Novel Polyhedral Oligomeric Silsesquioxanes-poly(Ethylene Oxide) Hybrid Nanoparticles As Cathode Interfacial Layer Applied To The Organic Solar Cells

Compared with the inorganic solar cell, organic solar cells has attracted anincreased attention because of the low cost facilitate, convenient preparation and theflexible substrate. Currently, organic solar cells based on conjugated polymers aselectron donor and fullerene derivatives as electron acceptor the power conversionefficiency (PCE) exceeded10%. However, compared with the inorganic solar cells,the power conversion efficiency of the organic polymer solar cell is still lower, it isalso a great impact on the development and commercialization. Therefore, how toimprove the efficiency of organic solar cells is still to research.The polyhedral oligomeric silsesquioxanes (POSS) is a typical hybridorganic-inorganic nanostructure, consisting of a silicon oxide cage with an organicsubstituent. The poly(ethylene oxide)-polyhedral oligomeric silsesquiox-ane(POSS-PEO) nanoparticles containing branched PEO having a low surface energy,easy migration characteristics. It has been used in the lithium battery to improve theperformance of the cells. However, the POSS-PEO molecules used in organic solarcells, especially cathode buffer layer to improved the performance has not beenreported in the literature.In the dissertation, the POSS-PEO nanoparticles was added in the poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) solution of thesolar cells, The result show that the POSS-PEO namoparticles could migrate to thesurface of the active layer as a cathode buffer layer. After when the POSS-PEOcontent of3.0wt%and thermally annealed150oC for10min. the efficiency of thesolar cell device corresponding to the highest power conversion efficiency (PCE) of3.6%, but the thermally annealed pure P3HT: PCBM system device efficiency was2.8%. As demonstrated by the scanning electron microscopy (SEM) and atomic forcemicroscope (AFM) results, POSS-PEO nanoparticles could aggregate and migrateonto the surfaces of the active layer via self-assembly, especially after thermal annealing treatment150oC, the POSS-PEO could form one thin layer. Moreover, bythe ultraviolet photoelectron spectroscopy (UPS) found the work function of Alelectrode decreased from4.3eV to3.8eV, indicating that POSS-PEO nanoparticlesbuffer layer could facilitating the Ohmic contact between the active layer and Alelectrode, and to improve the performance of the organic solar cells. Meanwhile, theUV results show the existence of POSS-PEO facilitated the crystallization of P3HTduring the film forming process.