Abstract: We present a straightforward and computationally cheap method to obtain the phonon-assisted photocurrent in large-scale devices from first-principles transport calculations. The photocurrent is calculated using nonequilibrium Green's functions with light-matter interaction from the first-order Born approximation while electron-phonon coupling (EPC) is included through special thermal displacements (STD). We apply the method to a silicon solar cell device and demonstrate the impact of including EPC in order to properly describe the current due to the indirect band-to-band transitions. The first-principles results are successfully compared to experimental measurements of the temperature and light intensity dependence of the open-circuit voltage of a silicon PhotoVoltaic (PV) module . We use the method to predict the solar cell efficiency of new Janus type 2D devices  and show that they outperform the silicon PV module. This work represents a recipe for computational characterization of future PV devices including the combined effects of light-matter interaction, phonon-assisted tunneling and the device potential at finite bias from the level of first-principles simulations.
 M. Palsgaard, T. Markussen, T. Gunst, M. Brandbyge, and K. Stokbro, "Efficient First-Principles Calculation of Phonon-Assisted Photocurrent in Large-Scale Solar-Cell Devices", Phys. Rev. App. 10, 014026 (2018)
 M. Palsgaard, T. Gunst, T. Markussen, K. S. Thygesen, and M. Brandbyge, "Stacked Janus Device Concepts: Abrupt pn-Junctions and Cross-Plane Channels", Nano Lett. 18, 7275 (2018)
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