用奈米結構擷取太陽能

Abstract

第一個工作我們利用水熱法成長氧化鋅奈米線在市售五吋單晶矽太陽能電池上。其附合結構，包含氧化鋅奈米線/氮化矽抗反射層/微米坑洞，使電池的短路電流提升到38.45毫安培/每平方公分，開路電壓609毫伏特，及光電轉換效率14.04%，在高角度60度光入射測試只有損失5.3%的短路電流。在第二個工作，我們使用奈米球製作奈米柱與奈米牆複合結構作為抗污封裝玻璃，經過六星期的戶外測試，電池仍能可以維持98.8%原本的效率。第三個工作我們利用硒化銅銦鎵量子點設計梯流效應降低染料敏化太陽能電池的暗電流，使電池的短路電流提升到15.27毫安培/每平方公分，開路電壓762毫伏特，及光電轉換效率8.02%，最後一個工作我們利用氮參雜的石墨烯搭配白金作為背電極，其梯流效應，高催化特性及高反射率使得染料敏化太陽能電池的光電轉換效率得到大幅的提升。

In first work, we employ a ZnO nanorod/Si3N4-coated Si microgroove-based hierarchical structure (HS) for a light-harvesting scheme in 5 inch single crystalline Si solar cells. ZnO nanorods and Si microgrooves were fabricated by a simple and scalable aqueous process. The excellent light-harvesting characteristics of the HS, such as broadband working ranges and omnidirectionality have been demonstrated using external quantum efficiencies and reflectance measurements. The solar cells with the hierarchical surface exhibit excellent photovoltaic characteristics, i.e., a short-circuit current (JSC) of 38.45 mA/cm2, open-circuit voltage of 609 mV and conversion efficiency of 14.04%. As incident angles increase from 0o to 60o, only 5.3% JSC loss is achieved by employing the hierarchical surface, demonstrating the enhanced omnidirectional photovoltaic performances, also confirmed by the theoretical analysis. A viable scheme for broadband and omnidirectional light harvesting using the HS employing microscale/nanoscale surface textures on single crystalline Si solar cells has been demonstrated. In second work, fused-silica packaging glass fabricated with a hierarchical nanostructure was found to exhibit superior antireflective and self-cleaning properties. The nanostructure was achieved by colloidal lithography and reactive ion etching techniques, displaying the stacking of ultra-thin nanorods on top of nanowalls. Commercial Si solar cells covered with the hierarchically structured packaging glass exhibit enhanced photovoltaic performances, and the enhancement becomes increasingly prominent after 6 weeks of outdoor exposure. Similar improved performances were attained by GaAs-based solar cells with the same hierarchical glass. The enhanced device performances indicate that the nanostructured surface can effectively repel polluting dust/particles and facilitating optical waves propagating through the fused-silica, which was confirmed by numerical analyses. In third work, Ga-rich CuIn(1-x)GaxSe2(CIGS) quantum dots (QDs) with a wide bandgap of 1.58eV were utilized in dye-sensitized solar cells for energy harvesting. Ga-rich CIGS QDs at TiO2 photoanodes afford the recombination reduction and thus suppress the dark current, leading to the increase of short-circuit current from 14.47 to 15.27 mA/cm2 and open-circuit voltage from 751 to 762mV. This is due to well-adjusted conduction band minimum of Ga-rich CIGS QDs between that of TiO2 and excited state oxidation potential of N719, enhancing the photoelectron collection and suppressing electron back-transfer from TiO2 to oxidized redox species in the electrolyte. In final work, nitrogen-doped graphene (NGR) was utilized in dye-sensitized solar cells for energy harvesting. NGR on Pt-sputtered fluorine-doped tin oxide substrate (NGR/Pt/FTO) as counter electrode (CE) achieves the high efficiency of 9.38% via the nitrogen doping into graphene. This is due to (i) the hole-cascading transport at the interface of electrolyte/CEs via controlling valence band maximum of NGR located between the redox potential of I-/ I- redox couple and the Fermi level of Pt by nitrogen doping, (ii) the extended electron transfer surface effect provided by large-surface-area NGR, (iii) the high charge transfer efficiency due to superior catalytic characteristics of NGR via nitrogen doping, and (iv) the superior light-reflection effect of NGR/Pt/FTO CEs, facilitating the electron transfer from CE to I3- ions of the electrolyte and light absorption of dye. The result demonstrated that the NGR/Pt hybrid structure is promising in the catalysis field. Keywords: antireflective coating, ZnO nanorods, dye-sensitized solar cell, nitrogen-doped graphene, CIGS, quantum dot.