水溶性碲化鎘量子點之製備與其在太陽能電池之應用

Abstract

在化石燃料之過度使用下，地球大氣層二氧化碳濃度逐年增加，造成嚴重的「溫室效應」，促使地球總體溫度異常上升。近年來由於環保意識抬頭，人們警覺這問題的嚴重性，故積極地研發潔淨再生能源以取代傳統的化石燃料發電，減輕傳統發電方式所產生的污染。其中，太陽能可說是取之不盡、用之不竭，如果能有效的運用，將可降低環境負擔及紓解能源需求。 本研究探討水溶性CdTe量子點之製備與其在太陽能電池上之應用，水溶性量子點製備，係使用三種不同含鎘前驅物，利用3-巰基丙酸做為包覆劑。在固定的Cd/Te莫耳數比、相同的酸鹼值、相同反應溫度下，控制反應時間的長短，以合成粒徑不同的量子點，並藉由紫外/可見光光譜與螢光光譜對所合成量子點進行分析與發光特性鑑定，可估算粒徑大小與量子效率；再利用X光繞射及穿透式電子顯微鏡測定量子點之晶相及晶粒大小，實驗結果顯示綠光至紅光水溶性CdTe量子點粒徑大小為2~4 nm。 另一方面，為了降地成本提高太陽能電池光電轉換效率，本研究將所合成CdTe量子點與漿料混合，並利用網印技術均勻地塗佈在矽晶片上，再進行太陽電池模組效率量測，其主要原理係以CdTe量子點為吸光層，將短波長太陽光轉換成長波長的可見光，以提升光電轉換效率。我們亦探討摻雜[6,6]苯基C61丁酸甲酯( PCBM )改善載子傳輸，搭配不同的混合濃度與粒徑大小量子點對太陽能電池轉換效率的影響。

Global warming has been recognized as a consequence due to the tremendous increase in CO2 concentration in the earth atmosphere, which is caused by overconsumption of fossil fuels. Recently, the researches on renewable green energy to replace traditional fossil fuels have been actively persued to reduce environmental pollution and “green house effect”. Among all energy resources available, solar energy is undoubtedly one of the most sustainable and clean, which can effectively reduce the environmental loading and ease the energy crisis. This research is attempted to investigate the preparation of water-soluble CdTe QDs and their application in photovoltaic devices. The CdTe QDs capped with 3-mercaptopropionic acid (MPA) were synthesized from three different precursors containing Cd2+. With fixed Cd/Te molar ratio, pH value and reaction temperature, the CdTe QDs with a variety of sizes or emission wavelengths can be synthesized by controlling the reaction duration. The as-synthesized MPA-capped CdTe QDs were found to crystallize in both cubic and hexagonal structure by using X-ray diffraction and the size of nanocrystal sizes was determined to be 2-4 nm (corresponding to green to red emission) based on TEM microscopy. Furthermore, the determination of quantum yield (QY) of MPA-capped CdTe QDs have been carried out and found to be 37-65% based on the UV-Vis and photoluminescence (PL) spectral data. On the other hand, to cost down and to improve the conversion efficiency of photovoltaic (PV) devices, a mixture of CdTe QDs and sizing was prepared and daubed on the polycrystalline silicon wafer evenly by using screen-printing technique and the efficiency of photovoltaic devices was then measured with a solar simulator. By using CdTe QDs as the light-absorbing material, the short-wavelength UV can be converted into visible light and reused by the photovoltaic devices. We have also investigate the effect of adding [6,6] phenyl C61butyric acid methyl ether (PCBM) as an electron transport material in various contents with CdTe QDs on the improvement of solar conversion efficiency of the PV devices.