| Summary: | 碩士 === 國立臺北科技大學 === 有機高分子研究所 === 105 === The aim of this study is to investigate the photovoltaic performance of three new two-dimensional conjugated polymers (P1- P3) used as electron donor blending with PC70BM to form the photoactive layer of bulk-heterojunction solar cells. Compared with commercially available P3HT donor material, the two-dimensional conjugated polymers exhibit several advantages such as broad absorption in the near IR region and low optical bandgap. Moreover, the two-dimensional conjugated polymers have relatively low HOMO level which is beneficial to obtaining high open-circuit voltage solar devices. In this work, a series of new 2D conjugated polymers, P1-P3, containing bithiophene donor unit with/without fluorine atom, benzothiadiazole (BTD) acceptor unit which bears vinyl-terthiophene side chain, and thiophene π-spacer were designed and synthesized. The polymer P2 showed a deep HOMO energy level of -5.4 eV, which is lower than that (-5.0 eV) of polymer P1 due to strong electron-withdrawing nature of fluorine atom presenting in the bithiophene moieties. The introduction of thiophene π-spacer into the backbone of polymer P3 slightly up-shifts the HOMO level.
After optimization of blend ratio of donor/acceptor (D/A) and the amount of DIO additive, the average power conversion efficiency of the solar devices based on P1, P2 and P3 were determined to be 1.55%, 0.79% and 6.14%, and the highest PCEs of P1, P2, P3 were 2.22%, 0.95%, 6.66%, respectively. The TEM micrographs of P1/PCBM and P2/PCBM blends indicated relatively large domain sizes due to the formation of PCBM clusters, leading to the reduction of interface between donor and acceptor, extremely unbalanced electron and hole mobilities and boosted recombination rate of charge carriers. On the other hand, the P3/PCBM blend exhibit a nano-scale bi-continuous netwrok morphology; therefore, the P3-device has a high Jsc and a large FF.
Further, we investigated the effects of PEIE cathode interlayer on the highest photovoltaic performance of P3-based devices. Addition of PEIE interlayer between the ITO conductive glass and ZnO, the photovoltaic performance of Jsc and F.F. were successfully increased from 12.99 mA/cm2 and 59.22% to 13.51 mA/cm2 and 60.64%, respectively.
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