Abstract
Recently recorded efficiencies of Cu(In,Ga)Se2 based solar cells were mainly achieved by surface treatment of the absorber that modifies the buffer-absorber interface region. However, only little is known about the electronic properties within this region. In this manuscript voltage dependent admittance spectroscopy is applied to low temperature grown Cu(In,Ga)Se2 based solar cells to detect near interface defect states in the absorber. Under non-equilibrium conditions even defect states close to the interface may cross the Fermi level and hence are detectable using capacitance based measurement methods, in contrast to the case of zero bias conditions. Such defects are of potential importance for understanding device limitations and hence, adequate characterization is necessary. A SCAPS model is developed including a near interface deep acceptor state, which explains the frequency and voltage dependence of the capacitance. Using the same model, also the experimental apparent doping density is explained.
Highlights
Among the thin film technologies for photovoltaic applications, Cu(In,Ga)Se2 (CIGS) based solar cells reached highest efficiencies of 22.6%.1 The interface between the absorber and the buffer layer plays a crucial role in achieving high efficiencies
In this contribution we investigate the electronic properties of the near surface region of the CIGS absorber layer
Recent admittance and temperature dependent IV measurements on similar devices treated under various post-deposition treatment (PDT) conditions indicated the capacitance step to be due to a barrier.[28,29]
Summary
Among the thin film technologies for photovoltaic applications, Cu(In,Ga)Se2 (CIGS) based solar cells reached highest efficiencies of 22.6%.1 The interface between the absorber and the buffer layer plays a crucial role in achieving high efficiencies. Among the thin film technologies for photovoltaic applications, Cu(In,Ga)Se2 (CIGS) based solar cells reached highest efficiencies of 22.6%.1. Various methods were reported to optimize the electronic properties of the interface region such as an In finish after the 3-stage co-evaporation process,[2] partial electrolyte treatment,[3] KF post-deposition treatment (PDT)[4] and recently PDT with other alkalis.[1] apart from the n-type doping mechanism of Cd5–10 no investigations were carried out to measure deeper defect states close to the interface, which could considerably contribute to recombination, i.e. electrical active defect states. Based on the experimental findings a SCAPS12 model is developed, which incorporates the experimental insights to describe the electronic behavior of the investigated device
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