IES, Renewable Energies Unit, Ispra (IT);BATZNER D, Thin Films Physics Group, Laboratory for Solid State Physics, Zurich (CH)
Bibliographic Reference: An oral report given at: The 17th European Photovoltaic Solar Energy Conference and Exhibition. Held in: Munich (DE), 22-26 October 2001
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