鈣鈦礦太陽能電池添加硫化鉛奈米粒子之結晶機制之研究

The Mechanism of Addition of PbS Nanocrystals to Promote Nucleation of Organic-Inorganic Hybrid Perovskite Solar Cells

蕭妤芸(Yu-Yun Hsiao)

指導教授 ： 陳俊維

國立臺灣大學/工學院/材料科學與工程學研究所/碩士(2017年)

https://doi.org/10.6342/NTU201702208

摘要

本研究將表面配有I-的硫化鉛奈米晶體(PbS/I-)混入PbCl2與CH3NH3I的DMF溶液中形成前驅溶液，藉由 PbS/I-的添加來改變鈣鈦礦的結晶行為並進一步探討其結晶機制。添加硫化鉛奈米晶體的鈣鈦礦薄膜，可以得到較佳的表面形貌及更好的元件表現。利用in-situ GIWAXS觀察其結晶的過程變化，低掠角的X光散射(Grazing-incidence wide angle x-ray scattering GIWAXS)搭配平面接收器，可以得知薄膜內晶體排列之方向，更進一步以動力學的角度去計算其活化能。我們發現0wt%PbS之CH3NH3PbI3-xClx薄膜(Pristine)在110℃退火下，從前驅溶液旋鍍到基材上形成薄膜之過程相的變化可分三個階段：第一階段為鈣鈦礦結晶相生成且中間相生成並迅速成長、第二階段為中間相強度不變但鈣鈦礦相迅速成長、第三階段為中間相迅速消失且鈣鈦礦結晶生長到最大結晶強度；而在1wt%PbS之CH3NH3PbI3-xClx薄膜不較不同的是第一階段鈣鈦礦結晶相迅速成長而中間相生成速度慢且強度低、第二階段中間相強度增強但沒持續生成的趨勢、第三階段鈣鈦礦結晶相穩定且中間相消失。在GIWAXS的量測中顯示，經過退火後形成鈣鈦礦的薄膜時，添加硫化鉛奈米粒子的CH3NH3PbI3-xClx薄膜(1wt% PbS)中，完全只有Perovskite之繞射峰，相較之下0wt%PbS之CH3NH3PbI3-xClx薄膜(Pristine)仍有PbI2之結晶相，此為部分鈣鈦礦未完全轉換成CH3NH3PbI3-xClx ，降解成PbI2，因此添加硫化鉛奈米晶體能幫助鈣鈦礦在結晶之過程中將相轉換更完全。在二維繞射圖的結果可得知，在PbS/I-占固體總重0wt%的薄膜其分佈之方向部分之晶粒集中於90°但整體方向分佈較平均，而PbS/I-占固體總重1wt%的薄膜其分佈之方向大部分集中於90°且在90°相對強度分佈將近PbS/I-占固體總重0wt%的薄膜之1.5倍。因此添加硫化鉛奈米晶體會使在形成鈣鈦礦結晶之過程晶粒成長之方向較一致性且大多集中於垂直基板之方向。在活化能分析方面，PbS/I-占固體總0wt%之鈣鈦礦薄膜鈣鈦礦相之結晶活化能184kJ/mol；而PbS/I-占固體總1wt%之鈣鈦礦薄膜鈣鈦礦相之結晶活化能約為57 kJ/mol。根據我們的研究結果，在鈣鈦礦的前驅溶液中混入硫化鉛奈米晶體會使其更易形成鈣鈦礦結晶相，且在薄膜的生長方向會垂直於 基板方向更有利於載子的傳輸，此外，還能降低形成鈣鈦礦的活化能，使其更易形成鈣鈦礦結晶相，因此藉由硫化鉛奈米晶體的添加，我們可以製作出高效能的太陽能電池。

關鍵字

鈣鈦礦 ； 結晶機制 ； 硫化鉛奈米晶體 ； 生長方向 ； 活化能

並列摘要

This work, we use inorganic nanocrystals of PbS/I- as additive and nucleus to improve thin film morphology and discuss it nucleation mechanism. A small amount of dispersed PbS nanocrystals which were covered with Perovskite precursor molecules of methylammonium iodide (CH3NH3I, MAI) through the ligand-seed like nucleation sites to promote the formation of Perovskite lattice structure. To realize inorganic nanocrystals of PbS/I- as additive in the Perovskite precursor how to transform the Perovskite thin film, we employed an in-situ grazing-incidence wide-angle X-ray scattering (GIWAXS) technique for this study. In the precursor without PbS/I-, When the substrate temperature is at 110℃ the Perovskite film is formed in three stage: the first stage increase rapid speed intermediate phase and Perovskite phase appear; the second stage the Perovskite phase growth fast speed; the final stage intermediate phase disappear and Perovskite intensity reach maximum. However, in the precursor with PbS/I-, the first stage Perovskite phase increase rapid speed and intermediate phase intensity very low; the second stage Perovskite phase intensity reach maximum; the final stage the intermediate phase rapid disappear and Perovskite phase remain stable. Moreover, in the 2D-GIWAXS pattern shows that Perovskite phase (110) orientation growth is the vertical direction for the sample deposited with 1wt% MAI capped PbS nanocrystals. And last but not least, without PbS/I- perovskite thin film activation energy is 184KJ/mol; with PbS/I- Perovskite thin film activation energy is 57KJ/mol. The result of this study shows that intermixing PbS nanocrystals in Perovskite precursor solution, such as faster Perovskite crystallization kinetics and lower activation energy, increase crystal domain, enhanced coverage and uniformity. It provides useful technique to improve Perovskite solar cell performance.

並列關鍵字

Crystallization kinetics ； Formation mechanism ； Orientation ； Activation energy ； Grazing-incidence wide angle X-ray scattering(GIWAXS) ； Perovskite ； PbS nanocrystals ； Solar cell

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