合成與分析予體受體型共軛高分子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。我們首先合成一系列具拉電子基團及高平面性苝二醯亞胺(perylene diimide)基團於側鏈之共軛高分子，導入此機團於側鏈可使高分子具發光淬息(quenching)特性及有效之電子轉移過程，因此其太陽能電池元件具有提升之光電流。我們接著合成一系列含強拉電子基團吡啶并[2,3-b]吡嗪(pyrido[3,4-b]pyrazine)之主鏈予體－受體型共軛高分子，藉由導入具不同供電子能力之并雙噻吩基團有效調控高分子之能隙(bandgap)，使高分子具有低能隙及寬廣之吸收範圍350~800奈米，有利於大量光子之吸收，其中以一三成分高分子製作太陽能電池元件可獲得高光電流(short-circuit current)為10.85 mA/cm2及不錯之能量轉換效率為3.15%。隨後我們藉由將一缺電子噻吩并雙酮吡咯(thieno[3,4-c]pyrrole-4,6-dione)單元共軛一多電子雙噻吩片段合成一新穎予體－受體共軛高分子，此高分子具有高結晶性可利於電荷之傳輸，以此高分子製作太陽能電池可獲得高開路電壓(open-circuit voltage)為0.95 V與高能量轉換效率為4.7%. 我們進一步將此缺電子雙酮吡咯單元與具多電子且含矽原子之并雙噻吩片段結合以合成具結晶性及低能隙特性之新型予體－受體共軛高分子。此含矽高分子於製作太陽能元件後可展現能量轉換效率為3.42%。

The objective of this thesis is to develop new donor–acceptor (D–A) conjugated polymers for bulkheterojunction (BHJ) solar cell applications. First of all, we have used Suzuki coupling to prepare a series of donor–bridge–accptor copolymers, comprising the conjugated cyclopentadithiophene-carbazole main chains and the pendent perylene diimide (PDI) side chain. We observed quenching in the photoluminescence spectra of the copolymers after incorporating the electron-deficient PDI moieties on the polymer side chains, indicating the occurrence of efficient photoinduced electron transfer. The photovoltaic devices based on the PDI-containing polymers revealed significantly enhanced photocurrents as a result of the presence of PDI moieties. Second, we have used Stille polymerization to prepare a series of low-bandgap copolymers, P1–P4, by conjugating the electron-withdrawing pyrido[3,4-b]pyrazine (PP) moieties with the electron-rich benzo[1,2-b:3,4-b´]dithiophene (BDT) or cyclopentadithiophene (CPDT) units. The two donors possessing different electron-donating abilities were used to tune the optical bandgaps and energy levels of the resultant polymers. The three-component copolymers P3 and P4 containing the thiophene and bithiophene segments, respectively, can provide not only broad spectral absorption ranges from 350 to 800 nm but also homogeneous morphologies when blended with [6,6]-phenyl-C70-butyric acid methyl ester (PC70BM). An optimal photovoltaic device incorporating the P4:PC70BM blend at a weight ratio of 1:4 displayed a short-circuit current (Jsc) of 10.85 mA cm–2 and a power conversion efficiency (PCE) of 3.15%. Subsequently, we prepared a new donor–acceptor polymer PBTTPD through conjugating the electron-rich bithiophene donor with the electron-deficient thieno[3,4-c]pyrrole-4,6-dione (TPD) acceptor. PBTTPD exhibits high crystallinity and a low-lying highest occupied molecular orbital (HOMO). An optimal photovoltaic device incorporating a PBTTPD/[6,6]-phenyl-C61-butyric acid methyl ester blend at a weight ratio of 1:1.5 displayed an large open circuit voltage (Voc) of 0.95 V and an excellent PCE of 4.7%. Finally, we synthesized two new low-bandgap polymers PCPDTTPD and PDTSTPD through combining the electron-deficient TPD moieties with the coplanar, electron-rich cyclopenta[2,1-b:3,4-b´]dithiophene (CPDT) or dithieno[3,2-b:2´,3´-d]silole (DTS) units, respectively, to reach narrow optical bandgaps. PCPDTTPD and PDTSTPD differ merely in terms of their bridging atom—carbon and silicon on their corresponding CPDT and DTS donors. Both polymers exhibited excellent thermal stabilities, crystalline characteristics, broad spectral absorptions, and low-lying HOMO energy levels. Notably, the presence of silicon atoms along the chain of PDTSTPD resulted in that having a lower-lying HOMO energy level and a higher hole mobility relative to those of PCPDTTPD. A device incorporating the PCPDTTPD:PC71BM blend (1:4, w/w) provided a power conversion efficiency of 2.15%, whereas that for a device incorporating the PDTSTPD:PC71BM blend (1:1, w/w) was higher at 3.42%.