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Abstract

The aim of this thesis is to achieve a better understanding of the energetic alignment in organic multi-layered devices. The first part of this thesis is dedicated to the investigation of a new class of non-fullerene acceptor materials, N-Heteroacenes, in organic solar cells. Intentionally varying the side chain structure enables a threefold increase in device performance, partly due to an improved active layer morphology. In addition, by employing transient absorption spectroscopy, an uncommon electric field-dependent charge separation is found, starkly different than for the case of conventional fullerene acceptors. In the second part of this thesis, a novel method for the investigation of energy level alignment in organic layers is developed, based on combining ultra-violet photoemission spectroscopy and essentially damage-free argon gas cluster etching. The efficacy of the technique is shown on several state-of-the-art high-performance photovoltaic systems, with estimated photovoltaic gaps being in excellent agreement with charge transfer state energies, and in direct correlation with corresponding open-circuit voltages. Furthermore, the versatility of the technique is exemplified by its application to study the evolution of the energetic alignment upon environmental degradation, vertical stratification, injection barriers at buried interfaces, side-chain variation, molecular doping and the energetic alignment in ternary blend systems. This work demonstrates the potential and wide applicability of our novel technique for understanding the vertical composition and energetic alignment in organic thin films. This understanding is crucial towards the future development of optoelectronic organic devices.