RESUMO
We study the top surface composition of blends of the conjugated polymer regioregular poly-3-hexylthiophene (P3HT) with the fullerene (6,6)-phenyl-C(61)-butyric acid methyl ester (PCBM), an important model system for organic photovoltaics (OPVs), using near-edge X-ray absorption fine structure spectroscopy (NEXAFS). We compare the ratio of P3HT to PCBM near the air/film interface that results from preparing blend films on two sets of substrates: (1) poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) coated indium tin oxide (ITO) as is commonly used in conventional OPV structures and (2) ZnO substrates that are either unmodified or modified with a C(60)-like self-assembled monolayer, similar to those that have been recently reported in inverted OPV structures. We find that the top surface (the film/air interface) is enriched in P3HT compared to the bulk, regardless of substrate or annealing conditions, indicating that changes in device performance due to substrate modification treatments should be attributed to the buried substrate/film interface and the bulk of the film rather than the exposed film/air interface.
Assuntos
Eletrodos , Fulerenos/química , Polímeros/química , Tiofenos/química , Difração de Raios X/métodos , Desenho de Equipamento , Análise de Falha de Equipamento , Teste de Materiais , Propriedades de SuperfícieRESUMO
Two new conjugated polymers have been designed and synthesized for polymer solar cells. Both of them exhibit excellent photovoltaic properties with a power conversion efficiency as high as 4.74%. Different from the traditional linear donor-acceptor (D-A) type conjugated polymers, these newly designed polymers have a two-dimensional conjugated structure with their tunable acceptors located at the end of D-A side chains and connected with the donors on the main chain through an efficient pi-bridge. This approach provides great flexibility in fine-tuning the absorption spectra and energy levels of the resultant polymers for achieving high device performance.