1. UKM Learning and Research Repository
2. PHD Thesis / Tesis PHD
3. Faculty of Science and Technology / Fakulti Sains dan Teknologi

Title:	Vertically aligned silicon nanowires for solar cell applications
Authors:	Eman S.M. Ashour (P52759)
Supervisor:	Mohd Hafidz Ruslan, Assoc. Prof. Dr.
Keywords:	Vertically aligned silicon nanowires Silicon nanowires Solar cell applications Nanowires
Issue Date:	15-Sep-2013
Description:	Silicon nanowires (SiNWs) serve as future building blocks for cost effective third generation solar cell. Superior optical properties such as a low reflection and broadband light absorption make SiNWs to be good candidates for use as Anti Reflection Coating (ARC). Many synthetic strategies have been successfully developed to obtain vertical arrays of SiNWs, using both the bottom-up and the top down approaches. As a top-down approach, metal-assisted wet-chemical etching of silicon substrates is considered as a promising method to achieve precise positioning of aligned SiNWs as well as control of diameter, length, spacing, and density, avoiding high-cost and low-throughput conventional lithographic processes. To date, SiNWs solar cell do not reach the efficiencies of conventional cells. This low efficiency is mainly caused by the surface recombination velocity which strongly increases when using SiNWs ARC, due to the large surface area. It is necessary, therefore to develop passivation approach to the SiNWs surface, minimizing the surface states. This thesis is concerned with the process optimization of SiNWs synthesis by metal-assisted wet-chemical etching. Most of the synthesis conditions for SiNWs fabrication have been studied in details as a function of growth parameters such as temperature, etching time, etching solution concentration and starting substrate characteristics. In addition, SiNWs solar cell performance has been proposed as a function of SiNWs length. The optimized growth of SiNWs that ensures extremely low antireflective properties without degrading electrical performance is then used to demonstrate different solar cell devices. SiNWs surface passivation has been investigated using four different structures. Porous SiNWs, core /shells structure such as a_Si:H /SiNWs, SiNx/SiNWs and ZnO_Al/SiNWs have been employed to silicon solar cell, and hence, comparing their optical and electrical features. Owing to the results obtaining SiNWs with desired length can be achieved by controlling either the etching time or etching temperature, or both. The vertical aligned SiNWs structure was superior accomplished by the adjustment of etching solution concentration in specific ranges AgNO3 (0.015 - 0.03 M) and HF (4.5 - 5.25 M). The porous SiNWs arrays show excellent antireflection property and give a low reflection loss of 3.46% within the wavelength range of 250-1000 nm. The solar cell based on the porous SiNWs arrays show PCE of 9.12% with Jsc of 31.71mA/cm² and Voc of 552mV under illumination. This is first time this structure is fabricated and its performance highlights the ability of mesporous to passivate SiNWs surface. The a-Si:H/SiNWs solar cell demonstrates 12%, 15% and 37 % increment in Jsc, Voc and PCE, respectively comparing to SiNWs planar device. On the other hand SiNx/SiNWs solar cell shows improved Jsc by 15%, Voc by 7% and effeciency by 31%. An overall PCE of 6.73% is attained for ZnO-Al/SiNWs device. Reduction in the surface recombination centres by ZnO-Al shell is the main cause of such improved PCE compared to SiNWs alone. In conclusion, the data obtained from this research provides valuable information on SiNWs synthesis, porous SiNWs formation, optical and electrical characteristics and surface passivation of SiNWs via different techniques to enhance SiNWs solar cell performance.,Ph.D.
Pages:	201
Call Number:	TK7874.85.A837 2013 tesis
Publisher:	UKM, Bangi
Appears in Collections:	Faculty of Science and Technology / Fakulti Sains dan Teknologi

Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.