A new paradigm for thin-film solar cells: the case of Earth abundant Cu-N ternary compounds

The design of thin film solar cells is extremely sensitive to the choice of the material forming the absorbing layer. Indeed, many of the limitations of solar cell devices are either directly linked to the intrinsic properties of the absorber such as in CdTe or design-related indirect consequences of this choice such as for SnS-based devices. Most of the design of current thin film solar cells rely on chalcogenide materials as the absorbing layer. We propose a new paradigm based on Earth abundant Cu-N ternary compounds as the absorbing layer. We will present the theoretical and experimental investigation of the electronic properties of two Cu-N compounds with interesting photovoltaic properties namely CuSrN and CuTaN$_{2}$. We performed state-of-the-art defect calculation and GW-based band structure calculations. CuTaN$_{2}$ was synthesized by ion exchange and its absorption onset was subsequently characterized with diffusive reflectance. While CuSrN displays interesting p-doped capability and defect immunity similar to Cu(In,Ga)Se$_{2}$, CuTaN$_{2}$ presents very strong absorption with a sharp absorption onset in the optimal range for photovoltaic conversion. Finally, we will address potential pitfalls of such absorbers related to stability with respect to O$_{2}$ and H$_{2}$O.