引入不同對稱性烷基側鏈之共軛高分子應用於總體異質接面高分子太陽能電池

Abstract

在此研究中，為了探討改變高分子側位烷基鏈 (alkyl) 結構，對總體異質接面高分子太陽能電池特性的影響。我們將苯并二噻吩 (benzodithiophene, BDT) 在側位接上烷基鏈噻吩基 (alkyl thienyl) 作為電子予體 (donor)，與作為π架橋 (π-bridge) 之噻吩 (thiophene)、作為電子受體 (acceptor) 之苯并呋喃 (benzooxadiazole, BO)為主體。透過改變BDT與BO上之側位烷基鏈為直鏈及支鏈結構，進而合成一系列之主鏈予體－π－受體型 (D-π-A) 共軛高分子，分別為PBDTTC8TBOC8C8 (P1)、PBDTTC8TBOEHEH (P2)、PBDTTC8TBOC8EH (P3)、PBDTTEHTBOC8C8 (P4)、PBDTTEHTBOEHEH (P5)、PBDTTEHTBOC8EH (P6)，並進行高分子物理與化學性質、光電特性、堆疊結構以及表面形貌之系統化比較。 P1在熱穩定性方面表現良好，並且數目平均分子量 (Mn)、重量平均分子量 (Mw) 皆相當高。P1、P2、P3與P4成膜後均傾向面向上 (face-on) 之堆疊結構，故皆有利於載子縱向傳遞，短路電流 (Jsc) 較高。而P2與P3則擁有較低的HOMO能階與較高之開路電壓 (Voc)，分別為0.93 V與0.90 V，能量轉換效率達到6.5%與6.8%。P4在光學性質方面，具有相當廣的吸收光範圍，半高寬 (FWHM) 達217 nm，且起始吸收波長 (λonset) 為706 nm，紅位移 (red shift) 較明顯。此外與碳球PC71BM混摻性質良好，擁有達15.7 mA/cm2的短路電流，以及7.5%之能量轉換效率 (PCE)。

In this study, in order to investigate the characteristics of bulk heterojunction polymer solar cell through changing polymer alkyl side chains, we use benzodithiophene (BDT) with alkyl thienyl side chains as electron donor, thiophene as π-bridge, and benzooxadiazole (BO) as electron acceptor. By changing the alkyl side chains of BDT and BO into linear or branched structure, we synthesize a series of donor-π-acceptor (D-π-A) conjugated polymers－PBDTTC8TBOC8C8 (P1), PBDTTC8TBOEHEH (P2), PBDTTC8TBOC8EH (P3), PBDTTEHTBOC8C8 (P4), PBDTTEHTBOEHEH (P5), PBDTTEHTBOC8EH (P6) respectively. We systematically compare the physical, chemical, photovoltaic, structural packing, and morphological properties. P1 has the highest thermal stability, number-average molecular weights (Mn), and weight-average molecular weights (Mw). P1, P2, P3, and P4 films tend to form face-on packing structures which is beneficial to carrier transfer orthogonally, thus show enhanced shortcut current (Jsc). P2 and P3 have low-lying HOMOs, leading to high open circuit voltage (Voc) which are 0.93 V and 0.90 V, respectively. These high Voc cause P2 and P3 to achieve power conversion efficiency (PCE) of 6.5% and 6.8%. P4 exhibit the widest FWHM owing to its broad absorption range with more obvious red shift, and its λonset is 706 nm. The Jsc and PCE of P4 are 15.7 mA/cm2 and 7.5%.