製備及結構鑑定有機太陽能電池

Fabrication and Structural Characterization of Organic Based Solar Cells

張峻瑜(Chun-Yu Chang)

指導教授 ： 林唯芳

國立臺灣大學/工學院/材料科學與工程學研究所/博士(2017年)

https://doi.org/10.6342/NTU201701197

摘要

平面異質接面鈣鈦礦太陽能電池由於可溶液製程製備，故為相當具有前景的低成本再生能源。控制鈣鈦礦層的結晶行為及形貌對於元件的光電轉換效率表現具有相當大的影響。在本論文第一項研究中，我們將氯化鉛及甲基碘化胺溶於二甲基甲醯胺中以得到鈣鈦礦前驅物溶液。我們將此溶液滴在事先預熱的基材上，並以即時低掠角入射廣角X光散射技術分析其自溶液態轉換至最終結晶薄膜之形成機制。基材預熱溫度範圍為70oC至180oC。研究發現，當基材溫度低於100oC，鈣鈦礦薄膜的形成機制主要可分為三個階段:初始溶液階段、固液薄膜過渡階段以及中間產物轉換至結晶鈣鈦礦階段。在此三階段中，不同的相轉換路徑會同時進行。當基材溫度提升到介於100oC至180oC時，鈣鈦礦薄膜的形成機制將由”多階段形成機制”轉變為”直接形成機制”。此部分的研究結果將可讓我們了解如何設計與製備高效率鈣鈦礦太陽能電池。
了解鈣鈦礦薄膜的形成機制後，在本論文的第二項研究中，我們將高分子添加劑加入至鈣鈦礦前驅物溶液中以製備平面異質接面鈣鈦礦太陽能電池，並將整個元件的製備溫度被控制在150oC以下。當加入1 wt%的聚乙二醇時，元件的光電轉換效率由未加入添加劑時10.58% 提升至13.20%，相當於提升了25個百分點。我們利用SEM, XRD和AFM等技術去觀察鈣鈦礦薄膜在加入添加劑後其形貌的變化。研究結果發現，高分子優異之成膜特性有助於控制鈣鈦礦晶體的聚集與成長，因而可形成均勻且平坦的薄膜。然而聚乙二醇的絕緣特性限制了添加劑在鈣鈦礦層中的含量。在最佳化的比例下，元件的開路電壓與短路電流均有大幅度地提升。
除了鈣鈦礦太陽能電池之外，我們亦利用低結晶性的P3TI及高結晶性的P6TI異靛藍素基予體-受體交替共聚高分子分別與PC71BM混摻，製備塊材異質接面高分子太陽能電。藉由加入添加劑以控制奈米尺度相分離形貌，可得到良好的光電轉換效率。對於P3TI:PC71BM系統而言，無論選用何種添加劑，元件均有相似的效率提升。然而P6TI:PC71BM系統卻會因添加劑的種類為脂肪族或芳香族而影響元件效率。為了進一步了解高分子的結晶性與添加劑的種類對於塊材異質接面薄膜奈米形貌的影響，在本論文的第三項研究中，我們利用低掠角入射小角及廣角X光散射技術去做定量的分析。結果發現，PC71BM分子可藉由添加劑的幫助輕易地進入P3TI高分子區域。無論使用的添加劑為脂肪族的1,8二碘辛烷或是芳香族的1-氯萘，均可使PC71BM分子團由未加入添加劑時的24奈米縮小至加入添加劑時的5奈米。另一方面，PC71BM分子因難以進入高結晶性P6TI高分子結晶區域，故傾向於自聚集，導致在未加入添加劑時PC71BM分子團相對較大，為58奈米。而脂肪族的1,8二碘辛烷與芳香族的1-氯萘添加劑可使PC71BM分子團分別縮小至7奈米與13奈米。結晶的P6TI區域會影響添加劑與PC71BM分子團的交互作用，使PC71BM分子團的與P6TI高分子結晶區域大小相近，形成連續網狀通路而利於電荷的傳輸。有別於一般常見的低結晶性予體-受體交替共聚高分子，此研究提供高分子的結晶效應對於添加劑種類的選擇以及塊材異質接面薄膜奈米形貌的影響，對於開發高效率高分子太陽能電池極為重要。

關鍵字

有機太陽能電池 ； 形貌 ； X光散射技術 ； 結晶動力學 ； 高分子添加劑 ； 異靛藍素

並列摘要

Solution processable planar heterojunction perovskite solar cell is a very promising new technology for low cost renewable energy. Controlling the crystallization and morphology of perovskite film is crucial for the fabrication of high efficiency perovskite solar cells. In the first research work, we investigated the formation mechanism of the drop-cast perovskite film from its precursor solution, PbCl2 and CH3NH3I in N,N-dimethylformamide, to crystalline CH3NH3PbI3-xClx film at different substrate temperature from 70oC to 180oC. We employed in-situ grazing-incidence wide-angle X-ray scattering (GIWAXS) technique for the study. When the substrate temperature is at or below 100°C, the perovskite film is formed in three stages: initial solution stage, transition to solid film stage, and the transformation stage for intermediates into crystalline perovskite film. In each stage, the multiple routes for phase transformations proceed concurrently. However, when the substrate temperature is increased from 100oC to 180oC, the formation mechanism of perovskite film is changed from the “multi-stage formations mechanism” to the “direct formation mechanism”. The result of this study provides useful knowledge to design and fabricate crystalline perovskite film for high efficiency solar cell.
By knowing the formation mechanism of perovskite film, in the second research work, we fabricated the planar heterojunction perovskite solar cell by using polymer additive in perovskite precursor solution. A 25% increase in power conversion efficiency at a value of 13.2% is achieved by adding 1wt% of poly(ethylene glycol) in the perovskite layer using 150oC processed TiO2 nanoparticle layer. The morphology of this new perovskite was carefully studied by SEM, XRD and AFM. The results reveal that the additive controls the size and aggregation of perovskite crystals and helps the formation of smooth film over TiO2 completely. Thus, the Voc and Jsc are greatly increased to have a high efficiency solar cell. The amount of additive is optimized at 1 wt% due to its insulating characteristics. This research provides a facile way to fabricate high efficiency perovskite solar cell by low temperature solution process (<150oC), which has the advancement of conserving energy over the traditional high temperature sintering TiO2 compact layer device.
In addition to the perovskite solar cells, high power conversion efficiency of bulk heterojunction (BHJ) polymer solar cell can be fabricated from either low crystallinity (P3TI) or high crystallinity (P6TI) of isoindigo-based donor-acceptor alternating copolymers blended with PC71BM by controlling nanophase separation using additive. The P3TI shows similar device performance regardless the type of additives, while the P6TI is significantly affected by the additive being aliphatic or aromatic. To understand the interplays of crystallinity of polymer and type of additive on the formation of nanomorphology of BHJ, in the third research work, we employed the simultaneous GISAXS and GIWAXS technique to do the quantitative investigation of nanomorphology. By incorporating additive, the PC71BM molecules can be easily intercalated into the P3TI polymer-rich domain and the size of PC71BM clusters is reduced from about 24 nm to about 5 nm by either aliphatic 1,8-diiodooctane (DIO) or aromatic 1-chloronaphthalene (CN). By comparison, the PC71BM molecules are more difficult to be intercalated into high crystalline P6TI dense domain and the PC71BM molecules have higher tendency to be self-aggregated which result in a larger size of PC71BM clusters about 58 nm. The clusters can be reduced to about 7 nm by DIO and 13 nm by CN. The presence of crystallites in P6TI domain can interact with the additive to tailor the crystallization of PC71BM clusters to be in the similar size with P6TI crystallites and form the connected network for efficient charge transportation. This is a new finding phenomenon of crystallinity effect which does not observe in the common low crystalline donor-acceptor alternating copolymers such as PTB7. The results provide a useful guideline to manipulate the desired morphology of BHJ film constructed from alternating copolymer with different crystallinity, which is critical for achieving high power conversion efficiency of solar cells.

並列關鍵字

organic based solar cells ； morphology ； X-ray scattering ； crystallization kinetics ； polymer additive ； isoindigo

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