Excimer laser surface treatment on TiO2 nanoporous layers for dye-sensitized solar cell application

本論文討論經KrF準分子雷射表面處理的二氧化鈦光電極製作之染料敏化太陽能電池的特性參數及效率。本研究所研究的雷射表面處理參數群組有三種: 1.第一組為定雷射能量80mJ/cm2，改變處理發數0、2800、5600、11200、16800、22400發，最佳條件為表面處理11200發的元件，光電流提升約13%、光電轉換效率則提升了24%。 2.第二組為變雷射能量0、40、80、120、160、200mJ/cm2，表面處理發數均為1000發，最佳條件為雷射能量120 mJ/cm2的元件，光電流提升約11 %、光電轉換效率則提升了20 %。 3.第三組為變雷射能量0、40、80、120、160、200mJ/cm2，表面處理發數均為1發，光電流與光電轉換效率與標準片相比無顯著提升。 經較高發數的雷射表面處理二氧化鈦光電極的染料敏化太陽能電池在短路電流 (Short circuit current)、開路電壓(Open circuit voltage)、理想因子(Fill factor)、效率均有提升，原因在於雷射處理二氧化鈦薄膜粗糙化的表面使得長波長區段的光利用率提升、二氧化鈦/染料/電解液的接面電阻下降、二氧化鈦表面缺陷的減少。但是在一發的雷射表面處理下，僅僅只觀察到開路電壓的提升，短路電流、理想因子和效率則均無明顯差異。從電池的特性參數結果來看，雷射應用於二氧化鈦光電極的表面處理，發數與能量間須選擇一個最佳搭配，才能有助於提升電池的整體效能。This thesis discusses the characteristic parameters of dye-sensitized solar cells (DSSCs) made with KrF exicmer laser treated TiO2 photoanodes. Three different sets of experiments are conducted to identify the influences of laser treatment parameters. 1.The laser power density is fixed at 80mJ/cm2, and the number of laser irradiation pulses is varied as 0、2800、5600、11200、16800、22400 shots. The best cell efficiency is achieved with 11200 pulses of laser irradiation. The short-current density increased by ~13% and the conversion efficiency increased by ~24%. 2.The irradiation laser pulse number is fixed at 1000, and the power density is varied as 0、40、80、120、160、200 mJ/cm2. The best cell efficiency is obtained when the TiO2 photoanode is treated with a laser power density of 120 mJ/cm2, the short-current density increases by ~11% and conversion efficiency increases by ~20%. 3.The irradiation laser pulse number is fixed at 1, and the laser power density is varied as 0、40、80、120、160、200 mJ/cm2. No remarkable enhancement of short-current density and conversion efficiency is observed. The dye-sensitized solar cells made with TiO2 photoanodes treated by multiple laser pulses show remarkable enhancement of short-circuit current, open-circuit voltage, fill factor and conversion efficiency. The rougher TiO2 surface morphology enhances the light scattering and light trapping, thereby improving the photocurrent levels and conversion efficiencies. Surface re-melting and solidification process also changes the surface status, reducing both the resistance of TiO2/dye/electrolyte interface and the TiO2 surface defect density. This leads to better fill factor and open circuit voltage. The open circuit voltage increases for DSSCs with photoanodes irradiated by only one laser pulse. However, in this case, the overall performance of solar cells is not improved. From the experimental results we can conclude that we need both appropriate laser power density and number of laser pulses to enhance the efficiency of DSSCs