高效率太陽能電池用低能隙共軛高分子及碳六十衍生物之合成

Abstract

近來大量的低能隙(Low Band Gap，LBG)共軛高分子被合成出來，是為了可吸收更多紅光與紅外光區的光子，藉此增加高分子太陽能電池(Polymer Solar Cell， PSC)的光電流，本計畫研究目的為利用本實驗室自行開發出的高效率低能隙共軛高分子做為P型材料，再混合N型材料[6,6]-phenyl-C61-butyric acid methyl ester(PC61BM)或[6,6]-phenyl-C71-butyric acid methyl-ester (PC71BM)成元件之主動層，最後結合可熱交聯之碳六十衍生物 (PCBSD)做為陰極修飾層，藉以達到高光 電轉換效率之太陽能電池。 本計畫中的高分子材料是以氟化的5,6-difluorobenzo[c][1,2,5] thiadiazole (FBT) 與5,6-difluorobenzo[c][1,2,5]selenadiazole (FBS)為主體做為電子受體(Electron Acceptor)，多電子的thiophene或 selenophene為電子給體(Electron Donor)，將受體與給體進行聚合反應即可得到低能 隙共軛高分子材料(P1、P2與P3) (如圖一)；實驗中採用氟化的FBT與FBS，此可以利用氟原子的拉電子效應使得高分子材料之HOMO能階下降，藉此增加太陽能電池元件之開路電壓，另一 方面，selenophene 比 thiophene 的電子密度高，因此可以使得高分子材料的吸光更加紅位移，藉以增加太陽能電池元件之短路電流，這些材料具有結晶之特性，因此有高的電洞遷移率，可以提升太陽能電池元件之填充因子。 製備完成的高分子材料可以製作成反式太陽能電池的結構 (ITO/ZnO/active layer/ PEDOT：PSS or MoO3/Ag)，再運用先前已在本實驗室中證實過的可熱交聯之碳六十衍生物(PCBSD)碳六十衍生物，藉由旋轉塗佈將其塗佈於氧化金屬層表面，做為陰極修飾層，此修飾層的優點為：一) 提升電子擷取能力；(二) 扮演電洞阻擋層；(三) 熱點鈍化（hot spot passivation）降低漏電流，因此可以再提升太陽能電池元件之光電流與填充因子，進而提升光電轉換效率。

Recently, many low band gap (LBG) copolymers have been synthesized in order to absorb more infrared photons than P3HT. Furthermore, they can improve the short circuit currents of polymer solar cells (PSCs). In this project, fluorine substituted 5,6-difluorobenzo[c][1,2,5]thiadiazole (FBT) or 5,6-difluorobenzo[c][1,2,5]selenadiazole (FBS) as an electron acceptor were copolymerized with thiophene or selenophene as an electron donor to form low band gap copolymers (P1、P2 and P3) (Figure 1.). It will be expected fluorine atoms induce the lower-lying HOMO levels of these copolymers and enhance open-circuit voltages of PSCs. On the other hand, copolymers containing selenophenes have more red-Shift absorption than copolymers containing thiophene due to highe electron density of selenophene. Finally, bulk heterojunction photovoltaic cells were fabricated on the basis of ITO/ZnO/ active layer/ PEDOT:PSS or MoO3/Ag) configuration. Furthermore, cross-linked fullerene material as an interlayer was also applied to these copolymers to achieve high power conversion efficiencies.