| Summary: | 碩士 === 國立臺北科技大學 === 有機高分子研究所 === 100 === In this study, we mainly focus on studying the effect of structure of fullerene derivatives on the photovoltaic performance of polymer solar cells. In the first part, poly(3-hexylthiophene) (P3HT) and C60 derivatives were employed as an electron donor and an electron acceptor, respectively, to fabricate polymer solar cells. It has been established that the open-circuit voltage (Voc) is determined by the difference of the HOMO level of the donor and the LUMO level of the acceptor, and the up-shift of the acceptor''s LUMO can potentially raise the Voc. Although chemically grafting electron donating groups on the C60 cage may enrich the electron density of C60 core and thereby increase the LUMO, the sp3-sp3 orbital of the bridged carbon significantly blocks the resonance of electron from the electron-rich substituent to C60, leading to a minor effect on the LUMO. In this research, new fullerene derivatives bearing triphenylamine, carbazole or fluorine moiety were utilized as the acceptor of P3HT to prepare bulk-heterojunction solar devices. The cyclic voltammetry measurements show these fullerene derivatives have a similar LUMO as that of PCBM. However, the Voc of the devices based on these acceptors is much higher than that of the device based on PCBM. This finding provides a new avenue to design next-generation C60-derived acceptor for the development of high-Voc polymer solar cells.
In the second part, the use of fulleropyrrolidine derivatives bearing electron donating moieties as an acceptor in P3HT-based solar cells results in unfavorable S-shaped current density-voltage (J-V) curves. With the aid of processing additive and the introduction of a P3HT film as a buffer layer, the fill factor can be greatly improved. Especially, the inverted solar devices using the above fullerene derivatives as an acceptor exhibit normal J-V curves with high fill factor and outstanding power conversion efficiency. These observations suggest these fullerene adducts may form molecular aggregation that induce vertically inhomogeneous distribution of these compounds, and they can be adapted as effective acceptor materials for inverted polymer solar cells.
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