Design and Characterization of Organic Solar Cells Based on Non-Fullerene Acceptors

Abstract

The rise in the global population is constantly putting pressure on the available energy resources leading to an excessive exploitation of conventional energy resources such as fossil fuels. The use of fossil fuels has led to several health challenges and environmental issues, this has therefore informed the decision to switch to renewable energy resources. Solar PV technology has carved a niche for itself as a low cost option for providing electricity even to the most inaccessible areas, however convention technologies are relatively limited in their application due to their rigid nature and difficult manufacturing steps. This has created an opportunity for research into materials that can be easily fabricated and used for their photovoltaic effect, hence the recent interest in the field of organic photovoltaics. Organic photovoltaic research has gained momentum since the discovery of conducting polymers and holds a promise for a low cost alternative to conventional PV technologies for providing access to electricity. The challenge currently facing the commercialization of this technology is the very modest efficiencies and lifetimes currently achieved. An improvement in the performance of these devices can be made possible by ensuring proper energy level alignment and matching of donor-acceptor materials that have a wide absorption in the visible range. In this work, AnE-PVstat was investigated for its compatibility with novel acceptor materials, PCE of 0.88 % was obtained with ITIC as against 1.89 % with PCBM the reference sample without a solvent additive. It is also important to note the high Voc of about 1 V obtained with these electron acceptors which is possibly linked to alignment of the HOMO level of the polymer and the LUMO level of the acceptors. It was also discovered that upon utilization of a solvent additive the PCE of devices based on ITIC increased to 0.88% while those for PCBM increased to 2.2 %. This increase in PCE obtained from the use of solvent additive is a critical one as it serves as an indication of the possibility of refining the morphology of the active layer without including an additional annealing step, thereby increasing the efficiency of the roll to roll process for commercialization. The thesis further demonstrated that an electronic compatibility is not sufficient for achieving high performance in solar cell devices but also a morphological compatibility is required.