Synthesis And Photovoltaic Performances Of Small Molecular Donor Materials For Organic Heterojunction Solar Cells

Organic photovoltaics (OPVs) have been considered to be a promising next-generation green technology to address the increasing worldwide energy problems. The dissertation mainly describes the development and principle of small molecular heteroj unction solar cells, including the relative donor and acceptor materials. It is believed that several requirements should be considered collectively to design small molecules for high-performance and solution-processed solar cells, such as excellent morphology, wide and efficient absorption, matched energy levels with acceptors, planar structure for high hole mobility, good solubility, chemical and thermal stability. Based on these requirements, we designed and synthesized a series of linear donor-acceptor-donor (D-A-A) asymmetric small moleculars containing indoline as the electron-donating unit, and incorporated alkyl-substituted cyclopent dithiophene-based π-conjugated spacers to form an effectively long conjugated acceptor-donor-acceptor (A-D-A) backbone structure.Two novel D-A-A dyes WS-31and WS-32were developed with benzoxadiazole unit as the additional acceptor, indoline as the donor, thiophene as the π-bridge, octyl cyanoacetate or3-ethylrhodanine as the terminal acceptor. As demonstrated, WS-32is more efficient than WS-31. The solution-processed small molecular heterojunction solar cell based on WS-32/PC6)BM achieves the power conversion efficiency (PCE) of1.02%with a short-circuit current (Jsc) of3.40mA cm-2and an open-circuit voltage (Voc) of0.86V. Moreover, the cyclopentyl bithiophene as new π-bridged was introduced in WS-52to improve the hole-transport ability and broaden the absorption spectrum.The acceptor-donor-acceptor (A-D-A) symmetrical donor WS-53has been synthesized, in which2-ethylhexoxy substituted BDT block is utilized as central building block, and3-ethylrhodanine as the terminal unit. The alkyl-substituted cyclopent dithiophene is incorporated, realizing high molar extinction coefficient, and keeping good coplanarity for improving spectral response and photoelectric performance. Solution-processed small molecular heterojunction solar cell based on WS-53/PC71BM achieves PCE of1.03%with Jsc of4.25mAcm-2and Voc of0.94V.