The Shockley-Queiser efficiency limit of conventional photovoltaic absorbers can in principle be overcome in so-called intermediate band semiconductors. Due to the existence of one partially filled intermediate bands (IB), these materials can soak two subsequent photons with energies in the range of two sub-band gaps and deliver a high energy electron to the external circuit. Conceptually, IB absorber materials can be obtained by doping appropriate semiconductors. In this context, chalcogenides, such as In2S3, ZnIn2S4, MgIn2S4 and MnIn2S4, show a lot of promise, because they meet the optimal band gap criterion quite closely, there are well known techniques for preparing them as thin films and the incorporation of transition metals leads to d-orbital splitting in an octahedral field. Thermodynamically stable dopants that induce intermediate bands in these host semiconductores are, however, not identified yet.

Thus, the goal of this proposal is to characterize the electronic and thermodynamic properties of variousdopants by means of electronic structure calculations. We will focus on transition metals (TM), namely, Cr, Ti, V and Nb, in the crystalline matrix of In2S3, ZnIn2S4, MgIn2S4 and MnIn2S4. The goal is to identify the position of the induced impurity band with respect to the host bands, to understand the interaction of the incorporated TMs with the native defects, and to predict the thermodynamic stability of the parent semiconductors in the presence of the TMs. Moreover, the influence of the formed IBs on phonon-assisted photon absorption will be studied.

AZ: GH 209/1-1

Project Period: April 2020 – Aug. 2025