光學干涉效應於有機太陽能電池之研究

Abstract

本論文利用矩陣傳輸法(Transfer matrix formalism)探討光學間隙層(Optical spacer)於高分子太陽能電池內所產生的光學干涉效應。此光學模型可用於模擬光電場於元件內的分布、被主動層吸收的總光子數，以及主動層內的激子產生率。 我們發現光學間隙層放置於主動層後方會使元件內的光電場重新分佈，進而影響元件的性能。因此，我們選擇具有高透明度及良好導電率的銦錫氧化物(Indium tin oxide)作為光學間隙層以檢驗光學干涉效應所造成的現象。從數值模擬結果發現，於主動層後方置入適當厚度的銦錫氧化物可產生更有利於載子傳輸的光電場分佈情形，能夠減少激子在金屬和有機物接觸面的消散(quenching)效應，增加有效激子數目，讓光電轉換效率有所改善。且經實驗證實，於標準元件內再將銦錫氧化物置入在主動層後方，最佳的條件下可將光電轉換效率從 3.76% 提升至 4.20% 。總而言之，我們選擇銦錫氧化物作為光學間隙層，並運用光學干涉效應使元件內的光電場重新分佈成有利於增加有效激子數目的狀態，進一步提升高分子太陽能電池的轉換效率。

In this work, we utilized the transfer matrix formalism to study the optical interference effects inside organic photovoltaic devices (OPVs). This optical simulation method is suitable for calculation of the distribution of optical field intensity, the photons absorbed inside the active layer, and thus the distribution of photo-generated excitons in the devices. We have found that the optical field intensity inside the active layer redistributes after placing an optical spacer behind the active layer. Therefore, we used indium tin oxide (ITO), exhibiting high transparency and conductivity, as an optical spacer in the OPV devices to examine the resulting optical interference effects. According to our simulation results, the spatial redistribution of optical field intensity due to the incorporation of the ITO optical spacer dramatically shifts the distribution of photo-generated excitons and the resulting beneficial distribution probably decreased the exciton quenching near the organic/electrode interface. For a 180-nm-thick active layer, which has been optimized experimentally as a standard structure, the insertion of a 120-nm-thick ITO optical spacer placed after the active layer shows an improved power conversion efficiency of 4.20% which is higher than that of the reference device (3.76%). In summary, we have demonstrated optically interference-enhanced OPVs in results of the spatial redistribution of optical field intensity by introduction of an appropriate thickness of ITO optical spacers.