Rigorous wave-optical treatment of photon recycling in thermodynamics of photovoltaics: Perovskite thin-film solar cells

The establishment of a rigorous theory on the thermodynamics of light management in photovoltaics that accommodates various loss mechanisms as well as wave-optical effects in the absorption and reemission of light is at stake in this contribution. To this end, we propose a theoretical framework to calculate the open-circuit voltage enhancement resulting from photon recycling (Delta V-oc(PR)) with rigorous wave-optical treatment. It can be applied to both planar thin-film and nanostructured single-junction solar cells. We derive an explicit expression for Delta V-oc(PR), which reveals its dependence on internal quantum luminescence efficiency, parasitic reabsorption, and photon escape probabilities of reemitted photons. While the internal quantum luminescence efficiency is an intrinsic material property, both latter quantities can be determined rigorously for an arbitrary solar cell architecture by three-dimensional electrodynamic dipole emission calculations. We demonstrate the strengths and validity of our framework by determining the impact of photon recycling on the V-oc, of a conventional planar organometal halide perovskite thin-film solar cell and compare it to established reference cases with perfect antireflection and Lambertian light scattering. Our calculations reveal Delta V-oc(PR) values of up to 80 mV for the considered device stack in the absence of angular restriction and up to 240 mV when the escape cone above the cell is restricted to theta(out) = 2.5 degrees around the cell normal. These improvements impose severe constraints on the parasitic absorption as a parasitic reabsorption probability of only 2% reduces the Delta V-oc(PR) to 100 mV for the same angular restriction. Our work here can be used to provide design guidelines.