利用三明治蒸鍍法製備平面異質接面型鈣鈦礦太陽能電池

Abstract

科技發展與人口數量激增的需求下，能源議題受到國際高度重視，各界積極投入 新型能源開發，例如風力發電或是太陽能發電。太陽能因具近乎無限之蘊含量、環境 友善與易取得性，使得太陽能電池成為具有潛力的候選人之一。在各類太陽能電池中， 鈣鈦礦太陽能電池轉換效率爬升速度之快，短短數年間，效率已超過 22%以上。脫胎 自染料敏化與高分子太陽能電池，簡單製程而生產成本低廉的特性使得各方研究團隊 紛紛投入，不僅光電轉換效率良好、大面積製備的潛力且更可拓展至軟性基板上，使 得此太陽能電池的應用領域更加廣泛。本研究著重於鈣鈦礦太陽能電池元件的製備， 提出三明治蒸鍍法並將其應用於自製蒸鍍腔體。不同於一般製備方式受到高限制製作 環境影響，此方式可在相對低溫低壓的環境需求下製作高效率有機鈣鈦礦薄膜太陽能 電池。 本實驗首先以溶液製程成長鈣鈦礦薄膜，但由於無法兼具足夠厚度與薄膜均勻覆 蓋性，後改以溶液輔助製程製作，進而可得覆蓋性和薄膜均勻度皆良好之鈣鈦礦薄膜。 再者提整適當的溶液覆蓋時間、塗佈轉速與適當的基板退火參數調整，可有效精準控 制 CH3NH3I 離子的擴散距離，優化鈣鈦礦結晶品質與晶粒大小，成功將轉換效率提升 至 10.91%。 但溶液輔助製程中，鈣鈦礦容易生成過快而導致結晶雜亂與電池表面產生不導電 物(CH3NH3I)之沉澱而影響電池表現與穩定性。因此提出三明治蒸鍍法(SDT)製備鈣鈦 礦薄膜， 利用 PbI2-CH3NH3I-PbI2 三明治結構雙向滲透(double interdiffusion)特性，以極 薄鈣鈦礦基準層誘導控制 CH3NH3I 粒子的擴散行為，並且調整蒸鍍溫度控制反應動能， 使反應具備足夠能量而連續且擴散長度充足地生成品質優良的鈣鈦礦薄膜。接著進一 步將溶液改良技巧引入蒸鍍製程，利用氣相微量溶液輔助法之快速分佈且均勻覆蓋特 性，避免旋塗時的濃度梯度問題，促使鈣鈦礦快速生成粒徑大小超過 1 μm 大小之薄膜 結晶並將效率一舉突破至 14.53%且沒有遲滯效應的產生。 為進一步提升光電流的表現，改使用載子擴散距離超過一微米之 CH3NH3PbI3- xClx 鈣鈦礦材料增加光吸收量，並發現於高真空度蒸鍍環境下有效提升反應的穩定性， 將效率提升至 14.77%。接著降低 PbCl2 蒸鍍速度與利用 PEDOT:PSS 參雜氧化鉬 (MoOx ) ，提升鈣鈦礦層中的平整度並且降低 Rs 阻值，再以旋塗方式沉積 BCP，提升 電洞阻擋層之效用，可將效率提升至 14.78%。最後，利用溶液輔助退火(solvent annealing)的技巧，利用 DMSO 營造適當之氣相濃度環境，使得 MAI 粒子再次移動達 到二次結晶，大幅優化結晶狀況與提升載子分離能力，最大鈣鈦礦結晶尺寸接近 3.5 μm， 光電流可達 20.94 mA/cm2， 效率為 15.17%具些微遲滯效應之鈣鈦礦太陽能電池。

Due to the fast growth of population and evolution of technology, the energy issue has received extensive attention worldwide, so the world makes significant efforts on developing alternative energy such as wind energy and solar energy. Solar energy exhibits inexhaustible, eco-friendly and easy accessible properties, making it one of the best candidates for next generation energy. Among all kinds of solar cells, the perovskite solar cells have achieved over 22% power conversion efficiency in only a few years, a significant progress compared with other solar cells. Adapted from the dye-sensitized solar cells and polymer solar cells, plenty of researchers have been attracted by the advantages of low-cost fabrication process with the high conversion efficiency. Perovskite not only exploits the potential of large-area cells but also opens up the field of flexible substrates. Therefore, this thesis focuses on the perovskite solar cells. In this research, the sandwich deposition technique (SDT) process was explored to fabricate the perovskite solar cell with the homemade chamber. Different from the normal procedure often equipped with high restricted condition, this approach can be conducted under the relatively low pressure and temperature environment, which truly enables the less demanding requirements for thin-film perovskite solar cells with high efficiency. First of all, the perovskite was deposited via the solution process first. However, both the uniform coverage and adequate thickness of thin film cannot be constructed simultaneously. To fix the problem, the PbI2 layer was deposited by the thermal evaporation which leads to the excellent coverage of perovskite films with great uniformity. The following modification focuses on the CH3NH3I-solution dipping time, spin-coating rate and post-annealing temperature. With the adequate parameters in the whole process, the precise control of reaction of CH3NH3I with PbI2 can optimize the perovskite film quality with larger grain size, which eventually raises the efficiency to 10.91%. However, rapid formation of perovskite readily leads to the small grain size and the precipitation of CH3NH3I on the surface, which has negative influences on the performance and stability of the cells. Hence, the SDT process was applied instead of the pervious solution assisted process. By taking the advantages of double interdiffusion equipped by the PbI2- CH3NH3I-PbI2 structure, the extremely thin seed perovskite layer formed by the PbI2 and CH3NH3I accurately controlled the diffusion of CH3NH3I. In addition, to achieve better crystal quality of perovskite, the heating temperature of CH3NH3I powder was tuned in 3-to-1 process to make the formation of perovskite continuously and completely. At last, modified from the solvent engineering, the vapor-phase solution assisted approach prevents the radial gradientproblem that often happened in traditional solution process. The perovskite can be merged exceeding 1 μm with the superiority of the fast and even distribution of the vaporized solution. The efficiency was boosted to 14.53% with hysteresis-free. Furthermore, in order to further promote the photocurrent density, the CH3NH3PbI3- xClx was selected for better light absorption by thicker thickness owing to the carrier diffusion length over 1 μm. The efficiency can be raised up to 14.77% with better stability under the condition of higher vacuum degree. Next, the poly(3,4-ethylenedioxythiophene)- poly(styrenesulfonate) (PEDOT:PSS) was doped with MoOx and the deposition rate of the PbCl2 was declined. After that, the bathocuproine (BCP) was deposited by the spin-coating instead of thermal evaporating. These three steps decrease the series resistance (Rs) and enhance the hole-blocking ability, yielding the efficiency of 14.78%. Moreover, the solvent annealing was introduced to the SDT process for optimizing the quality of CH3NH3PbI3-xClx. The usage of dimethyl sulfoxide (DMSO) creates a solvent-filled environment to accomplish the second diffusion of CH3NH3I, which effectively enhances the perovskite crystalline with larger grain size and carrier extracting ability. As the result, the average grain size of perovskite is 789.432 nm (the maximum grain size is close to 3.5 μm) and the photocurrent density reaches 20.94 mA/cm2, yielding the efficiency of 15.17% with only slight hysteresis phenomenon.