採用散射紅光色彩轉換層之固態白光有機電化學元件

Abstract

以離子性過渡金屬錯合物為材料之固態有機白光電化學元件能產生高效率的白光電激發光。近年來，有機藍光電化學元件結合了在氧化銦錫(ITO)和玻璃基板之間插入嵌入式紅光色彩轉換層，已從實驗中得到大於12％的外部量子效率。然而，由於複合區移動所造成的微共振腔效應，影響了有機發光電化學元件隨時間變化的電激發光頻譜。此外元件的效率，應進一步改進，以符合實際用。 在此實驗中，兩種不同尺寸的TiO2奈米粒子被加入至紅光色彩轉換層中，以提高元件性能。大尺寸的TiO2奈米粒子(250奈米)，具有散射效果並且能將光重新導向通過紅光色彩轉換層，而進一步增加了可提取的光。小尺寸的奈米粒子(25奈米)，則是增加紅光色彩轉換層的折射率和提高靠近ITO層波導模態中依指數遞減的場分量之光強度。因此，更多被侷限在波導模態中依指數遞減的場之光可以利用散射的方式再輸出至外部模態。而白光有機電化學元件採用散射奈米粒子的紅光色彩轉換層所達到的外部量子效率峰值和功率效率，分別為20.0％和39.5流明/瓦。此外隨著具散射功能的大尺寸奈米粒子，平均分散不同方向上的光，所產生的白光是幾乎不隨時間而改變的。這些結論證明，有機藍光電化學元件結合散射的紅光色彩轉換層在提供高效率和穩定白光是有效果的。

Solid-state white light-emitting electrochemical cells (LECs) based on ionic transition metal complexes are capable of generating efficient white electroluminescence (EL). Recently, blue-emitting LECs combined with embedded red color conversion layers (CCLs), which were inserted between indium tin oxide (ITO) and glass substrate, have been reported to offer external quantum efficiency (EQE) >12%. However, the output spectrum of EL from such white LECs changed with time due to altered microcavity effect when recombination zone was moving. Furthermore, device efficiency should be further improved to realize practical applications. In this work, TiO2 nanoparticles (NPs) of two sizes are incorporated in red CCLs to improve device performance. Large NPs (250 nm) can scatter and redirect the light passing through red CCL and further enhance the extracted light. Small NPs (25 nm) increase the refractive index of red CCL and raise the amount of light intensity in the evanescent tail of waveguide mode near ITO layer. Therefore, more trapped light in the evanescent tail of waveguide mode can be recycled to external mode by scattering. Peak EQE and power efficiency of white LECs employing scattering red CCLs reach 20.0% and 39.5 lm W-1, respectively. Furthermore, with scattering NPs to average EL in different directions, white EL is almost invariant with time. These results show that blue-emitting LECs combined with scattering red CCLs would be effective to provide efficient and stable white EL.