利用干涉效應修改頻譜之純主體近紅外固態有機發光電化學元件

Abstract

固態近紅外有機發光電化學元件(Solid-State NIR LECs)在近紅外光源應用上擁有很大的發展潛力，因具備以下幾項優點，例如：元件結構簡單、低操作電壓及可適用在大尺寸可撓性基板等。但對於一般主客體摻雜的近紅外有機發光電化學元件來說，以操作電壓增加來達到更高的近紅外光輸出功率時，明顯會受到主體殘留光增強之問題。因此，在主客體摻雜的近紅外有機發光電化學元件只能靠犧牲光色純度來提高近紅外光輸出功率。為了在不犧牲輸出的光色純度之條件下，來提升元件近紅外光輸出功率，本研究提出了一種光學方法，是藉由調整元件發光層厚度來改變微共振腔效應，並從純主體紅光元件得到穩定的近紅外電激發光頻譜，是藉由調整元件發光層厚度來使發光波峰移動而改變光色，最後能在近紅外光波段產生建設性干涉來得到穩定的近紅外電激發光頻譜，而此近紅外電激發光頻譜是經由微共振腔效應所產生，也就是元件內部光學干涉效應造成，並與操作電壓較無關。因此，在減少犧牲掉光色純度之條件下，比起先前提出的主客體摻雜的近紅外有機發光電化學元件能達到二十餘倍的近紅外光輸出功率提升，實驗結果表示純主體紅光元件可經由改變微共振腔效應來達到修改頻譜之效果，所以此方法將能得到更高的近紅外光輸出功率而且不受主客體摻雜的近紅外光元件之主體殘留光影響。

Solid-state near-infrared (NIR) light-emitting electrochemical cells (LECs) possess great potential in applications of NIR light sources due to their simple device structure, low operating voltage and compatibility with large area and flexible substrates. However, common host-guest NIR LECs suffer from the problem of significantly enhanced residual host emission when increasing bias voltage to achieve higher NIR light output. Higher NIR light output can only be obtained at the expense of spectral purity in host-guest NIR LECs. To enhancing NIR light output of LECs without sacrificing spectral purity significantly, a novel approach to generate NIR EL from host-only red-emitting LECs by adjusting device thickness to modify microcavity effect is proposed. NIR EL from host-only red-emitting LECs can be realized by adjusting device thickness to shift peak wavelength for constructive interference at NIR spectral region. NIR EL resulted from microcavity effect is relatively insensitive to bias voltage. Therefore, without losing spectral purity significantly, 20X enhancement in NIR output has been obtained in comparison to previously reported value from host-guest NIR LECs. These results reveal that tailoring EL spectra of host-only red-emitting LECs via modifying microcavity effect would be a promising way to generate higher NIR light output without suffering from residual host emission problem of host-guest NIR LECs.