Photovoltaic and light emitting devices based on perovskites have shown an impressive development in the last years. Despite the fast progress, many studies relied still on a trial and error approach in order to further boost device efficiencies. The aim of the thesis is therefore to get further inside into phenomena related to the fundamental photophysics on both perovskite solar cells and LEDs. The work has been structured in three parts: Perovskite‐Perovskite Homojunctions via Compositional Doping. One of the most important properties of semiconductors is the possibility to control their electronic properties via intentional doping. Nevertheless doping in perovskite remains nearly unexplored and perovskite pn‐junctions have never been reporter. In this work we aim to intentionally dope the material to build a perovskite homojunction. Efficient photo‐ and electroluminescence by trap states passivation in vacuum‐deposited hybrid perovskite thin films. Trap states account for most of the efficiency losses in perovskite LEDs. The goal is therefore to passivate Trap states in MAPI perovskite LEDs using high excess of MAI. The so produced films should increase the overall efficiency. Influence of hole transport material ionization energy on performance of perovskite solar cells. The Voc is among the most important parameters controlling the power conversion efficiencies in solar cells. We thus investigate if the Voc is either influenced solely by the nature of recombination or additionally by the ionization potential of the organic transport materials.