共軛添加劑對有機光伏太陽能電池之熱穩定性探討

Abstract

Part Ⅰ.具有末端官能基的共軛小分子添加劑 在這項工作中，我們準備了四個星形共軛小分子，三苯胺二噻吩（TBT）衍生物，即TBT-H，TBT-Br，TBT-OH和TBT-N3分別具有不同端基，氫化物，溴化物，羥基和疊氮化物末端官能基。這些TBT衍生物應用於有機光伏電池的活性層的添加劑，以研究分子間相互作用（TBT-H，TBT-OH）或交聯（TBT-N3，TBT-Br）對有機光伏的長期熱穩定性的影響設備。從混合膜形態，光電子和器件性能的分析，我們觀察到在加熱添加劑TBT-N3和TBT-Br的設備中在150°C的加速加熱測試期間的熱穩定性的顯著增強。這兩種添加劑作為交聯劑，並構造有效阻止熱促進的富勒烯的聚集，從而導致高度穩定的形態。當與相應的正常器件比較時，P3HT導入TBT-N3的元件表現出更大的穩定性。在150°C下144小時之後，光電轉換效率（PCE）仍能保持高達2.5％。由於這種增強，製造了基於非晶低帶隙聚合物PTB7添加了TBT-N3。我們觀察到器件穩定性的顯著改進，在150 °C加熱的加速實驗下，保持其初始PCE的約60％（從5.0％至3.3％）。相反，相應的正常器件的PCE衰減到其初始值的0.01％。 Part II. 可見光高穿透的共軛高分子 在本研究中，我們合成了兩種EMD高分子衍生物、分別為PBTEMD和PFEMD。這些EMD衍生物聚合物用作在聚合物太陽能電池的活性層中當作給體與PC71BM共混之共混膜，以研究它們的光電性能和其相關的光伏性能。據我們所知，這是第一個使用EMD衍生物應用於有機太陽能電池的研究。我們比較了其分子結構，相關的吸收、能階、熱性能和有機太陽能電池的熱穩定性。因為PEEMD的主吸收處於近紅外光譜（600nm至800nm）的範圍內。PFEMD的共混膜膜厚為95nm時其透明度高於80％，並且所構造的器件在AM 1.5G（100mW cm -2）下顯示最高2.5％的光電功率轉換效率。除此之外，我們觀察到交聯型添加劑（TBT-N3）的元件其熱穩定性有顯著提高。在150°C加熱的加速實驗下，仍能保持約60％的初始PCE。相反的其相對應的正常器件其PCE衰減到其初始值的0.01％，己微乎其微。

Part III. 添加多功能添加劑對有機光伏增強器件性能和穩定性的影響 在本研究中，我們開發了以二酮吡咯並吡咯（DPP）為核心的新型添加劑具有末端疊氮官能基團的烷基鏈以及不同推拉電子性與交聯官能基的共軛臂，分別命名為；DPPBTDA，DPPPDA和DPPTPTA。為了研究導入添加劑對光電效率與熱穩定性提升的影響，我們分別將DPPBTDA，DPPPDA和DPPTPTA摻入以商業化且具有高效率的有機導電高分子（PTB7-Th）作為供體和富勒烯衍生物（PC61BM）作為受體組成的活性層中。探討不同添加量的DPPBTDA、DPPPDA或DPPTPTA於倒置結構中的形貌變化與光電特性。在光伏性能方面，5 wt％DPPBTDA時展現了6.75 ％的功率轉換效率，而5％DPPPDA的OPV顯示7.35％的PCE。其中呈現最高光電轉換效率的為PTB7-Th：PC61BM與DPPTPTA為3 wt％時呈現高達8.11％的光電轉換效率，達到了20%的效率提升。於熱交聯反應的部分我們利用FT-IR和DSC進行分析，發現所設計的添加劑其反應溫度會受其熔點與結晶度所影響。由FT-IR的結果得知本研究所設計的三個添加劑皆能與PC61BM產生交聯反應。其加熱後的結晶現象也由光學顯微鏡（OM）的結果得以證實。加入交聯劑的活性層在150°C下加熱18小時後僅觀察到很少的富勒烯晶體，反觀未添加交聯劑的PTB7-Th:PC61BM共混膜在150°C下加熱6小時後便觀察到其共混膜產生大量的PCBM結晶。其OM所觀察到的現象與光電轉換效率相似，未導入添加劑的PTB7-Th:PC61BM共混膜於6小時後便不具光電轉換效率，再導入添加劑的部分，其中導入5 wt％的DPPTPTA 在150°C下加熱18小時後，功率轉換效率保持在4.02％。由電荷遷移率以及AFM的分析結果中得知階梯狀的能階能有效的提高光電轉換效率，且經交聯反應後能有效提高PTB7-Th:PC61BM共混膜的熱穩定性。

Part Ⅰ. Conjugated small molecule additives with terminal functional groups In this work, we prepared four star-shaped conjugated small molecules, the triphenylamine dithiophene (TBT) derivatives, namely TBT-H, TBT-Br, TBT-OH, and TBT-N3 presenting hydride, bromide, hydroxyl, and azide terminal functional groups, respectively. These TBT derivatives were used as additives in the active layers of organic photovoltaics to investigate the effect of intermolecular interactions (TBT-H, TBT-OH) or crosslinking (TBT-N3, TBT-Br) on the long-term thermal stability of the devices. From analyses of blend film morphologies, and optoelectronic and device performance, we observed significant enhancements in thermal stability during accelerated heating tests at 150 °C for the devices incorporated with the additives TBT-N3 and TBT-Br. These two additives functioned as crosslinkers, and constructed local borders that effectively impeded heat-promoted fullerene aggregation, thereby leading to highly stable morphologies. When compared with corresponding normal devices, the TBT-N3–derived devices based on poly(3-hexylthiophene) exhibited greater stability, with the power conversion efficiency (PCE) remaining as high as 2.5% after 144 h at 150 °C. Because of this enhancement, a device based on an amorphous low-bandgap polymer, namely poly(thieno[3,4-b]thiophene-alt-benzodithiophene), with the addition of TBT-N3 was fabricated. We observed a significant improvement in device stability, retaining approximately 60% (from 5.0 to 3.3%) of its initial PCE under accelerated heating (150 °C). In contrast, the PCE of the corresponding normal device decayed to 0.01% of its initial value. Part II. Visibly Transparent Low Bandgap Conjugated Polymers In this study, we synthesized two emeraldicene (EMD) based conjugated polymers, by polymerization with 4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole and (2-ethylhexyl) -9H-fluorene, namely PBTEMD and PFEMD, respectively. These EMD derivatives polymers were used as donor materials that blend with [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) in the active layers of polymer solar cells (PSCs) to investigate their optoelectronic properties and related photovoltaic performance. To best of our knowledge, this is the first study using EMD derivatives for PSC application. We compared their molecular structure, related absorption, energy levels, thermal properties and thermal stability for PSC application. The main absorption of PFEMD is in the range of near IR spectrum (600nm to 800nm). We obtained transparency of greater than 85% for the blend film of PFEMD and the constructed device exhibited the power conversion of 2.5 % under AM 1.5 G (100 mW cm−2). Apart from that, we observed a significant enhancement in thermal stability for the device incorporating an additive crosslinker (TBT-N3), which retaining approximately 60% of its initial PCE under accelerated heating (150 °C). In contrast, the PCE of the corresponding normal device decayed to 0.01% of its initial value. Part III. Enhancement Device Performance and Stability of Organic Photovoltaics via Incorporating Multifunctional additive A novel type of crosslinkers based on diketopyrrolopyrrole (DPP) as core, azide groups on the terminal of alkyl chains along with bithienyl, phenyl or terphenyl as conjugated arms (DPPBTDA, DPPPDA and DPPTPTA, accordingly) were developed. In order to investigate the enhancement of efficiency and thermal stability caused by crosslinkers, DPPBTDA, DPPPDA and DPPTPTA were respectively blend into the active layer which consists of a high performance conducting polymer (PTH7-Th) and a fullerene derivative (PC61BM). Inverted organic photovoltaics (OPVs) were fabricated by spin-coating the blends of PTB7-Th as donor, PC61BM as acceptor and different amounts of DPPBTDA, DPPPDA or DPPTPTA. In terms of photovoltaic performance, the OPV with 5% DPPBTDA showed the power conversion efficiency (PCE) of 6.75 % whereas the OPV with 5% DPPPDA showed a PCE of 7.35 %. Furthermore, a PCE of 8.11 % was observed for the PTB7-TH:PC61BM blending with 3 % DPPTPTA. On the other hand, the morphology of active layer has to be carefully controlled to offer optimum photovoltaic performances. According to FT-IR and UV-vis analysis, the crosslinking reaction did occur between the additives and PC61BM. The optical microscope (OM) result also indicates that only few fullerene crystals can be observed in the active layers with the crosslinkers upon heating the samples at 150˚C for 18 hours. Especially, the device with 5% DPPTPTA remained a power conversion efficiency of 4.02 % after heated at 150˚C for 18 h. Apart from that, the result of charge mobilities and atomic force microscope (AFM) showed ladder type energy level can be increase photovoltaics performance, and further enhance the thermal stability via crosslinking reactions.