"Cu(In, Ga)Se2薄膜太陽能電池與TiNb2O7鋰離子電池陽極材料之製備與特性分析"

Abstract

本論文針對Cu(In, Ga)Se2薄膜太陽電池之光吸收層材料及鋰離子電池之負極材料TiNb2O7進行製備與特性分析。本論文第一部分為了提高溶液塗佈法製備之Cu(In, Ga)Se2薄膜的光電性能，將釤離子添加到Cu(In, Ga)Se2薄膜中。釤(Sm)離子的摻入促進了硒化反應過程中Cu2-xSe相的形成，從而促進了Cu(In, Ga)Se2晶粒的生長。摻雜釤離子的Cu(In, Ga)Se2薄膜具有平整之表面形貌，從而降低了Cu(In, Ga)Se2/ CdS界面中的缺陷濃度。與無摻雜的Cu(In, Ga)Se2薄膜相比，將0.5 mol%釤離子摻雜到Cu(In, Ga)Se2薄膜中後，製備的太陽能電池的光電轉換效率提高了26.6% (從8.62%提高到10.91%）。本論文的第二部分中，探討在溶液塗佈法製備之前體薄膜中摻入銅銦後端層對Cu(In, Ga)Se2薄膜的特性影響。銅銦後端層的摻入增強了硒化反應過程中鎵離子和銦離子之間的內部擴散，在製備的薄膜中建立了梯度分佈的能隙分佈。梯度能隙減少了載子的再結合並改善了太陽能電池的載流子收集。與原始的前驅體膜相比，具有銅銦後端層的前驅體膜將製得的太陽能電池的轉換效率從8.34%提高到11.13%。 本論文的第三部分中，利用了微乳膠製程來製備TiNb2O7奈米粉體。在微乳膠製程中，含有奈米級油包水液滴的熱力學穩定溶液提供了獨立的環境作為奈米反應器可有效防止顆粒生長。微乳膠製程製備的TiNb2O7奈米粉體具有大的比表面積，可提供大的活性面積與電解液接觸，從而增加了鋰離子的擴散性。微乳膠製程製備的TiNb2O7奈米粉體在0.1 C下表現出令人滿意的放電容量。本論文的第四部分中，探討經過後處理製程製備之TiNb2O7粉體的特性研究。經過後處理後，因為氧空位的形成增加了TiNb2O7能帶中的施子(donor)能階，降低了製備樣品的能隙值。透過良好的控制TiNb2O7粉體中氧空位的濃度，有效降低了製得電池的電荷轉移阻抗。與原始的TiNb2O7粉體相比，還原的TiNb2O7粉體所製備的電池在20 C下的倍率性能被改善。本論文的第五部分中，利用將塗層沉積在TiNb2O7粉體的表面上增強了製備電池的循環壽命。塗層為電化學反應提供了額外的氧化還原對，可補償由於塗層而導致的TiNb2O7放電容量下降。塗層減少了TiNb2O7與電解質直接接觸，從而抑制TiNb2O7與電解質的界面反應。當用塗層塗覆TiNb2O7時，所製備的電池在0.2 C下循環100圈的容量保持率顯著的被改善。本論文成功開發製備高效率Cu(In, Ga)Se2太陽電池之相關製程技術，並建立完整的TiNb2O7負極材料製備技術，可應用於改善Cu(In,Ga)Se2太陽電池與鋰離子電池之元件表現與發展應用。

Cu(In, Ga)Se2 thin films and TiNb2O7 powders were prepared for the application of Cu(In, Ga)Se2 solar cells and lithium-ion batteries, respectively. For improving the photovoltaic properties of the solution-based Cu(In, Ga)Se2 films, samarium ions were added into Cu(In, Ga)Se2 films in the first section of this thesis. The incorporation of samarium ions facilitated the formation of the Cu2-xSe phase during the selenization reaction to promote the growth of Cu(In, Ga)Se2 grains, thereby decreasing defect density in the Cu(In, Ga)Se2/cadmium sulfide (CdS) interface and the absorber layers. Compared with pristine Cu(In, Ga)Se2 films, the conversion efficiency of the prepared solar cells increased by 26.6% (from 8.62% to 10.91%) when 0.5 mol% samarium ions were doped into Cu(In, Ga)Se2 films. In the second section, the incorporation of copper-indium back-end layer in the precursor films for preparing Cu(In, Ga)Se2 films was investigated. The incorporation of copper-indium back-end layer enhanced the internal diffusion between gallium-ion and indium-ion during selenization reaction to build up a gradient profile of bandgap distribution in the prepared films. The gradient bandgap reduced the carrier recombination and improve the carrier collection of solar cells. In contrast to the pristine precursor films, the precursor film with a copper-indium back-end layer increased the conversion efficiency of prepared solar cells from 8.34% to 11.13%. In the third section, the modified microemulsion process was utilized to prepare TiNb2O7 nanoparticles. In the microemulsion process, the thermodynamically stable solution containing nano-sized water-in-oil droplets provided an independent environment as nanoreactors to prevent particle growth. The microemulsion-derived TiNb2O7 nanoparticles possessed a large specific surface area for providing a large contact area between the active materials and electrolyte, thereby increasing the diffusivity of lithium ions. The microemulsion-derived TiNb2O7 nanoparticles exhibited satisfactory discharge capacities at 0.1 C. In the fourth section, the preparation of TiNb2O7 powders via a post treatment process was investigated. After the post treatment process, the bandgap values of prepared samples were decreased because the formation of oxygen vacancies increased the impurity level in the forbidden gap of TiNb2O7. The well-controlled amounts of oxygen vacancies in TiNb2O7 powders were effectively reduced the charge transfer resistance of prepared batteries. In comparison to the pristine TiNb2O7 powders, the rate capability at 20 C of the prepared batteries containing the reduced TiNb2O7 powders was improved. In the fifth section, coating was deposited on the surface of TiNb2O7 powders for enhancing the cyclability of prepared batteries. A coating provided additional redox couples for electrochemical reactions to compensate the degraded discharge capacity of TiNb2O7 caused by the coating layers. A coating prohibited direct contact between TiNb2O7 and electrolyte to suppress interface reactions. When TiNb2O7 was coated with a coating, the capacity retention of prepared batteries at 0.2 C for 100 cycles was significantly improved. This thesis demonstrated that the new methods for enhancing the conversion efficiency of Cu(In, Ga)Se2 solar cells and the novel preparation processes for synthesizing TiNb2O7 powders with high electrochemical properties and a long-term cyclability were successfully developed.