"以分子層沉積之聚(3,4-乙烯基二氧噻吩)作為鈣鈦礦電池內電洞傳輸層研究"

Abstract

本研究探討了使用(3,4-乙烯基二氧噻吩)和五氯化銻作為前驅物，藉由分子層沉積技術生長聚(3,4-乙烯基二氧噻吩)薄膜，在不同製程條件下和後處理過後的成長特徵、性質和製造出來的鈣鈦礦太陽能元件效率，在前驅物通入後加入一段暴露時間可以大大加速聚(3,4-乙烯基二氧噻吩)成核以及提升反應物濃度，使得每週期成長速率達6倍，但同時過量吸附的反應物也會阻礙新進聚(3,4-乙烯基二氧噻吩)分子的規整排列，並導致低結晶度和低導電度，另一方面，使用分段通入(3,4-乙烯基二氧噻吩)的方法可以同時增加成核速率、結晶度和導電度，這是因為此製程在增加反應物濃度的同時也能更徹底的移除殘餘物，也降低了聚(3,4-乙烯基二氧噻吩)薄膜內的摻雜程度，和標準製程相比，聚(3,4-乙烯基二氧噻吩)藉由分段通入(3,4-乙烯基二氧噻吩)的方式生長可以增加導電度和降低載子濃度，顯示出該製程的使用能夠使載子遷移率增加。在作為電洞傳輸層的效率表現上，而且使用分段通入(3,4-乙烯基二氧噻吩)製程生長的聚 (3,4-乙烯基二氧噻吩)做成的太陽能元件具有比起其他製程還要優異的光電轉換效率，然而，分子層沉積反應所殘留下來的含氯物質使得元件效率表現不佳。溶液及逆滲透水清洗、大氣下退火、真空下退火及真空下退火加上氧電漿等後處理被用來移除殘留的含氯物質，最後發現室溫下的真空退火加上氧電漿處理能夠得到最佳的平均光電效率11.0% (冠軍12.0%)，後處理之後效率的改善可以歸功於溫和的室溫真空退火條件能夠在去除含氯物質的同時較好地保留薄膜的載子傳輸性質，隨後的氧電漿處理則改善了表面沾濕並增進鈣鈦礦層的結晶度。

This study investigated the growth characteristics, properties, and hole-transporting performance in photovoltaic devices of poly(3,4-ethylenedioxythiophene) (PEDOT) thin films fabricated by molecular layer deposition (MLD)—using ethylenedioxythiophene (EDOT) and antimony pentachloride (SbCl5) as precursors—with varying processing and post-treatment conditions. Addition of precursor exposure steps to the MLD cycle significantly sped up nucleation of the PEDOT film and increased the growth per cycle (GPC) by ~6 folds owing to its increased reactant concentrations at the substrate surface, but the excessively adsorbed reactants also hindered ordering of the nascent PEDOT molecules, resulting in lower crystallinity and electrical conductivity. Use of discreet feeding in the MLD cycle, on the other hand, enhanced nucleation and GPC while also improved crystallinity and electrical conductivity of the PEDOT film, thanks to its combination of increased reactant concentrations and more thorough removal of excessive reactants, the latter of which led to reduced doping levels in the PEDOT film. The increased electrical conductivity and reduced doping levels observed with the discreet-feeding-deposited PEDOT film indicated increased hole mobility of the film. In terms of performance as a hole-transporting layer (HTL) in perovskite solar cell (PSC) devices, the discreet-feeding-deposited PEDOT film was superior to those deposited with the other processing conditions, but its resultant device performance was still dismal due to its residual chlorine content left by the MLD chemistry. Several post-treatment methods for reducing the residual chlorine content including rinsing with aqueous acid solutions or water, annealing in atmospheric pressure, annealing in vacuum with or without oxygen plasma, were tested, of which room-temperature annealing in vacuum coupled with a brief finish with oxygen plasma yielded the best PSC device performance: average power conversion efficiency of 11.0% (12.0% champion). The improvement in PSC device performance was attributed to better-preserved film quality from the mild room-temperature vacuum annealing condition, and to increased affinity of the PEDOT surface to the perovskite active layer upon the oxygen plasma treatment, which enhanced the crystallinity of the resultant perovskite layer.