上/下轉換螢光體之製備及發光特性與其在太陽能電池之應用

Abstract

本研究利用固態合成法成功地製備Yb3+/Er3+共摻或Eu3+單摻等兩系列磷酸鹽與鋅酸鹽螢光體，總計涵蓋KCaGd(PO4)2:Yb3+,Er3+、KCaGd(PO4)2:Eu3+、KSrGd(PO4)2:Yb3+,Er3+、KSrGd(PO4)2:Eu3+、Y2BaZnO5: Yb3+,Er3+、Y2BaZnO5: Eu3+、Gd2BaZnO5:Yb3+, Er3+與Gd2BaZnO5: Eu3+。我們利用X光繞射、掃描式電子顯微鏡、螢光與漫反射光譜及積分球對上述螢光體進行晶相結構與純度、表面形態與發光特性分析鑑定，並擇優篩選以應用於太陽能電池轉換效率之提升。通常以980 nm波長激發Yb3+/Er3+共摻螢光體，可獲得520~560 nm綠光放射與630~680 nm的紅光放射；而以紫外光激發Eu3+活化螢光體，可獲得紅光放射。 本研究基於螢光體為吸光層，將矽晶太陽能電池頻譜響應較差的紫外光轉換成可見光波段之原理，利用網印技術將螢光粉/漿料塗佈於多晶矽太陽能電池表面，並進行電流-電壓曲線與效率量測，以探討其提升太陽能電池光電轉換效率之可行性；另一方面，本研究亦探討奈米與微米KCaGd(PO4)2: Eu3+螢光體粒徑大小對太陽能電池的轉換效率的影響。

To investigate the potential application of up- and down-conversion phosphor coating in enhancing the performance of photovoltaic (PV) cells, we have successfully synthesized several phosphate and zincate phosphors with the composition of KCaGd(PO4)2:Yb3+,Er3+, KCaGd(PO4)2:Eu3+, KSrGd(PO4)2:Yb3+, Er3+, KSrGd(PO4)2:Eu3+, Y2BaZnO5:Yb3+,Er3+,Y2BaZnO5:Eu3+, Gd2BaZnO5:Yb3+, Er3+ and Gd2BaZnO5:Eu3+. All of the phosphors were characterized by X-ray powder diffraction (XRD), photoluminescence (PL) and diffuse reflectance spectroscopy (DR), scanning electron microscopy (SEM) as well as integrating sphere. With a screen process we have fabricated silicon-based solar cells with coating of rare-earth-doped phosphors. Under 980 nm laser excitation via an up-conversion process, the Yb3+/Er3+ co-doped phosphors were found to show two main emission bands in the green region (520~ 560 nm) and red region (630~680 nm). On the other hand, the Eu3+ doped phosphors could be excited with ultraviolet radiation and exhibit a red emission. In an attempt to improve the conversion efficiency (η) of photovoltaic (PV) devices, a mixture of phosphors and binder was prepared and screen-printed on the surface of PV silicon wafers and the I-V curves and the η value of the PV devices was measured with solar simulator. With this spectral-conversion layer formed, the short-wavelength radiation of the sun light can be converted into visible light and reused by the PV cells to reconvert into electricity by the photovoltaic devices. The research also attempts to investigate the effect of particle size of phosphors size on the enhancement of optoelectronic conversion efficiency.