玻璃衬底上p型自掺杂硅纳米线阵列的制备及在径向异质结光伏器件中的应用

Due to the unique optical and electrical characteristics, radial pn junction-based photovoltaic devices constructed on nanowires exhibit the incomparable ratio of potential performance to cost over traditional planar pn junction devices. Accordingly, how to cost-effectively grow large-scale, high quality silicon nanowire arrays with controlled structural parameters on low-cost substrates instead of silicon wafers normally used, and then to fabricate optically and electrically optimized radial pn junction is much more meaningful for the healthy development of the photovoltaic industry. In this project, we are going to prepare high quality p-type self-doped silicon nanowire arrays with controllable structural parameters on glass substrates via a home-built inductively coupled plasma (ICP) system and employing aluminum as the catalyst. Here the plasma is ignited by a single inductance coil placed in the chamber and the aluminum catalyst is patterned using the self-assembled single-layered SiO2 nanospheres. Relative to the commonlly used approach of growing silicon nanowire arrays, i.e., the thermal chemical vapor process catalyzed by photolithographically patterned Au, the proposed method in this project facilitates the preparation of the wire arrays with high electrical quality and low cost. After achieving the high quality silicon nanowire arrays, the radial heterojunction configuration will be introduced through conformally covering an intrinsic crystalline silicon (c-Si) light absorption and carrier generation layer, a hydrogenated amorphous silicon (a-Si:H) transition and passivation layer, and an n-type hydrogenated amorphous silicon carbide (a-SiC:H) window and emitter layer in sequence. Here it is worth noting that all layers will be subsequently deposited using ICP through varying the precursor gases and adjusting the position of the substrate away from the inductance coil to choose appropriate radicals. Compared to homojunctions, the heterojunctions proposed utilize a-SiC:H, a wide bandgap material, to alleviate the light absorption in the emitter, which would be met in the homojunction configuration of the silicon nanowire array solar cells (Here one must note that a large part of light is absorbed on the silicon nanowire surface if homojunction is adopted due to the absorption enhancement mechanism in silicon nanowire arrays). Furthermore, its wide bandgap can significantly boost the open circuit voltage. The a-Si:H layer can passivate the interface defects between a-SiC:H and the c-Si absorption layer. Accordingly, the proposed radial heterojunction configuration based on a-SiC:H and a-Si:H is expected to significantly improve the cell performance over the homojunction devices.

由于其独特的光、电学性质，基于纳米线结构的径向pn结光伏器件具有传统平面结器件所无法比拟的潜在性价比。如何结合理论优化设计的结果，利用低成本的工艺过程，在廉价衬底上制备大面积、高质量、结构参数可控的硅纳米线阵列，并通过引入光、电学参数优化的径向pn结从而获得高的光电转换性能，对光伏产业的持续健康发展具有重要意义。本项目拟利用自主设计、组装的内置单圈电感耦合等离子体化学气相沉积装置，以自组装单层SiO2纳米球为掩膜版图案化的铝作催化剂，在玻璃衬底上制备高质量、结构参数可控的p型自掺杂硅纳米线阵列。从而克服利用传统热化学气相过程，以光刻技术图案化的Au催化生长硅纳米线高的成本和低劣的电学质量。在高质量硅纳米线阵列获得的基础上，通过依次在纳米线表面包覆本征晶硅光吸收\载流子产生层、氢化非晶硅钝化\过渡层及n型氢化非晶硅碳窗口\发射层，制备具有高效光管理和载流子收集的径向异质pn结光伏器件。

由于其独特的光、电学性质，基于纳米线结构的径向pn结光伏器件具有潜在的,传统平面结器件所无法比拟的高性价比。本项目以用简单的方法、廉价的催化剂，在较低的生长温度下制备高质量硅纳米线阵列为研究切入点，系统地开展了一系列探索性工作，取得了以下重要的研究成果：（1）在管式炉中，以铝做催化剂，实现了p型自掺杂硅纳米线阵列的生长；（ii）在结构和性能优化的p硅纳米线表面，利用电感耦合等离子体增强化学气相沉积技术依次包覆晶化硅和n型a-SiC:H层，从而实现了径向异质pn结的制备。所制备的原型器件的光电转换效率约3.6%；（iii）系统地开展了光与半导体纳米/亚微米结构相互作用的研究工作，建立了完整的物理图像，为相关高性能半导体纳米/亚微米光吸收体的设计和制备提供了一般性的指导。