Three novel solution processable organic small molecules, TPT-N, TPT-S and TPT-D with a Donor-Acceptor-Donor( D-A-D) structure based on thiophene donor unit and 2-pyran-4-ylidenemalononitrile (PM) acceptor unit, were designed and synthesized. Effect of alkyl chain number on the solubility, photo-physical properties(absorption characteristic) , thermal stability and photoelectric properties of the molecules were investigated. The results indicate that with the alkyl chain increasing the solubility and film-forming properties of the molecules increase, and the absorption spectra of the organic small molecules are red-shifted in solutions and the absorption bands in films become narrow. Moreover, the highest occupied molecular orbital( HOMO) energy levels also increase with the alkyl chain of the molecules increasing. Bulk heterojunc-tion structural solar cells with a device structure of ITO/PEDOT : PSS/D-A-D : PCBM/LiF/Al based on the D-A-D organic small molecules as the donor,(6,6)-phenyl C61-butyric acid methyl ester(PCBM) as the acceptor were fabricated. It is found that the device based on TPT-S which has a single alkyl chain on the thiophene unit has a relatively high power conversion efficiency (PCE). The research results confirm that the alkyl chain number is one of the most important effects that influence the properties of the materials and device per-for-mance as for D-A-D organic small molecular solar cell materials.
Donor-Acceptor-Donor(D-A-D)Organic small moleculeAlkyl chainSolar cell
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