Theory-Based Insights into Interfacial Effects Influencing the Performance and Stability of Thin-Film Photovoltaics

The transformation and utilization of solar energy with photovoltaics is becoming an increasingly cost-effective renewable energy source to supplant fossil-based alternatives. Rapid and parallel advances in storage solutions like batteries or in chemical bonds via (photo)electrochemical (PEC) processes are further accelerating this transformation. Underpinning all of these technologies are the creation and optimization of complex interfaces required for the desired separation and transfer of charge carriers, chemical reactivity, and stability. First-principles based calculations offer one avenue for providing insight into many of the fundamental details of these heterointerfaces that can so strongly influence device performance. Here we detail many examples of particular relevance to thin-film photovoltaics, such as the choices for particular absorber compositions and heterojunction partners of other layers like buffer layers and transparent contacts, and common deposition and post-processing treatments. Using hybrid density functional theory calculations, we will discuss how these choices, as well as the role of alloying in different layers, can steer important device variables such as band gap, band offsets, doping and stability. These properties are often interrelated and can complicate device optimization. We will primarily illustrate how understanding these effects have led to gradual improvements in conventional thin-film photovoltaics (e.g. those based on Cu(In,Ga)(S,Se)₂ and CdTe), but will discuss how they are also relevant to alternative absorbers like wider-bandgap chalcopyrites and the hybrid perovskites.<br/>This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and partially supported by the Department of Energy office of Energy Efficiency & Renewable Energy (EERE) and by the HydroGEN Advanced Water Splitting Materials Consortium, established as part of the Energy Materials Network under the EERE Hydrogen and Fuel Cell Technologies Office.