高分子太陽能電池中作為主動層的P型共軛高分子，其光電性質可藉由改變結構及分子量而調整。本研究利用8-bis(5-(2-ethylhexyl)
thiophen-2-yl)-2,6-di(thiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene為Donor單元(D)，5,8-dibromo-2,3-bis(4-(hexyloxy)phenyl)pyrido[3,4-b]pyrazine為Acceptor單元(A)，合成出P11共聚物，並在D或A分別接上含有拉電子性的硫烷鏈或氟原子，合成出P12和P14共聚物，或同時接上硫烷鏈和氟原子的P15共聚物，並與本實驗室先前合成沒有thiophene bridge之P9和P10一起探討此六個共聚物的性質及光電表現。結果顯示含有thiophene bridge的P11和P12的共軛長度比P9和P10長，最大吸收波長往長波長移動，因此所組裝的元件有較高的Jsc值；含有拉電子性的氟原子之P15因其分子量最大，吸收係數高，形成主動層時結晶度良好，且與PC61BM形成彼此穿插且各自連續的網狀結構，組裝成元件有最高的Jsc值(11.70 mA/cm2)、FF值(0.53)及光電轉換效率為4.50%。另外，P2和P15共聚物分別可以藉由剛合成的Pd(PPh3)4為催化劑進行聚合反應，以及使用不同的混合溶劑(CHCl3/Hexane和THF/Hexane)進行索式萃取進而得到較高分子量的共聚物，組裝成元件時高分子量共聚物的元件效率(P2:1.67%, P15:4.31%)大於低分子量的元件效率(P2:0.91%, P15:2.43%)。

The photovoltical performance of a P-type conjugated polymer can be tuned by changing the molecular structure and weight. In this study, 8-bis(5-ethylhexyl)thiophen-2-yl)-2,6-di(thiophen-2-yl)benzo[1,2-b:4,5-b'] dithiophene was used as a donor unit and bromo-2,3-bis(4-(hexyloxy) phenyl)pyrido[3,4-b]pyrazine was used as an acceptor to construct the copolymer P11. Furthermore, an electron-withdrawing alkylthio chain was attached on the donor to form P12, or adding electron-withdrawing fluorine atoms on the acceptor to prepare P14. P15 has alkylthio chain on the donor and fluorine on the acceptor. Combining these four new copolymers with P9 and P10 (without thiophenebridge) prepared in our lab before, the properties- photovoltical performance relationship were investigated. The results showed that the conjugation length of P11 and P12 which containing thiophene bridge was longer than P9 and P10, respectively therefore the corresponding solar cells have higher Jsc value. P15 has higher molecular weight, large absorption coefficient, good crystallinity and forms an interpenetrating bicontinuous network when blend with PC61BM. As a result, inverted cell based on P15 copolymer exhibits the highest Jsc value (11.70 mA/cm2), FF value (0.53) and conversion efficiency (4.50%) amongst the copolymers studied in this thesis. In addition, increasing the molecular weight of P2 by using the fresh prepared Pd(PPh3)4 as a catalyst, or by Soxhlet extraction of P15 with high polar solvent. We have proved the copolymers with higher molecular weight have the efficiency (P2:1.67%, P15:4.31%) higher than that of copolymers with lower molecular weight (P2:0.91%, P15:2.43%).

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