有機金屬鹵化物鈣鈦礦太陽能電池之高效電洞傳輸層的開發

Abstract

為因應地球暖化及能源需求增加等問題，太陽能源的開發與利用越來越迫切與急需，本篇論文著重在鈣鈦礦太陽能電池開發及介面傳導層的機制探討。首先我們利用具相同HOMO值的電洞傳導材料，研究在相同能帶下其結構對載子轉移效率的影響，發現除電洞傳導層材料本身的電洞遷移率外，結晶性及介面之間的作用佔有更大的影響，藉由螢光光譜儀及阻抗分析儀，我們發現低平面性、具三苯胺側鍊的高分子結構，更能有效提升介面的載子轉移能力，並降低介面之間的載子複合現象，且我們發現缺陷密度與遲滯現象密切相關，在本研究中我們開發出此具有三苯胺側鍊結構且免摻雜的電洞傳導材料，藉由阻抗分析儀及缺陷密度分析來探討電洞傳導層對元件界面的影響。 此外為提升鈣鈦礦太陽能電池商用化的可行性，我們開發一種便宜且能大面積自組裝成長於導電基板的電洞傳導層，應用在反式結構的鈣鈦礦太陽能電池，避免了順式結構中常見的遲滯現象，其-COOH官能基使其能吸附於金屬表面，藉由光譜吸收儀及厚度的量測，可得到近乎是單分子厚度的有機薄膜，大大降低電洞傳導層在反式結構中可能產生的寄生吸光現象，並提高材料能隙使其具有更好的電子阻擋能力及更匹配的HOMO能帶。另外我們發現除了效率提升到19.05%，元件的製程良率及穩定性也因為此方法而改善，對於商用化鈣鈦礦太陽能電池來說，此研究極具參考價值。 接著，為了進一步改善鈣鈦礦太陽能電池的製程限制，我們放棄傳統的旋轉塗布製程，用浸泡塗布法在自組裝的電洞傳導層上塗布鈣鈦礦吸光 薄膜，目前最高光電轉換效率可達 14.6%，此方法不需要使用複雜的溶劑工法，並且可以大面積同時塗布，將可大幅降低太陽能電池的成本，其元素置換及溶劑選擇將會是未來的研究發展方向。

The global warming and the increasing demand of energy, causing in development and utilization of solar energy become urgent and necessary. In this dissertation, we focus on developing the new fabrication method of perovskite solar cells (PSCs) and carrier transport mechanism of the cell. Firstly, we demonstrate the different hole extraction layers (HELs) with similar highest-occupied-molecular-orbit (HOMO) level and study how carrier extraction ability is affected by chemical structures. We observe when HELs possess the same energy band, interface interaction between HELs and perovskite and crystallinity are more important than mobility. The photoluminescence and impedance studies show that polymer with triphenylamine side chain can more efficiently extract carriers from perovskite layers. Carrier interface recombination which is detrimental to carrier extraction has also been improved via side chain engineering. In this study, we find hysteresis phenomenon is strongly bound with trap density. We design a dopant-free conjugated polymer with triphenylamine side chain which can be utilized as a HEL in PSC and study the relation between hysteresis and device trap density. Next, to further speed the pace of commercializing the PSCs, we develop a novel method to deposit HELs on substrate to fabricate inverted structure (P-I-N structure)without hysteresis phenomenon. With the carboxylic group on side chain, the polyelectrolyte P3HT-COOH can self-assemble to metal cations and form a thin layer on ITO glass. It is material saving and it presents the possibility of large area fabrication in PSCs. The results of UV-visible absorption and thickness measurements tell us that it forms ultimate thin layer which avoids the parasitic light absorption in inverted PSCs. This method enlarges the optical bandgap with higher LUMO and lower HOMO, and it improves the PCE to 19.05%. Besides, device reproducibility and long-term stability are also improved. For commercializing the PSCs, this research has a certain reference value. Later, in order to improve the fabrication methods in PSCs, we change the traditional spin-coating method to deposit CH3NH3PbI3 layer. We propose dip coating method to fabricate solar devices. This method gets rid of complicated solvent engineering technique and is possible to deposit perovskite layer in large area devices. Element compositions and solvent replacement are solutions to further improve this method. The PCE of champion device has achieved 14.6%.