Efficient Bulk-Heterojunction Solar Cells Based on a Symmetrical D-π-A-π-D Organic Dye Molecule

A symmetrical D-pi-A-pi-D organic dye molecule 2-{2,6-bis-[2-(4-diphenylamino-phenyl)-vinyl]-pyran-4-ylidene}-malononitrile (DADP) has been introduced into solution-processable organic solar cells (S-P OSCs). Detailed investigations on the relationship between its molecular structure and thermal, photophysical, electrochemical properties and electronic structure are described. The optimized bulk heterojunction solar cell based on DADP as donor and PCBM as acceptor with the configuration of ITO/PEDOT/DADP:PCBM/LiF/Al exhibits a Voc of 0.98 V, Isc of 4.16 mA/cm(2), FF of 0.37, and power conversion efficiency (PCE) of 1.50% under the illumination of AM 1.5 simulated solar light (100 mW/cm(2)). It was noted that the PCE of the device based on DADP is almost double that of the device based on TPA-DCM-TPA, an analogue of DADP, although there is only a small difference between their molecular structures; DADP has a shorter distance between the triphenylamine (TPA) group and the 2-pyran-4-ylidenemalonitrile (PM) group than TPA-DCM-TPA. This small structural difference results in a lower-lying highest occupied molecular orbital (HOMO) energy level and higher hole mobility in DADP, and ultimately leads to the increased PCEs of the DADP-based devices.