利用超寬頻激發探測光譜研究P3HT:PCBM太陽能電池之載子超快動力學

Abstract

本論文利用自行架設的NOPA( non-collinear optical parametric amplifier，非共線光參數放大器)系統研究太陽能電池中有機高分子聚合物/富勒烯複合物的(聚(3-己烷噻吩) (P3HT) / [ 6,6 ]苯基C61丁酸甲酯 (PCBM))的載子超快動力學。透過NOPA系統所產生的小於10飛秒脈衝及多頻道鎖相放大器(multichannel lock-in amplifier)可將各波段(520~700 nm)所偵測到的超快動態反應清晰完整的紀錄。此高頻率、高時間解析的雷射系統非常適合用來探測光化學反應裡中間物質的產生過程以及分子結構的動態變化情形。 近年來P3HT:PCBM太陽能電池因為其低毒性、價格低廉、製作容易、可調的電子能帶結構和機械性能而廣泛地受到重視。但是P3HT和PCBM的比例、退火方式、薄膜厚度等因素都會影響太陽能電池的光電轉換效率，然而其中的原因目前仍不甚明朗。本論文利用時間解析激發探測光譜研究P3HT:PCBM薄膜、P3HT薄膜以及前退火、後退火的P3HT:PCBM元件中光激載子之超快動態行為，並建構出其載子動力學模型，以釐清因製程技術對光電轉換效率的影響，期望有助於太陽能電池技術的發展。

In this thesis, a homemade NOPA (non-collinear optical parametric amplifier) system was used to study the ultrafast dynamics of solar cell of poly(3-hexylthiophene) (P3HT):[6,6]-phenyl-C61-butyric acid methyl ester (PCBM). The sub-10 fs laser pulses with a broad spectrum in visible range are frequently used to study the ultrafast dynamics of photochemical reaction and transient molecular structure changes. Recently, P3HT:PCBM solar cell attracted a great deal of attention due to the low toxicity, low price, simple fabrication processes, adjustable electronic band structure and mechanical properties. However, the ratio between P3HT and PCBM, the annealing method, and the thin film thickness seriously affect the photoelectric conversion efficiency. Here, the ultrabroadband pump-probe spectroscopy was used to study the ultrafast dynamics of P3HT:PCBM thin films, P3HT thin films, and pre-annealed, post-annealed P3HT:PCBM solar cell devices. According to the transient transmissivity changes, the photoexcited carrier relaxation model can be further established to figure out the annealing process dependence of photoelectric conversion efficiency. These results provide some key information for enhancing the photoelectric conversion efficiency of the P3HT:PCBM solar cell devices.