主鏈予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

本論文主要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。首先我們合成一具有并雙噻吩(cyclopentadithiophene)與吡咯并吡咯二酮(diketo-pyrrolo-pyrrole)基團於主鏈之共軛高分子，并雙噻吩與吡咯并吡咯兩者皆具有平面性之結構，因此可增加兩者間的分子內電荷傳送並延長有效共軛長度，藉此達到低能隙(1.3 eV)之效果。其元件在掺混碳球衍生物後，具有寬廣之吸收範圍350~1000奈米，有利於吸收較多的光子並產生較高之電流(10.87 mA cm-2)與2.27%之能量轉換效率。接著我們成一新的拉電子基團噻二唑/苯并噻二唑 (thiadiazole/benzoimidazole)並與咔唑(carbazole)共軛合成一共軛高分子。此高分子具有一接近太陽能譜最大光通量處之能隙(1.75 eV)，且與碳球之間具有適當的最低未填滿軌域能階差，其元件的能量轉換效率為1.8%。接著我們藉由多電子基團雙噻吩并二噻吩(2,5-di(thiophen-2-yl)thieno[2,3-b]thiophene)與缺電子基團噻吩并雙酮吡咯(thieno[3,4-c]pyrrole-4,6-dione)合成一新穎的共軛高分子，由於強拉電子基團噻吩并雙酮吡咯之存在，使得此高分子具有高結晶特性與低的最高填滿分子軌域能階，其太陽能電池元件可獲得開路電壓為0.85 V與高能量轉換效率為5.1%。最後我們進一步將此缺電子基團噻吩并雙酮吡咯與多電子基團噻吩合成一系列高分子，這些高分子亦具有結晶特性與低的最高填滿分子軌域能階。具有己烷-噻吩與噻吩并雙酮吡咯之共軛高分子，在製成太陽能電池元件後，其具有高開路電壓為0.96 V與能量轉換效率為2.6%。

The objective of this thesis is to develop new main chain donor (D)-acceptor (A) conjugated polymers for bulk heterojuncttion (BHJ) solar cells. First of all, We have synthesized a narrow-bandgap conjugated polymer (PCTDPP) containing alternating cyclopentadithiophene (CT) and diketo-pyrrolo-pyrrole (DPP) units by Suzuki coupling. This PCTDPP exhibits a low band gap of 1.31 eV and a broad absorption band from 350 to 1000 nm, which allows it to absorb more available photons from sunlight. A bulk heterojunction polymer solar cell incorporating PCTDPP and C70 at a blend ratio of 1:3 exhibited a high short-circuit current (Jsc) of 10.87 mA cm–2 and a power conversion efficiency (PCE) of 2.27%. Second, we synthesized a new polymer, PCTDBI, containing alternating carbazole and thiadiazole-benzoimidazole (TDBI) units. This polymer which features a planar imidazole structure into the polymeric main chain, possesses reasonably good thermal properties and an optical band gap of 1.75 eV that matches the maximum photon flux of sunlight. Electrochemical measurements revealed an appropriate energy band offset between the lowest unoccupied molecular orbital energy level of polymer and that of PCBM, thereby allowing efficient electron transfer between the two species. A solar cell device incorporating PCTDBI and PC71BM (1:2, w/w) exhibited a PCE of 1.84%. Third, we prepared a new donor-acceptor polymer, PDTTTPD, through conjugating the electron-rich 2,5-di(thiophen-2-yl)thieno[2,3-b]thiophene (DTT) and electron-deficient thieno[3,4-c]pyrrole-4,6-dione (TPD) acceptor. PDTTTPD exhibited high crystallinity and low-lying HOMO energy level due to presence of strongly electron-withdrawing TPD units. A device incorporating PDTTTPD/PC71BM with DIO (1 vol%) as an additive, exhibited open-circuit voltage (Voc) of 0.85V and PCE of 5.1%. Finally, we synthesized two new crystalline polymers (PT6TPD and PT8TPD) containing alternating thiophene and thieno[3,4-c]pyrrole-4,6-dione (TPD) units by Stille cross-couling copolymerization. Both polymers possess excellent thermal stability, crystallinity, and low-lying HOMO energy level because of presence of rigid and planar electron withdrawing units (TPD) in polymeric backbone. A device incorporating the PT6TPD:PC71BM blend (1:1, w/w) exhibit high Voc of 0.96 V and PCE of 2.6%.