非晶/結晶矽量子點埋入式氧化鋅薄膜之開發與於光伏元件應用

Abstract

近年來，由於矽量子點薄膜具有可大範圍調控能隙與獨特的光學特性，故已被廣泛研究並應用於多種熱門光電元件，其中於光伏元件之應用亦被視為相當具有潛力的研究之一，因其將可解決目前全矽基組成太陽能電池於短波長波段具有較大能量損耗的問題。目前矽量子點薄膜主要以矽相關介電材料為矩陣材料，雖已驗證其具有明顯光伏特性，但其特性仍受限於矩陣材料的高阻值特性，導致整體光電效益尚無法達到預期。有鑒於目前矽量子點薄膜應用太陽能電池所遭遇的瓶頸，我們提出以氧化鋅為矽量子點矩陣材料，因其不但具有矩陣材料所需必備的寬能隙特性，同時更具有高光穿透度與高度可調的電性特性，故若能成功整合矽量子點與氧化鋅薄膜，必可大幅提升矽量子點薄膜整合於太陽能電池的光電效益。此篇論文中，我們利用射頻濺鍍薄膜沉積方式，成長二十週期的[氧化鋅/矽]多層膜結構，藉由一高矽濺鍍功率與矽薄層厚度調控，於室溫下沉積出自組織矽量子點埋入式氧化鋅薄膜，並分析該薄膜於不同退火溫度下，其結晶特性、光學特性與電性特性。此外，我們亦利用調控適當的退火時間與氫退火製程，分別針對非晶與結晶矽量子點薄膜做更進一步的光電特性優化，未來若能有效整合矽量子點薄膜與非晶/微晶矽薄膜，將可邁向全矽基組成之高效率與低成本的第三代薄膜太陽能電池。

Recently, the silicon quantum dot (Si QD) thin films have been extensively studied and applied to the popular optoelectronics due to the widely tunable bandgap and unique optical properties. For example, the Si QD thin films have the great potential for photovoltaic (PV) applications because it can solve the optical loss problem in the short-wavelength range for the Si-based solar cells (SCs). So far, the Si-based dielectric materials are used as the matrix material of Si QD, and the PV properties has been demonstrated. However, the overall PV properties are still limited by the naturally high resistance of the Si-based dielectric matrix materials. In order to solve the bottleneck of the Si QD thin films applying to SC application, we propose to use ZnO as the matrix material of Si QDs since the ZnO thin film is a semiconductor material with wide bandgap, high transparency, and tunably electrical properties. These advantages are potential in improving the electro-optical properties of the Si QD thin films for SC application. In this study, the Si QD embedded ZnO thin films are fabricated by sputtering method and deposited by a [ZnO/Si] multilayer structure with 20 pairs. The self-assembled Si nano-clusters are formed in ZnO matrix by high Si sputtering power and thin Si layer thickness during deposition. The crystalline, optical, and electrical properties of the samples annealed at different temperatures are investigated and discussed. Besides, the electro-optical properties of the amorphous- and crystalline-Si QD thin films are also further improved by tuning the annealing time and using the H2 annealing process. The all Si-based third generation solar cells with high efficiency and low cost can be highly expected by integrating the Si QD embedded ZnO thin films and the a- or μc-Si thin films in the future.