富勒烯衍生物於高分子太陽能電池之應 富勒烯衍生物於高分子太陽能電池之應 富勒烯衍生物於高分子太陽能電池之應 富勒烯衍生物於高分子太陽能電池之應 用

Abstract

碳球材料被廣泛的運用於太陽能電池之中，主要的原因是碳球擁有許多優越的特性，譬如像是快速傳遞電子的能力和適當的最低電子未填滿能階等特性。在第二章，我們設計合成一系列以雙苯環為外側官能基團基礎的雙取代碳六十衍生物。和PC61BM的最低電子未填滿能階互相比較，新的雙取代碳六十衍生物展現較高的電子能階約−3.85 eV。外側官能基的苯環平面和碳六十表面平行，使得碳六十之間的作用力下降，但對碳六十的電化學特性的影響不大。最重要的是，這個特殊的立體結構保護碳六十，抑制了分子聚集也提升了分子本身的溶解度，並且展現了非結晶的特性。以P3HT:DMPCBA為基礎的元件，Voc的表現為0.87 V，Jsc為9.05 mA/cm2，FF為65.5%，效率為5.2%。 外側的官能基減弱碳六十之間的作用力也造成了電子傳遞能力的下降。在第三章，我們設計合成一系列分別以苯環和甲基，噻吩和甲基為外接官能基的雙取代碳球衍生物。小而緊密的外側基團提升了碳球之間的作用力，但也造成了相分離的現象。這個不良的薄膜型態可以藉由外加溶液添加劑來改善。在添加劑的幫助之下，以P3HT/MTC60BA為基礎的元件，在效率表現的參數上都有明顯地提升，在Voc的表現為0.78 V，Jsc為9.04 mA/cm2，FF為69.8%，效率為4.92%。最重要的是，這個添加劑對於我們的雙取代碳球衍生物都有正面的作用。 雙取代碳球衍生物是由立體異構物所構成的混合物，這些異構物擁有互異的最低電子未填滿能階和不同的立體幾何結構，可能會對薄膜型態和元件表現有所影響。為了去調查異構物的效應，我們分別利用韁繩法和傳統的合成方法來合成雙取代碳球衍生物 (APM-CBA)。相較之下，R-APM-CBA比S-APM-CBA有更好的Jsc和FF值和效率表現。同樣地，在電子傳遞速度上，R-APM-CBA也比S-APM-CBA更快。不同的最低電子未填滿能階所形成的電子陷阱對元件的表現並沒有明顯地影響。而trans-4-III是S-APM-CBA中的主要異構物，但是這個幾何構型剛好阻礙了電子的傳遞，進而使得S-APM-CBA表現比R-APM-CBA差。這個研究說明了分子在空間上的立體結構效應對元件的影響大於電子陷阱。 我們設計合成以PC61BM為基礎的碳六十衍生物PC61BPF。PC61BPF可以取代PC61BM，和P3HT形成的雙重混合系統P3HT:PC61BPF。也可以當作添加劑加入P3HT:PC61BM系統中，形成P3HT: PC61BM:PC61BPF三重混合系統。存在於五氟苯環和碳六十之間的超分子作用力可以有效地抑制碳六十衍生物的聚集。藉由加入8.3wt%的PC61BPF到主動層中，元件PC61BPF651的表現為3.88%，在加熱25小時之後，稍微下降至3.68%。當使用非五氟苯環的PC61BP，在相同的條件之下，元件的熱穩定性完全消失了。最重要的是，PC61BPF也可以用於低能隙的高分子系統。這個研究說明了利用超分子的作用力可以有效地控制薄膜的型態。最後，我們成功地利用碳六十衍生物來達成高效率且熱穩定的太陽能電池。

Functional fullerene materials are widely used in organic photovoltaics (OPVs), because fullerene has a lot of superior abilities, such as high electron mobility and suitable LUMO levels. A new class of fullerene bis-adducts based on diphenylmethano scaffolds were rationally designed and easily synthesized in the chapter 2. Compared to the LUMO level of PC61BM (−3.95 eV), the double functionalization effectively raises the LUMO levels of these fullerene materials to ca. −3.85 eV. The plane of the phenyl groups is preferentially parallel to the fullerene surface, leading to poor orbital interactions with C60 and negligible electronic effect. Importantly, such geometry sterically protects and shields the core C60 structure from severe intermolecular aggregation, rendering it intrinsically soluble, morphologically amorphous, and thermally stable. The device based on the P3HT:DMPCBA blend exhibited a Voc of 0.87 V, a Jsc of 9.05 mA/cm2, and an FF of 65.5%, leading to a PCE of 5.2%, Bis-adduct fullerenes surrounded by two insulating addends sterically attenuate intermolecular interaction and cause inferior electron transportation. In chapter 3, we have designed and synthesized a new class of bisadduct fullerene materials functionalized with two small phenylmethylmethano and thienylmethylmethano addends. The compact addends to promote fullerene intermolecular interactions result in aggregation-induced phase separation. The unfavorable morphologies can be optimized by incorporating a solvent additive. With the assistance of CN additive, the P3HT/MTC60BA-based device exhibited enhanced characteristics (a Voc of 0.78 V, a Jsc of 9.04 mA/cm2, and an FF of 69.8%), yielding a much higher PCE of 4.92%. More importantly, the additive-assisted morphological optimization is generally effective to all the four compact bis-adduct fullerenes. C60 bis-adduct containing a mixture of regioisomers with different LUMO energy evels and steric geometries could greatly affect the morphological and bulk properties. To investigate the regio-isomer effect on solar cell performance, in chapter 4 we have successfully designed and synthesized a bis-adduct (S-APM-CBA) by “tether-directed remote functionalization” strategy and a random bis-adduct (R-APM-CBA) by traditional cyclopropanation. Compared to the R-APM-CBA-based device, the device using S-APM-CBA yielded a much lower Jsc, FF, and PCE. Consistently, the S-AMP-CBA exhibited lower electron mobility than the R-AMP-CBA-based device. These results imply that the electronic shallow-trap effect ascribed to the LUMO energy variations turned out to be insignificant. The most probable trans-4-III isomer in S-AMP-CBA prevents the intermolecular facial contact of fullerenes, thereby hindering the electron transporting. This research demonstrated that steric effect of regio-isomers is more crucial than electronic shallow-trap effect. In chapter 5, a new PC61BM-based fullerene, PC61BPF is designed and synthesized. This new n-type material can replace PC61BM to form a P3HT:PC61BPF binary blend or serve as an additive to form a P3HT:PC61BM: PC61BPF ternary blend. Supramolecular attraction between the pentafluorophenyl group and the C60 can effectively suppress the PC61BPF/PC61BM materials from severe aggregation. By doping only 8.3 wt% PC61BPF, device PC61BPF651 exhibits a PCE of 3.88% and decreases slightly to 3.68% after heating for 25 h, preserving 95% of its original value. When PC61BP with non-fluorinated phenyl group is used to substitute PC61BPF, the stabilizing ability disappears completely. Most significantly, this strategy is demonstrated to be effective for a low band-gap polymer. These findings demonstrate that smart utilization of supramolecular interactions is an effective and practical strategy to control morphological evolution. In this thesis, we have successfully demonstrated a series of new fullerene derivatives to realize highly efficient and thermally stable solar cells.