Regensburg 2013 – scientific programme

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DS: Fachverband Dünne Schichten

DS 17: Focus Session: Thin Film Photovoltaic Materials and Solar Cells I

DS 17.5: Topical Talk

Wednesday, March 13, 2013, 11:45–12:15, H32

Energy Band Alignment in Thin Film Solar Cells — •Andreas Klein — Technische Universität Darmstadt, Institut für Materialwissenschaft

The energy band alignment at interfaces between covalently bonded semiconductors like Si and GaAs can be well described using the charge neutrality level concept. The electrostatic potential distribution across an interface of such materials can be directly obtained once the band alignment and the doping profiles are known. In contrast to such ideal semiconductor interfaces, thin film solar cells employ more ionic compounds, combination of dissimilar materials, and (low temperature) film deposition techniques being far from equilibrium. As a consequence, deposited films may contain a high concentration of defects, which can prevent a variation of the Fermi energy. Such a bulk Fermi level pinning limits the evolution of band bending at an interface and can even lead to a large variation of energy band alignment. These effects may be a natural explanation for the sensitivity of solar cell efficiency on the selection of material combinations and deposition techniques and therefore enable new optimization strategies. It further suggests that simulation of electrical cell characteristics assuming ideal semiconductor behaviour may not be adequate.