無機螢光粉在提升矽基太陽能電池轉換效率之應用

Abstract

如何提升太陽能電池的轉換效率向來為極具挑戰的課題，矽基材太陽電池的轉換效率與矽半導體對太陽光譜中不同波長的響應呈現密切相關，如何改善矽基材對不同波長的吸收，以提高太陽能電池的轉換效率一向為熱門研究趨勢。本論文的研究之主旨為以太陽光譜轉換技術，利用網印塗佈技術結合上/下轉換螢光粉與各型元件結構之太陽電池，期望有效改善矽太陽能電池之轉換效率。 本研究利用X-光繞射進行螢光粉晶相鑑定、激發、發射與反射光譜探討螢光粉發光特性、掃描式電子顯微鏡術分析螢光粉微結構與太陽光譜模擬機進行光電轉換參數與電流-電壓曲線之量測。 此外，成本低廉、簡易可行的網印技術則被使用於將下轉換螢光粉Na2CaPO4F:Eu2+與KMGd(PO4)2:Eu3+ (M =Ca, Sr)塗佈於太陽能電池正面，利用螢光粉將太陽光譜紫外波段轉換成可見光，藉以增加矽基板轉換效率。實驗證實：經Na2CaPO4F:Eu2+塗佈後，太陽電池之效率由15.93%增至16.59%；而經三種KCaGd(PO4)2:x%Eu3+螢光粉分別塗佈後，太陽電池之轉換效率增加值分別為0.66+0.01% (x = 10)、0.71+0.01% (x = 50)與0.52+0.01%( x = 100)。 此外，本研究亦將上轉換螢光粉La2Mo2O9:Yb, R 與KCaGd(PO4)2:Yb,R (R = Er, Ho)分別網印塗佈於太陽能電池之背層，實驗證實，不同化學組成的螢光粉可以提高太陽能電池轉換效率不等，結果顯示：上轉換螢光粉塗佈太陽能電池中，以La2Mo2O9:Yb,R塗佈者，其效率分別增加0.25-0.29+ 0.01% (R = Er)與0.44+ 0.01% (R = Ho)。另一方面，以KCaGd(PO4)2:Yb,R塗佈者，其轉換效率分別增加0.44+ 0.01% (R = Er)與0.59+ 0.01% (R = Ho)。 本研究已掌握具有高效率頻譜轉換螢光材料、穩定且可靠的漿料與不同元件結構太陽電池之供應，經初步試驗證實太陽電池轉換效率之增幅最高可達5%，預期可望縮減矽太陽電池轉換效率提升所需之成本。

Given the challenges associated with global warming, the development of green energy materials has been recognized as an important issue in materials research. The solar cell is one of the devices that can be used to generate sustainable energy. The power conversion efficiency (η) from light to electricity in the silicon-based photovoltaic (PV) cells is highly dependent on the wavelength of the incident sunlight, and the η–λ relationship is characterized by the spectral responsively. In this research, we have utilized the solar spectral conversion principle and predesigned device structures to investigate the enhancement of efficiency by coating PV cells with down-conversion or up-conversion phosphors using low-cost screen-printing technique. In addition, X-ray diffraction, fluorescence and reflection spectra, and SEM imaging as well as solar simulator were used for characterizations and measurements of phosphor-coated PV cells. Composition-optimized down-conversion phosphors (i.e., Na2CaPO4F:Eu2+ and KMGd(PO4)2:Eu3+ (M =Ca, Sr)) and upconversion phosphors (i.e., La2Mo2O9:Yb,R and KCaGd(PO4)2:Yb,R (R = Er, Ho)) were selected to investigate their potential in efficiency enhancement. With coating of Na2CaPO4F:Eu2+ on the front side of PV cells, the □ value was found to increase from 15.93% to 16.59%; whereas the experimental ∆□ values were found to be 0.66+0.01% (x = 10), 0.71+0.01% (x = 50), and 0.52+0.01% (x=100), respectively, when KCaGd(PO4)2:xEu3+ was screen-printed on the surface of PV cells. Furthermore, with the coating of La2Mo2O9:Yb,R (R = Er, Ho) on the back side of PV cells, the experimental ∆□ values were found to be 0.25-0.29+ 0.01% (R = Er) and 0.44+ 0.01% (R = Ho), respectively; whereas those were found to be 0.44+ 0.01% (R = Er) and 0.59+ 0.01% (R = Ho), respectively, when KCaGd(PO4)2:Yb,R was screen-printed on the back side of PV cells. In this work, by using spectral conversion principle we have demonstrated the feasibility of efficiency enhancement in Si-based PV cells through screen-printing various phosphors onto the front/rear sides of the commodity PV cells. We have prepared phosphors with different functionalities and secured quality-reliable binders and PV cells with predesigned structures and achieved an optimal enhancement rate of 5% in experimental ∆□ value. Our pioneering research may serve as a guide and a promising alternative in reducing the cost of enhancing conversion efficiency of PV cells for the PV industries.