石墨烯添加劑對於有機-無機混成鈣鈦礦光伏元件特性 影響之研究

Abstract

本研究將單層、低氧化度石墨烯奈米片(graphene nanosheets，或簡稱 GNS)以溶液分散法方式摻混於有機無機混成鈣鈦礦之前驅物溶液中，以提升有機無機混成鈣鈦礦太陽能電池(organic-inorganic hybridperovskite solar cells，簡稱 PSCs)元件之效能。本研究分成三個部分：(1) GNS 之分散溶劑選擇與其分散特性分析、(2) 可分散 GNS 之鈣鈦礦溶液配方研究、(3) 摻混 GNS 之 PSC 元件特性研究。因 GNS 之易團聚特性，其於溶劑中若欲達均勻分散，則須採用高親和力之溶劑並搭配高能量混合方法。本研究經溶解度參數比對，並考量鈣鈦礦前驅物之可用溶劑後，選取 N-甲基吡咯烷酮 (1-Methyl-2-pyrrolidone，或簡稱 NMP)與二甲基亞碸(dimethyl sulfoxide，或簡稱 DMSO )並搭配高功率超音波破碎法進行 GNS 分散特性分析，結果發現 GNS 於 NMP 中之分散性遠優於 DMSO，可分別達到低於0.001 mg/ml 與 0.053 mg/ml 之穩定分散濃度，而 GNS 於上清液中之平均片徑仍可保持於 121.80 nm。根據此結果，本研究測試不同比例之 NMP 與 DMSO 添加於DMF 中所調製之鈣鈦礦前驅物溶液，評估其所製備 PSC 元件效能，結果發現各比例之溶液，經成膜條件最佳化後，均可產出效能良好之元件，而 NMP 之添加可顯著提升元件之 fill factor，推測為 NMP 與鈣鈦礦前驅物之配位傾向改善了鈣鈦礦薄膜之緻密度與覆蓋性所致。在摻混 GNS 之 PSC 元件特性方面，當採用上述可同時分散 GNS 並達到良好元件效能之溶液系統時，摻混 GNS 可提升元件效率與穩定度，於最佳之 3×10-4vol% GNS 摻混濃度下，元件效率達 16.12%，並可在相對濕度65-70%之大氣環境中存放超過 150 小時，仍維持初始效率的 80%以上。此改善效果經 X 光繞射儀與光致發光光譜儀分析，推測為 GNS 鈍化鈣鈦礦晶界中之缺陷，並以其疏水特性防止鈣鈦礦薄膜受水氣劣化所致。

This work studied mixing monolayer, low-oxidation graphene nanosheets (GNS) into the organic-inorganic hybrid perovskite precursor solution by solution dispersion method to enhance the performance of organic-inorganic hybrid perovskite solar cells (PSCs). This work was divided into three parts:(1) Selection of solvent for graphene dispersion and analysis of graphene dispersion characteristics, (2) Formulation of perovskite solution with the ability to disperse graphene, and (3) Characterization of perovskite layers with graphene and PSCs.Due to the easy agglomeration characteristics of GNS in solvent, it is necessary to select high-affinity solvent and use high-energy mixing method in order to disperse GNS uniformly. In this work, after understanding the solubility and considering the available solvents that can be used as perovskite precursors, 1-Methyl-2-pyrrolidone (NMP) and dimethyl sulfoxide (DMSO) were selected, and combined with high-power ultrasonic exfoliation, the dispersibility of GNS was analyzed. The results found that the dispersibility of GNS in NMP is much better than that of DMSO, and stable dispersion concentrations of less than 0.001 mg/ml and 0.053 mg/ml were achieved, respectively. The average flake diameter of GNS in the supernatant was still maintained at 121.80 nm. Base on this result, this work tested the perovskite precursor solutions with different ratios of NMP and DMSO into DMF to evaluate the performance of the prepared PSC devices.After optimizing the film forming conditions, it was found that the formulations with NMP all were able to fabricate devices with good performance, and that the addition of NMP can significantly improve the fill factor of the devices, which is speculated that the coordination tendency between NMP and perovskite precursors improves the density and coverage of perovskite films. In terms of the characteristics of PSCs mixed with GNS, GNS was able to improve the efficiency and stability of the devices. When the concentration of GNS reached 3×10-4vol% in PSCs, the PCE of champion device reached a value of 16.12%, and maintained more than 80% of its initial PCE after 150 hours in an atmospheric environment with a relative humidity of 65-70%. The improvement effect was analyzed by X-ray diffractometer and photoluminescence spectrometer, and it was speculated that GNS passivated the defects in the perovskite grain boundaries. Additionally, the hydrophobic property of GNS prevented the perovskite film from being degraded by moisture.