Guangrui He

Small Molecules Based on Benzo(1,2-b:4,5-b')dithiophene Unit for High-Performance Solution-Processed Organic Solar Cells

Small molecules, namely, DCAO(3)TBDT and DR(3)TBDT, with 2-ethylhexoxy substituted BDT as the central building block and octyl cyanoacetate and 3-ethylrhodanine as different terminal units with the same linkage of dioctyltertthiophene, have been designed and synthesized. The photovoltaic properties of these two molecules as donors and fullerene derivatives as the acceptors in bulk heterojunction solar cells are studied. Among them, DR(3)TBDT shows excellent photovoltaic performance, and power conversion efficiency as high as 7.38% (certified 7.10%) under AM 1.5G irradiation (100 mW cm(-2)) has been achieved using the simple solution spin-coating fabrication process, which is the highest efficiency reported to date for any small-molecule-based solar cells. The results demonstrate that structure fine turning could cause significant performance difference and with that the performance of solution-processed small-molecule solar cells can indeed be comparable with or even surpass their polymer counterparts.

Efficient small molecule bulk heterojunction solar cells with high fill factors via introduction of π-stacking moieties as end group

Three new oligothiophene derivatives with an acceptor–donor–acceptor structure incorporating 1,3-indanedione or the derivative of 1,3-indanedione units as the terminal acceptor groups—DIN7T, DINCN7T and DDIN7T—have been designed and synthesized for solution-processable small molecule BHJ solar cells. The impacts of these different end dye moieties on the optical absorption, solubility, electrochemical properties, morphology, mobility and solar cell performance were studied. All three compounds exhibit broad and highly efficient solar absorption with a low bandgap. The DIN7T-based BHJ solar cell device achieved a PCE of 4.93% and a high fill factor of 0.72, under illumination of AM 1.5, 100 mW cm−2.

Impact of dye end groups on acceptor-donor-acceptor type molecules for solution-processed photovoltaic cells†

Two new oligothiophene derivatives of the acceptor–donor–acceptor type, incorporating double rhodanine or 1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-trione units as the terminal acceptor groups, D2R(8 + 2)7T and DTDMP7T, have been designed and synthesized for solution-processable small molecule BHJ solar cells. The impacts of these different end dye moieties on their optical, electrochemical properties, morphology, mobility and solar cell performance were studied. Both compounds exhibit broad and highly efficient solar absorption with low bandgaps of 1.70 and 1.62 eV for D2R(8 + 2)7T and DTDMP7T, respectively. The D2R(8 + 2)7T and DTDMP7T based BHJ solar cell devices achieved a PCE of 2.46% and 4.05%, respectively, under the illumination of AM.1.5, 100 mW cm−2.

Impact of fluorinated end groups on the properties of acceptor–donor–acceptor type oligothiophenes for solution-processed photovoltaic cells

Two new oligothiophene derivatives with the acceptor–donor–acceptor structure incorporating fluorinated alkyl cyanoacetate units as the terminal acceptor groups, DCAE7T-F1 and DCAO7T-F7, have been designed and synthesized for solution-processable BHJ solar cells. The impacts of these fluorinated end groups on the optical absorption, solubility, electrochemical properties, morphology, surface energy, film forming ability, mobility and solar cell performance were studied. We found that as the fluorinated alkyl length increased, the surface energy decreased and the lipophobicity increased. Due to its high lipophobic property and a problem with its wettability, DCAO7T-F7 was not able to produce a uniform film by spin coating. A power conversion efficiency (PCE) of 2.26% was achieved with an open-circuit voltage (Voc) of 0.83 V, short circuit current (Jsc) of 5.55 mA cm−2 and fill factor (FF) of 0.50 for DCAE7T-F1 based solar cells. The low Jsc suggests that controlling the film morphology and molecular assembly is essential for the performance of these fluorinated small molecules.