Modeling minority carrier transport and μτ determination in cadmium selenide thin film solar cells

A simple model for the transport of minority holes in Cadmium Selenide (CdSe) solar cells is presented. Further, via a fitting scheme, the model is shown to permit the subsequent determination of the minority carrier mobility-lifetime (μτ) product in CdSe solar cells. The mobility-lifetime (μτ) product is an essential characterization parameter in solar cells, and semiconductors in general. For materials such as CdSe, whose diffusion lengths are insufficient to efficiently collect photogenerated carriers, devices must rely on the presence of an internal electric field to aid in collection – in these devices, transport is noted to be “range dominated”. As the μτ-product is effectively a metric by which scientists describe the response of the material to a given electric field, its determination, particularly within range-dominated solar cells, is paramount to the greater characterization of the device. Via our fitting scheme, we find our CdSe devices to be characterized by minority-hole μτ values on the order of ≈5∙〖10〗^(-10) [〖cm〗^2/V], at times approaching values of ≈1∙〖10〗^(-9) [〖cm〗^2/V] – depending upon device structure and the trap density of states in the material. The transport model is shown to be applicable to both PIN and NIP CdSe device structures. The model goodness-of-fit, in terms of standard deviation, is shown to be in agreement with experimental values, with model values deviating less than 5% from experimental values for the majority of devices measured