光交聯碳六十衍生物及聚(3-烷基)噻吩之合成與其在有機太陽能電池之應用

Abstract

本論文分為兩部分探討。第一部分是光交聯碳六十衍生物於高效能反結構太陽能電池之應用，第二部分是可交聯聚(3-烷基)噻吩之合成與其在有機太陽能電池的運用。 第一部分：我們成功合成出三個結構新穎的碳六十衍生物，分別為PCBOD、POFOD 及 PAFOD。三個化合物的支鏈末端皆含有oxetane官能基，在含少量光起始劑下照射紫外光作開環交聯聚合。交聯後形成具有抵抗有機溶劑侵蝕能力的3D網狀結構，可運用在濕式製程的多層反式結構有機太陽能電池元件。在元件導入碳六十衍生物之中間層，該層可提升電子擷取能力、扮演電洞阻擋層、與主動層產生額外異質接面進而增加激子拆解能力，並可誘導主動層產生更有效之縱向梯度微相分離型態。評估這些 n 型材料所使用的有機太陽能電池元件結構為：ITO/TiOx/crosslinked fullerene derivatives/P3HT:PCBM/MoO3/Ag 這些含有光交聯碳六十衍生物之中間層的元件特性如下：PCBOD (Voc = 0.60 V, Jsc = 12.23 mA/cm2, FF = 62 %, PCE = 4.52 %); POFOD (Voc = 0.60 V, Jsc = 12.25 mA/cm2, FF = 61 %, PCE = 4.50 %); PAFOD (Voc = 0.56 V, Jsc = 3.75 mA/cm2, FF = 44 %, PCE = 0.93 %)。藉由導入C-PCBOD及C-POFOD中間層明顯提升光電轉換效率，有別於對照元件(不含光交聯碳六十衍生物)元件效率從3.5 %提升至4.5 %。我們更進一步地將PCBOD運用在以PCPDTBT : PC71BM為主動層材料之元件(ITO/TiOx/C-PCBOD/PCPDTBT:PC71BM/MoO3/Ag)，其PCE與對照元件(不含C-PCBOD中間層)相比，從原本的2.61 %大幅提升至3.95 %，Jsc更高達16.36 mA/cm2。然而在PAFOD的案例裡卻非如此，其Jsc與對照元件相比，從11.64 mA/cm2大幅下降至3.75 mA/cm2，FF從53 %下降至44 %。我們推測pyrazoline的結構扮演一個電子陷阱的角色為整體元件效率降低的主要原因。 第二部分：藉由格林納置換聚合反應，合成出新穎的可交聯聚(3-烷基)噻吩－P3HOT，此材料在長碳鏈末端含有光交聯基團oxetane，目的也在於交聯後可抵抗有機溶劑的侵蝕。我們針對交聯程度對元件的影響有所差異而做出了三種比例 P3HOT-20、P3HOT-10 及 P3HOT-5 (含oxetane官能基之單體為20、10及 5 mol%)。其在元件的作用與第一部分的碳六十衍生物雷同，但運用在正結構上是扮演一個電洞萃取層，提升電洞擷取能力。評估這些 p 型材料所使用的有機太陽能電池元件結構為：(ITO/PEDOT:PSS/C-P3HOT/P3HT:PCBM/Ca/Al)。以P3HOT-10為例，導入C-P3HOT-10中間層之元件表現有別於對照元件(不含C-P3HOT-10中間層)，元件效率從4.13 %下降至2.28 %，Jsc更是從9.86 mA/cm2下降至6.56 mA/cm2。推測是光交聯所需的光起始劑成為一個捕捉電洞的中心，電洞在傳輸的過程中被捕捉態所捕陷造成Jsc大幅下降，也是造成元件整體表現不如預期的主要原因。

The goal of this research is aimed to improve the performance of the polymer solar cell by adding a cross-linked material as an interlayer. The first part of this study, the novel fullerene derivatives (PCBOD, POFOD and PAFOD) functionalized with a dendron containing two oxetane groups as photo cross-linkers, have been rationally designed and synthesized. In situ cross-linking of these three fullerene derivatives was carried out by UV illumination in the presence of a photoacid to generate a robust, adhesive, and solvent-resistant thin film. This cross-linked network enables a sequential active layer to be successfully deposited on top of this interlayer to overcome the problem of interfacial erosion and realize a multilayer inverted device by all-solution processing. The inverted solar cell devices based on an ITO/TiOx/C-PCBOD or C-POFOD/P3HT:PCBM/MoO3/Ag configuration achieve enhanced device characteristics. The PCE have been improved from 3.5 % to 4.5 % after modification with the PCBOD and POFOD interlayer. On top of that, this promising approach can be applied to another inverted solar cell device modified with the C-PCBOD interlayer, ITO/TiOx/C-PCBOD/PCPDTBT:PC71BM/MoO3/Ag, using PCPDTBT as the p-type low-band-gap conjugated polymer. The PCE has been improved from 2.6 % to 4.0 %. This interlayer exerts multiple positive effects on both polymer/C-PCBOD and PCBM/C-PCBOD localized heterojunctions at the interface of the active layer, including improved exciton dissociation efficiency, reduced charge recombination, decreased interface contact resistance, and induction of vertical phase separation to reduce the bulk resistance of the active layer as well as passivation of the local shunts at the TiOx interface. The second part of this study, we synthesized a novel cross-linkable regioregular polythiophene derivative P3HOT via the Grignard metathesis route. The P3HOT was functionalized with oxetane moieties attaching to the polymer backbone via an alkyl spacer. The cross-linkable oxetane groups were polymerized cationically under UV illumination in the presence of a photoacid and the advantages of this cross-linked network were described above. The polymer solar cells were fabricated with the structure of ITO/PEDOT:PSS/C-P3HOT-10/P3HT:PCBM/Ca/Al. For the device with the C-P3HOT-10 interlayer, the results demonstrate substantially declining performance, especially the Jsc decreases from 9.86 mA/cm2 to 6.56 mA/cm2. We speculate the decadence of the performance may result from the ionic photoacid which act as a hole trap, therefore the Jsc decreases significantly. Further work may be expected along the direction of selecting the non-ionic photoacid to reduce the degree of charge trapping.