Atomistic description of III-nitride light emitting diodes and perovskite solar cells

The use of atomistic approaches for device simulations has gained considerable attention in the last decades, due to the downscaling of device dimensions. During my PhD research activity, I focused on the theoretical characterization, at the atomic scale level, of III-nitride alloys and perovskite materials composing the active region of optoelectronic devices. In particular, I applied the tight binding model in order to describe the effect of compositional fluctuations on the performance of InxGa1−xN/GaN quantum-well based light emitting diodes. The main finding is that the non-uniform distribution of In atoms yields a substantial broadening of the emission spectrum and a red-shift of the peak emission energy. These results have been recently published in: Japanese Journal of Applied Physics “Characterization of non-uniform InGaN alloys: spatial localization of carriers and optical properties”, Physical Review Applied “Impact of compositional non-uniformity in (In, Ga)N based light emitting diodes” and Journal of Applied Physics "Simulating random alloy effects in III-nitride light emitting diodes". Furthermore, I used an ab-initio approach based on density functional theory in order to simulate the interaction between CH3NH3PbI3 perovskite and functionalized Ti3C2 MXene. I found that the work function of CH3NH3PbI3 is influenced by the interaction with MXene, due to the presence of surface dipoles at the interface between the two materials. Interestingly, the work function tuning has a non-linear dependence on the relative fraction of O, F and OH terminal groups of Ti3C2. This study resulted in two recent publications: Nature Materials “Titanium-carbide MXenes for work function and interface engineering in perovskite solar cells” and Advanced Functional Materials "Non-linear work function tuning of lead halide perovskites by MXenes with mixed terminations". Finally, I developed a novel theoretical framework to fit the tight binding Hamiltonian matrix elements, employing a particle swarm optimization algorithm and using the density functional theory band structure of the bulk system as fitting target. I demonstrated the suitability of the mentioned procedure referring to the CH3NH3PbI3 perovskite, in all its three crystal phases, as a benchmark for simulations. This study has been presented in International Conference on Numerical Simulation of Optoelectronic Devices (NUSOD) 2020 “Tight binding parameterization through particle swarm optimization algorithm”.