Jianhui Hou

Synthesis, Characterization, and Photovoltaic Properties of a Low Band Gap Polymer Based on Silole-Containing Polythiophenes and 2,1,3-Benzothiadiazole

A new low band gap silole-containing conjugated polymer, PSBTBT, was designed and synthesized. Photovoltaic properties of PSBTBT were initially investigated, and an average power conversion efficiency (PCE) of 4.7% with a best PCE of 5.1% was recorded under illumination (AM 1.5G, 100 mW/cm(2)). The response range of the device covers the whole visible range from 380 to 800 nm. These results indicate that PSBTBT is a promising polymer material for applications in polymer solar cells.

A Polybenzo[1,2‐b:4,5‐b′]dithiophene Derivative with Deep HOMO Level and Its Application in High‐Performance Polymer Solar Cells

Although there is a consensus on the development of solar energy as a green energy resource, the importance of development of the polymer solar cell (PSC) has only been realized in recent years owing to its advantages of low cost and flexibility in large-area applications. Bulk heterojunction (BHJ) type polymer solar cells now play a leading role in realizing high power conversion efficiency (PCE). The development of new polymer materials to further improve the efficiencies of BHJ-type PSCs will accelerate their commercial application. At present, P3HT-PCBM-based PSCs (P3HT= poly(3-hexylthiophene), PCBM=methanofullerene (6,6)-phenyl-C61-butyric acid methyl ester) have exhibited high efficiencies of 4–5%. However, the narrow absorption spectrum of P3HT in 300–650 nm is one of the main hindrances to the further improvement of the efficiencies of P3HT-based devices. To overcome this problem, some low-band-gap polymer materials as donors have been synthesized successfully and applied to photovoltaic devices. Large short-circuit current density (Jsc) and higher efficiencies have been demonstrated using this strategy. In spite of the high Jsc achievable with low-band-gap polymers, the device performance suffers owing to the low open-circuit voltage (Voc) of 0.5–0.7 V. According to published models and experimental results, theVoc of a PSC is closely related to the offset between energy levels of the highest occupied molecular orbital (HOMO) of the donor and lowest unoccupied molecular orbital (LUMO) of the acceptor. Thus, to enhance the opencircuit voltage of these devices, some building blocks with lower-lying HOMOs should be introduced in donor molecules to lower their HOMO levels. Polyfluorene and its derivatives are a well-known class of wide-band-gap organic semiconducting materials. Many donor polymers containing fluorene on the main chain were reported to show lower HOMO levels and correspondingly exhibited higher open-circuit voltages. However, the wider band gaps of these polymers resulted in lower values of Jsc and consequently lower efficiencies. To enhance the efficiency, there is a need for a low-band-gap polymers that can have a high Voc. Few polymers with high open-circuit voltages (above 0.8 V) and consequently high PCEs (above 5%) have been reported to date, except for two kinds of polymers, poly[(2,7silafluorene)-alt-(4,7-di-2-thienyl-2,1,3-benzothiadiazole)] (PSiFDBT) and poly[N-9’’-heptadecanyl-2,7-carbazole-alt5,5-(4’,7’-di-2-thienyl-benzothiadiazole) (PCDTBT), both of which contain a fluorene unit in the polymer main chain. Considering the similarity in the molecular structures of PSiFDBTand PCDTBTwith analogous fluorene units in both of their main chains, it is necessary to explore new molecular structures with favorable characteristics for higher opencircuit voltages and conversion efficiencies. Recently, some benzo[1,2-b :4,5-b’]dithiophene-containing polymers were applied to field-effect transistor (FET) and PSC devices (Table 1). 6, 7] A high mobility of 0.15–

Silicon Atom Substitution Enhances Interchain Packing in a Thiophene‐Based Polymer System

A new silole-containing low bandgap polymer is synthesized by replacing the 5-position carbon of PCPDTBT with a silicon atom (PSBTBT). Through experiments and computational calculations, we show that the material properties, particular the packing of polymer chains, can be altered significantly. As a result, the polymer changes from amorphous to highly crystalline with the replacement of the silicon atom.