利用超寬頻激發探測光譜研究奈米粒子提昇銅銦鎵硒薄膜太陽能電池之研究

Abstract

本研究利用超寬頻激發探測光譜研究奈米粒子提昇銅銦鎵硒薄膜太陽能電池之研究。一個是利用金屬奈米粒子的的特性─表面電漿共振(Surface Plasmon Resonance)，另一個則是利用硒化鎘量子點的光子向下轉換(photon down-conversion)機制，達成銅銦鎵硒薄膜太陽能電池的效率提升。 在這個實驗中，我們將金奈米粒子置於銅銦鎵硒薄膜上，並研究其薄膜表面的超快載流子動力學。通過超寬激發 - 探測光譜分析，證實由表面電漿效應的物理機制，使得表面電漿-銅銦鎵硒薄膜具有強的光轉換能力，並且我們也由理論計算與我們的實驗相對應，表面電漿效應確實強化了電子電洞對的產生。而在硒化鎘量子點銅銦鎵硒太陽能電池，由外部量子效率觀察，證實效率由光子向下轉換機制得到提升，這一結果表明金奈米顆粒與奈米晶粒的摻入，是一個具潛力的方法來強化銅銦鎵硒太陽能電池的光轉換效率。

In this study, we have employed the ultrabroadband pump-probe spectroscopy to investigate the enhancement of efficiency in CIGS thin film solar cells via nanoparticles. Using the plasmonic effect of gold nano-partilce is an approach to improve the efficiency of CIGS solar cells. Another way is utilizing the down-shifting effect of CdSe quantum dots to enhance the photocurrent. We have performed the ultrabroadband femtosecond pump-probe spectroscopy of CuIn1-xGaxSe2 (CIGS) thin films with and without Au nanoparticles (NPs) incorporation， and elaborately analyzed the lifetimes and zero momentum for the hot carrier relaxation. The signals of enhanced photobleach (PB) and waned photoinduced absorption (PIA) attributed to surface plasmon resonance (SPR) of Au NPs were observed in the transient differential absorption spectrum. This result has suggested the carriers can be considerably excited from ground state to lower energy level. The improvements of electrical transport by suppressing the surface recombination of photoinduced carriers via enhanced local electromagnetic field (LEMF) was also confirmed by extracted hot carrier lifetime and calculated electromagnetic field distribution. Finally， the theoretical calculation for resonant energy transfer (RET)-induced enhancement in probability of exciting electron-hole pairs was conducted and the result is well corresponding to the enhanced PB peak of transient differential absorption in plasmonic CIGS. In CdSe quantum dots CIGS solar cells was observed by an external quantum efficiency， we confirmed the success of the photon down conversion mechanism to enhance optical conversion efficiency. These result has suggested that Surface Plasma Resonance and photon down-conversion mechanism are viable approachs to boosting high-efficiency CIGS solar cells.