含苯并呋喃之主鏈施體-受體型共軛高分子之合成與分析及其異質接面太陽能電池之應用

Abstract

本論文目的為發展新型主鏈予體－受體型共軛高分子於異質接面太陽能電池之應用。我們首先合成一具強拉電子能力及高平面性之苯并呋喃(benzo[c][1,2,5]oxadiazole)基團及一推電子基團苯并二噻吩(benzo[1,2-b:4,5- b′]dithiophene)於主鏈之共軛高分子PBDTBO，並藉由導入烷氧基於苯并呋喃片段，藉此提升高分子之溶解度，此高分子具有良好之熱穩定性，相當高之分子量(Mn=62 kg mol-1)，優良之溶解度及較低之最高填滿分子軌域能階(-5.27eV)，在製成太陽能電池元件後，不需經由退火或添加劑之處理即具有相當之開路電壓為0.86 V與能量轉換效率為5.7%。我們接著合成一系列含噻吩衍生物為推電子基團，苯并呋喃為拉電子基團之結晶性高分子—PTHBO、PBTTBO、PTTTBO，此系列高分子具有高度結晶特性，與低的最高填滿分子軌域能階(5,.47eV)，其太陽能電池元件可獲得開路電壓為1.02 V，且由於其高度結晶特性，其中PBTTBO可得一相當高之填充因子(FF=74%)，在經由添加劑之修飾後，PTTTBO可得一能量轉換效率為5.3%。隨後我們利用一強推電子基團并雙噻吩及其衍生物為電子予體，與苯并呋喃進行聚合，合成出一系列具寬廣吸收(350至700奈米)，良好熱穩定性之高分子—PCyTBO、PCySiTBO、PCyNTBO，其中PCySiTBO亦具有結晶之特性，在製成太陽能電池元件後，由於其寬廣之吸收範圍有利於吸收較多之光子並產生較高之光電流(13.8 mA cm-2)其能量轉換效率可達5.0%。最後我們進一步利用弱推電子基團與強拉電子基團之設計概念合成出一系列弱推電子基團咔唑及茀衍生物與苯并呋喃聚合之高分子，PFTBO、PAFTBO、PCTBO，此系列高分子成功降低最高填滿分子軌域能階，並在製成高分子太陽能電池元件後得到相當高之開路電壓(PFTBO, 1.04 V; PAFTBO, 0.97 V; PCTBO, 0.98 V)，且不需經由退火或添加劑之處理即可得一能量轉換效率為4%。

The objective of this thesis is to develop new main chain donor–acceptor (D–A) conjugated polymers for bulkheterojunction (BHJ) solar cell applications. First of all, we have used Stille coupling to prepare a low-bandgap conjugated polymer, PBDTBO, featuring alternating benzo[1,2-b:4,5- b′]dithiophene (BDT) and 5,6-bis(octyloxy)benzo[c][1,2,5]oxadiazole (BO) units in its backbone, This polymer exhibited good thermal stability, acceptable solubility, high molecular weight (Mn = 62 kg mol–1), and a low HOMO energy level(-5.27 eV). A BHJ polymer solar cells incorporating PBDTBO and PC61BM (blend weight ratio, 1:1), prepared without requiring special treatment, exhibited a high open-circuit voltage (0.86 V) and a high solar energy PCE (5.7%). Second, We have used Stille coupling polymerization to prepare a series of new crystalline, conjugated polymers—PTHBO, PBTTBO, and PTTTBO—featuring alternating thiophene-based building blocks and BO units in their backbones. These polymers possess excellent crystallinity, thermal stability and low-lying HOMO energy levels (-5.47eV). These desirable properties make PTHBO, PBTTBO, and PTTTBO promising materials for solar cell applications. A device incorporating PTTTBO and PC61BM (blend weight ratio, 1:1), with DIO (0.5 vol%) as an additive, exhibited a high value of Voc of 0.87 V and a PCE of 5.3%. Subsequently, We have used Stille coupling polymerization to prepare a series of new crystalline, conjugated polymers—PCyTBO, PCySiTBO, and PCyNTBO—featuring alternating C-, Si-, and N-bridged dithiophene-based building blocks and BO units in their backbones. These polymers exhibit broad absorption (350 to 700 nm) and good thermal stability, and PCySiTBO possess good crystallinity, making them promising materials for solar cell applications. A device incorporating PCySiTBO and PC71BM (blend weight ratio, 1:1), with DIO (2 vol%) as an additive, exhibited a value of Voc of 0.64 V, a value of Jsc of 13.8 mA cm–2, a FF of 0.57, and a PCE of 5.0%. Finally, We have used Suzuki coupling polymerization to prepare a series of new conjugated polymers—PFTBO, PAFTBO, and PCTBO—featuring alternating 9,9-dialkylfluorine, alkylidene fluorine and N-alkyl-2,7-carbazole units as weak electron-rich building blocks and BO units as the electron-deficient acceptors in their backbones. The successfully lowered HOMO energy levels translated into high open circuit voltage of BHJ photovoltaic devices fabricated from blend of these polymers with PCBM (PFTBO, 1.04 V; PAFTBO, 0.97 V; PCTBO, 0.98 V). A device incorporating PCTBO and PC61BM (blend weight ratio, 1:1), exhibited a high value of Voc of 0.98 V, a value of Jsc of 7.2 mA cm–2, a FF of 0.58, and a PCE of 4.1% without any post treatment.