交流阻抗圖譜應用於染料敏化及鈣鈦礦太陽能電池之研究

Abstract

本論文利用交流阻抗圖譜研究染料敏化太陽能電池 (dye-sensitized solar cells, DSSCs) 及鈣鈦礦太陽能電池 (perovskite solar cells, PSCs)的動力學原理．於染料敏化太陽能電池領域，我們設計π-共振連接紫質中心以延伸吸光範圍，以電化學交流阻抗圖譜探討三紫質染料的烷氧推-拉基團以提升元件效能。此外，我們設計了π-共振更強的雙紫質染料(YDD6)，使吸光範圍延伸至近紅外光區，但YDD6有染料堆疊問題使電荷收集效率降低。因此，我們利用光電流與光調壓調製圖譜做進一步的分析，並加入YD2-oC8 及CD4與YDD6做共吸附以抑制染料堆疊，使元件IPCE上升。然而，為了提升元件光獲補與電荷收集能力，我們發展不同長度的一維結構二氧化鈦奈米棒¬¬－短奈米棒 (SR), 標準奈米棒(NR) 及長奈米棒 (LR)－以做為DSSC中染料吸附及電子傳輸的介質。以光電流與光調壓調製圖譜與電荷萃取技術分析奈米棒的光電特性，並依其特性建構複合層結構，設計奈米材料以導帶位能高低依序排列，因此複合層中的能階梯度能使電子傳輸更順暢的由散射層、LR、NR傳至NP，並因其形貌有利於電解液的擴散。二氧化鈦複合層結構搭配Z907染料可使效率最佳化至10 %，為未來商業化的一大進步。至於鈣鈦礦太陽能電池方面，我們利用電化學交流阻抗圖譜分析其元件光浸置於短路狀態下之動力學變化，量測取得其照光過程中的奈奎斯特圖後，以等校電路去擬合分析。我們發現於短路狀況下照光可使電洞傳輸材料Spiro-OMeTAD迅速地被氧化，因此使光電流快速地被提升。最後我們選擇於DSSC中表現相當好的二氧化鈦奈米晶粒(HD)應用於PSC元件，經鈣鈦礦CH_3 NH_3 PbCl_x I_(3-x)與HD1搭配可達12.1 %光電流轉換效率。

We applied the techniques of impedance spectroscopy to study the device kinetics of dye-sensitized solar cells (DSSCs) and perovskite solar cells (PSCs). For the DSSC part, we studied three alkoxy-wrapped push-pull porphyrins which were designed with the porphyrin core connected with π-conjugated linker to extend light harvesting ability to boot up the device performance. Furthermore, a porphyrin dimer (YDD6) was designed with strong π-conjugation to extend the light-harvesting range toward the near-IR region, but YDD6 had an aggregation problem that caused low yield of charge collection. Therefore, we introduced YD2-oC8 and CD4 together with YDD6 in a co-sensitization manner to suppress dye aggregation for improved of the device IPCE. To improve light harvesting and charge collection ability of the device, we developed one-dimensional titania nanorods of varied lengths – short rods (SR), normal rods (NR) and long rods (LR) – to serve as dye-uptake and electron-transport media for DSSC. The constructed a multi-layer configuration can profit electrolyte diffusion and correct the order of potential positions of these nanostructures, so that an appropriate sequence of energy cascade becomes established for feasible electron transport from scattering layer, LR, NR to NP. Based on a multi-layer configuration, the device efficiency with Z907 dye has been optimized to 10 %, which is a promising advancement for its future commercialization. For the PSC part, we carried out EIS measurements for devices under varied light-soaking conditions; the corresponding Nyquist plots were analyzed according to an appropriate equivalent circuit model. We found that Spiro-OMeTAD can be rapidly oxidized under light-soaking conditions to promote higher photocurrent. Finally, we applied TiO2 nanocrystals (HD), which have outstanding performance in DSSC, as a scaffold material for PSC. The best device was constructed by CH_3 NH_3 PbCl_x I_(3-x) and HD1 with power conversion efficiency 12.1 %.