奈米柱結構光電極染料敏化太陽能電池

Abstract

本論文中利用銀縮合法成為遮罩及乾蝕刻的方式在多孔隙二氧化鈦製作出表面奈米柱結構，經由不同時間下的蝕刻探討奈米柱結構對太陽能電池光電轉換效率的影響；在染料敏化太陽能電池的光電極多孔隙二氧化鈦上共嘗試了三個實驗項目 (1) 在蝕刻後保留縮合過的銀粒子遮罩，此組實驗中效率由標準試片的4.67%在經過一分鐘蝕刻後提升至最高的5.25%，而在蝕刻時間超過五分鐘後，光電轉換效率開始低於標準試片並隨著蝕刻時間增長而下降。 (2) 在蝕刻後以硝酸:水=1:10的溶液移除縮合過的銀粒子遮罩，此組實驗中效率由標準試片的4.67%在經過30秒蝕刻後提升至最高的5.14%，而在蝕刻時間5分鐘的情形下情形類似於第一組實驗下降至約與標準片同樣。 (3) 直接對多孔隙二氧化鈦作電漿乾蝕刻，效率由標準試片的4.67%經過直接蝕刻後效率隨著蝕刻時間的上升而下降至最低3.62%，由此組實驗中我們可以確定光電轉換效率提升的原因是因為表面結構的影響而非電漿的表面處理。 我們從以上三組實驗中發現藉由表面奈米柱結構增加光散射的機會，可提升光電流並增進效率，但乾蝕刻的時間需控制在約一分鐘下，才能避免因蝕刻過多的多孔隙二氧化鈦導致染料吸附量過低而降低光電流。

Nanopillar structures are fabricated on nanoporous TiO2 by inductively coupled plasma (ICP) etching using silver-shrunk nanodot shadow masks. The dye-sensitized solar cell (DSSC) conversion efficiency is highly related to the etching time. Dye-sensitized solar cells are made with nanopillar nanoporous TiO2 photoanodes. Experiments are conducted in following conditions. (1) The shrunk silver nanodot shadow masks are retained on the surface of nanoporous TiO2 photoanodes after ICP etching. The reference sample conversion efficiency is 4.67% (without silver nanodot and ICP etching), and the cell efficiency rises to the highest efficiency of 5.25% after 1 minute dry etching with silver nanodot shadow masks. Then the efficiency reduces again when etching time exceeds 1 minute. (2) The silver nanodot shadow masks are removed by the HNO3:H2O=1:10 solution after the ICP etching process. The cell efficiency rises to 5.14% after 30 second ICP etching. Then the efficiency drops to 4.72% after 5 minutes of ICP etching. (3) The nanoporous TiO2 are directly treated using ICP plasma without silver sphere mask. The conversion efficiency is reduced monotonically from 4.67% (reference sample) to 3.62%(after etching 1 minute). From the experiments, the enhanced cell efficiency is due to the nanopillar structure instead of the plasma treatment. The nanopillar structure would increase the light scattering, thereby improving the photocurrent and the conversion efficiency. When the etching time is too long, the thickness of nanoporous TiO2 is reduced, leading to the decrease of total amount of absorbed dyes and the light being absorbed by the dyes, thereby reducing the cell photocurrent and efficiency.