具有在氧化鈦上形成自組裝單層結構及交聯特性之碳六十衍生物其在反式高分子太陽能電池之應用；摻混含有五氟苯基之碳六十衍生物於穩定有機太陽能電池形貌之研究

Abstract

本論文分為兩大主題，第一部分為具有在氧化鈦上形成自組裝單層結構及交聯特性之碳六十衍生物在反式高分子太陽能電池之應用，第二部分為摻混含有五氟苯基之碳六十衍生物於穩定高分子太陽能電池形貌之研究。 第一部分:將兩具有oxetane官能基修飾之碳六十衍生物- [6,6]-phenyl-C61-butyric oxetane ester (PCBO) 以及 [6,6]-phenyl-C61-butyric oxetane dendron ester (PCBOD) 引入反結構高分子太陽能電池的應用中。從表面接觸角(surface contact angle)及X射線光電子能譜(XPS)的結果可發現具有中性特性的oxetane可利用加熱、照光在氧化鈦表面做陽離子開環反應產生鍵結。在修飾一個oxetane官能基的PCBO材料方面，其可與氧化鈦表面-OH基團形成單層自組裝結構。在反結構混摻系統元件B (ITO/TiOx/SA-PCBO(self-assembled PCBO)/P3HT:PCBM(1:1 w/w)/MoO3/Ag)效率可達到4.1%，相對於沒有做任何修飾的標準元件A (ITO/TiOx/P3HT:PCBM (1:1 w/w)/MoO3/Ag)效率3.6%有明顯地提升。其元件表現提升的原因在於其提升了激子拆解的效率以及降低載子再結合的機會，減少介面電阻，且由於自組裝產生的鍵結，覆蓋掉氧化鈦表面的捕捉電子缺陷，因此效率有顯著地提升。具有兩個oxetane官能基的PCBOD，其不僅具有與氧化鈦表面形成自組裝的功能，且分子間會交聯形成一緊密且堅固的結構。又交聯的PCBOD為多分子層結構，因此其可以避免PCBO單分子結構覆蓋不完全，造成缺陷的缺點，在修飾PCBOD材料的元件C(ITO/TiOx/C-PCBOD(crosslinking PCBOD) /P3HT:PCBM(1:1, in wt% )/MoO3 /Ag)，其效率更高達4.5%。 第二部分:近期在有機太陽能電池元件的研究中，傳統的P3HT:PCBM的混摻系統元件，其主動層形貌的熱不穩定性為大家廣為探討的議題。隨著對元件施加熱能，主動層內具有較高分子遷移率的球狀碳六十分子，會自發的擴散聚集，造成較大團簇甚至單晶結構，形成較差的相分離尺度，而此不適當的相分離尺度會影響主動層內激子的擴散及載子的傳遞。在我的研究中，設計一具有五氟苯基取代的碳六十衍生物-[6,6]-phenyl-C61-butyric pentafluorophenyl ester (PCBFP)，將其摻入P3HT:PCBM的混摻系統中，利用五氟苯基與碳六十之間的作用力做物理性的聚合，進而鞏固主動層的形貌，達到長時間熱穩定的效果。在混摻系統為P3HT:PCBM:PCBFP(重量比例為6:5:1)的元件表現中，在150℃下加熱25小時，其效率可高達3.7%。

This research contains two independent parts, the first part is self-assembled and cross-linked fullerene interlayer on titanium oxide for highly efficient inverted polymer solar cells, and the second part is morphological stabilization by incorporation of a pentafluoro phenyl-containing fullerene for highly stable oganic solar cells. In first part, we used two oxetane-functionalized fullerene derivatives, [6,6]-phenyl-C61-butyric oxetane ester (PCBO), and [6,6]-phenyl-C61-butyric oxetane dendron ester (PCBOD) in the inverted solar cells to achieve higher power conversion efficiency. We demonstrated that the oxetane functionality with neutral nature can anchor onto the TiOx surface via cationic ring-opening reaction under thermal and UV treatment, as evidenced by the contact angle measurement and x-ray photoelectron spectroscopy. The self-assembly of PCBO, functionalized with one oxetane group, on the TiOx surface forms an adhesive monolayer with intimate contact. Inverted bulk-heterojunction device B (ITO/TiOx/SA-PCBO/P3HT:PCBM(1:1, w/w)/MoO3/Ag) with this self-assembled PCBO (SA-PCBO) modifier showed an impressive power conversion efficiency of 4.1%, which outperforms the reference device A (PCE = 3.6%) without this monolayer (ITO/TiOx/P3HT:PCBM(1:1, w/w)/MoO3/Ag). This SA-PCBO modifier exerts multi-positive effects on the interface, including improvement of exciton dissociation efficiency, reduction of charge recombination, decrease of the interface contact resistance and passivation of the surface electron-traps at the interface of TiOx. Furthermore, PCBOD, containing two oxetane groups, is capable of self-assembling on the TiOx surface and simultaneously undergoing cross-linking, generating a dense, robust and pinhole-free multi-molecular interlayer to further strengthen the interface characteristics. Device C (ITO/TiOx /C-PCBOD/P3HT:PCBM(1:1, in wt%)/MoO3/Ag) incorporating this cross-linked PCBOD (C-PCBOD) interlayer delivered the highest PCE of 4.5% which represents 26% enhancement over device A. This simple and easy strategy smartly integrates the advantages of self-assembly and cross-linking in a single fullerene-based molecule, showing promise in producing highly efficient inverted PSCs. A primary area of concern for traditional P3HT:PC61BM system is the morphological instability. Upon heating, spherical PCBM with high molecular mobility tends to diffuse out of the P3HT matrix and aggregate into larger cluster or single crystals. Such a progressive phase-segregation eventually leads to micron-sized D-A domains with concomitant reduction of device efficiency. In the second part, we have designed a pentafluorophenyl-containing fullerene -[6,6]-phenyl-C61-butyric pentafluorophenyl ester (PCBFP) which was doped into the P3HT:PC61BM active layer to form a ternary blending system. Physical polymerization through the attractive quadrupole-quadrupole interaction between pentafluorophenyl groups and C60 core-structure was demonstrated to effectively prevent the thermal-driven phase separation. The device based on the P3HT:PCBM:PCBFP(6:5:1 in wt %) blend showed extremely stable device characteristics, delivering an average power conversion efficiency (PCE) of 3.7 % during the long-term thermal heating at 150 ℃ for 25 hours.