The development of high efficiency polymer solar cells is a challenging research task and our efforts have, during several years, been concentrated on synthesizing and evaluating new materials. Through the last years considerable effort has been put into decreasing the bandgap of the conjugated polymers with the objective to extend the absorption to longer wavelengths. Thereby, a larger part of the solar spectrum is covered.
Recently we synthesized a blue donor-acceptor copolymer called TQ1, which in hero cells shows maximum power point efficiencies around 6%. This polymer simply consists of thiophenes alternating with substituted quinoxaline units and is easily synthesized in only a few steps. To increase the thermal stability of the active material different methods to stabilize the morphology will be described.
Polymers having new large planar building block will be described, designed to combine many favorable properties that such building blocks can induce. After copolymerization with thiophene, solar cells with thick active layers having decent power conversion efficiency have been prepared.
By using an ultra-thin layer of an uncharged conjugated polymer as cathode interfacial material it is possible to overcome some of the electrical and morphological issues with inverted cells. A systematic investigation has been performed to give a deeper insight regarding the impact of the ultra thin layer on the active layer and on the cathode. The polymer design, synthesis, properties, device structure, and device characteristics will be presented.