奈米環形槽陣列之表面電漿子特性研究及其於氫化非晶矽薄膜太陽能電池之應用

Abstract

本論文研究週期性奈米環形槽陣列之背反射電極的光學性質及其於氫化非晶矽薄膜太陽能電池之應用。環形槽係指一奈米孔洞內有奈米柱之結構，孔洞之直徑即為環形槽外徑，奈米柱之直徑即為環形槽內徑。首先我們固定結構深度，維持環形槽內徑及環形槽外徑之比例為0.7左右，發現在不同週期(200 nm、400 nm、500 nm、1000 nm)下，隨著週期越大，太陽能電池之光電轉換效率越高。從鍍銀環形槽陣列之積分反射及徑向反射頻譜上，我們發現在某些波長下反射率有突降(dip)的現象，突降發生的波長與週期有關。此反射率突降產生的原因是因為週期性結構產生表面電漿子共振。在霧度頻譜上，霧度會隨著週期增加而提昇。外部量子效率量測中發現，電流主要在紅光區段有所提昇，而週期越大，紅光區段的增益也越高，可歸因於基板的表面電漿子效應及霧度的提昇所致。 接著我們比較在週期固定為1000 nm，環形槽外徑為900 nm，觀察三種不同環形槽內徑之環形槽陣列鍍銀後的光學特性。我們在入射角固定為5度之變角度反射率頻譜中發現，相較於鍍銀後之奈米洞陣列，鍍銀後之奈米環形槽陣列反射角大於40度下有較大的反射率，由此可知，相較於奈米洞陣列，奈米環形槽陣列可提昇光的散射。以有限時域差分法分析鍍銀後之奈米環形槽陣列及奈米洞陣列發現，奈米環形槽陣列可以將入射光散射至較大角度，而其表面電漿子之近場強度及分佈也與奈米洞陣列有所不同。 最後我們發現三種製作於奈米環形槽陣列背反射電極的氫化非晶矽薄膜太陽能電池在光電轉換效率上皆優於製作於與環形槽外徑相同之奈米洞陣列背反射電極的電池。與製作於平面結構背反射電極的電池相比，環形槽內徑為630 nm的環形槽陣列雖使開路電壓從0.83 Ｖ微降至0.81 V，但電池效率由4.27%提昇至5.94%(提昇39%)，短路電流從9.42 mA/cm2上升至11.11mA/cm2(提昇18%)，填充因子則由54.61%昇至66.01%(提昇21%)。

Periodic anti-ring arrays were fabricated and applied as the back reflectors in hydrogenated amorphous silicon thin film solar cells. The anti-ring is composed of a nanopillar inside a nanohole. The outer diameter of the anti-ring is defined as the hole diameter, and the inner diameter of the anti-ring is defined as the diameter of the nanopillar. First, we studied the performance of the cells fabricated on anti-ring arrays with periods of 200 nm, 400 nm, 500 nm, and 1000 nm, respectively while fixing their depth at about 100 nm and ratio of the inner diameter and outer diameter at about 0.7. We found that the larger the period, the higher the cell power conversion efficiency. Several dips were observed in the reflectance spectra of Ag-coated anti-ring arrays. The dip is caused by the excitation of the surface plasmon resonance modes and its corresponding wavelength is related to the period of the anti-ring array. The haze is also enhanced when the period increased. As a result, enhancement of external quantum efficiency was observed in the red to infrared region. The larger the period, the greater the enhancement. Next, we studied the effect of the inner diameter size of the anti-ring while keeping the period at 1000 nm and the outer diameter at 900 nm. The angle-resolved reflectance spectra reveals that the reflectance at large angle(>40o) is enhanced when the center pillar presents. The cells fabricated on the anti-ring back reflector outperform that fabricated on the nanohole back reflector (i.e. without center pillar). The cell fabricated on anti-ring back reflector with anti-ring inner diameter of 630 nm exhibits a Voc of 0.81 V, a Jsc of 11.11 mA/cm2, a FF of 66.01% and a power conversion efficiency of 5.94%, which is 39% improvement compared to the cell fabricated on the flat back reflector. Simulation based on Finite-Difference Time-Domain (FDTD) shows that the anti-ring array back reflector can scatter more light into large angle compared to the nanohole back reflector. The intensity and distribution of the surface plasmon polariton are altered due to the presence of the center pillar.