對染料敏化太陽能電池之結構調整與相應電子行為分析

Abstract

為了使染料敏化太陽能電池成為更有效率的太陽能轉換元件，元件效率與穩定性的進一步提升是當前極重要的課題，於本論文中，完成三種相異結構的染料敏化太陽能電池並對各別元件的基本光電特性與電子行為進行量測觀察與分析比較。 首先，針對一般染料敏化太陽能電池元件的特性進行分析，透過改變元件製作的條件，了解相應的光電特性表徵並對目前已發展的量測方法與元件工作理論進行回顧。 接著根據過往文獻記載的實驗結果，在元件製作中使用四氯化鈦溶液對二氧化鈦奈米結晶粒工作電極表面進行處理；相較於未處理的元件，經過四氯化鈦處理的元件於光電特性上有十分顯著的增益。透過電子行為的量測並與基本元件實驗結果相較，可了解四氯化鈦所造成的增益主要是彰顯在電子電洞復合速率的抑制上，而在電子傳輸的速率上並無造成顯著地影響；再進一步從表面能態密度的量測結果可得知復合速率的抑制應與表面能態密度的減低有關。 由於電子有效擴散長度的有限性，期望能透過再進一步改善染料敏化太陽能電池的吸收特性以減少有效吸收層的厚度並同時降低元件的材料消耗，因此在基本元件中引入了具不同粒徑的二氧化鈦結晶粒作為光散射層，於本論文中對散射層製作條件進行討論；而在引入所製成均勻分佈的散射層後，於較薄吸收層的元件中確實觀測到所造成的增益，同時以進一步的光電特性結果佐證此一增益確實與期望相符，即散射層所造成。 為使電子傳輸速率能有進一步提升，本論文之第三部分透過引入陽極氧化製成之二氧化鈦奈米管狀結構完成染料敏化太陽能電池，首先針對陽極氧化條件對奈米管之影響進行探討，而完成的元件與傳統奈米晶粒之元件相較，於元件的特性上觀測到許多不同的結果，是接下來值得進一步研究的方向，最後對於不同條件所完成的元件所表現的特性於本論文中進行了一點初步的討論，亦提供奈米管元件接下來發展方向的一些參考。 於本論文中，完成了三種不同結構的染料敏化太陽能電池，並透過進階的光電特性量測方法對於結構變化所造成在電子行為上的影響進行解釋與推測，在染料敏化電池元件的發展過程中能夠提供良好的參考方向，相信一個更加理想的太陽能元件是能夠被完成與使用的。

To improve the energy transfer efficiency of dye sensitized solar cell furthermore and thus lead to more convenient usage of solar energy, complete knowledge of DSSC at present stage is necessary. In this dissertation, DSSC with three different structures were fabricated and the behaviors of electrons for each were analyzed through developed photo-electrical methods. In the start, basic properties of normal DSSC were examined and characterized. Developed theories about the working principle of DSSC, light absorption, electron injection and transportation, and the basics of measurement methods for analyzing electrons behavior were reviewed separately. With a preliminary understanding of conventional DSSC, the well known efficiency enhancement method, the passivation of TiO2 by titanium tetrachloride, was applied; the photo-electrical improvements were obviously observed from experimental results. To discover the cause of the enhancements, the electrons behaviors were measured. The recombination of electrons was inhibited when compared with non-passivated devices (near one ordered difference in the time constants) while the diffusion remains almost the same. It was thought that the inhibition of recombination be mainly due to the variation of surface states according to DOS measurement results. Because of the limitation on the diffusion length, it is preferred to achieve better absorption in thinner layer; then, a light scattering structure was applied to conventional DSSC by different sized nano-crystal. The conditions of the fabrication of scattering layer were tested and an optimized process was achieved to derive a uniform morphology of the scattering layer. With the application of the scattering layer, the enhancement of absorption was observed and the photo-voltage is enhanced in thinner layered devices. Based on observed experimental results, it was thought that the preliminary limiting factor for DSSCs at present stage be the low electron collection efficiency due to the low diffusivity in nano-crystallite film. To accelerate electron transportation, ordered nano-tube structure was fabricated and applied to DSSC successfully. Basic characterizations were done and some improvements were obtained while some disadvantages were expected to be overcome with advanced modifications in research afterward. In this dissertation, DSSCs with three different structures (conventional, scattering layer applied, and nano-tube applied) were fabricated and characterized. Different photo-electrical behaviors were observed in these devices due to the different nature of structural issues. Based on this research, it is believed that a much more efficient solar cell could be implicated.