Autor(es): Nascimento, André Miguel Martins do
Data: 2016
Identificador Persistente: http://hdl.handle.net/10362/20674
Origem: Repositório Institucional da UNL
Assunto(s): Organic solar cells; Degradation; Mobility; Transient photovoltage (TPV); Open-circuit corrected charge carrier extraction (OTRACE); Space charge limited current (SCLC); Domínio/Área Científica::Engenharia e Tecnologia::Engenharia dos Materiais
Organic photovoltaic technology presents itself as a viable and cost-effective re-newable energy. However, efficiency must be further increased if its commercialization is to succeed. As such, the main focus of this thesis is on the transport and recombination dynamics of photo-generated charges, which are key for increasing solar cell efficiency. An understanding of the relationship between characteristic device parameters such as fill factor (FF), open-circuit voltage (VOC) and short-circuit current (JSC) to material proper-ities such as electron and hole mobilities (μn and μp), active layer thickness and the bimo-lecular recombination coefficient (k2), will be developed. The degradation (85ºC in dark-ness for 1000h) of organic solar cells, made with proprietary materials from Heliatek GmbH, is studied through the use of basic (current density – voltage (JV) curve, external quantum efficiency (EQE) spectrum) and transient solar cell characterization techniques (Transient photovoltage (TPV), Suns-VOC, open-circuit corrected charge extraction (OT-RACE), space charge limited current (SCLC)), performed at the Dresden Integrated Cen-ter for Applied Physics and Photonic Materials. Results indicate that the reduction in solar cell efficiency upon aging of the devices is mostly due to a decrease in FF, itself caused primarily by a mobility reduction and parasitic resistances. In an attempt to slow down degradation, the addition of a 5nm protective layer is also studied. While this layer de-creases the FF slightly, a slower degradation of JSC and FF outweights this initial loss in FF.
