Studies of various alkali metal oxides containing calcium silicate glasses as substrate for solar cell application

Abstract

Extensive research is going on in the field of thin film solar cells (TFSCs) to improve its efficiency and reduce the cost. Various groups observed that the film grown on soda lime glass (SLG) substrate had a lt112gt oriented texture with absence of aggregate structures and aggregate boundaries due to (i)compressive stress between the film and substrate because of a better matched coefficient of thermal expansion (CTE), and (ii) contamination of absorber layer with sodium (Na) diffused from SLG substrate. Various theoretical, chemical and simulation models are proposed to explain that Na acts as a catalyst in the absorber layer to passivate the Se vacancies and reduce the defect trap states, which directly influence and improve the efficiency and performance of the TFSC. The extent of this effect is further explored by depositing a NaF layer of various thicknesses on different substrates and concluded that performance is best at 0.14 at% Na diffusion through SLG. Influence of Li and K pre and post-deposition is found to enhance the performance of cells. Therefore, a glass substrate of a TFSC must have: (i) Glass transition temperature (Tg)gt 550°C (ii) presence of Na, K, Li (iii) CTE ~ 5-8×10-6 K-1 (iv) Low cost The present thesis describes the preparation of the alkali oxide containing calcium silicate glasses, wherein sodium oxide is systematically replaced by lithium and potassium oxide, via melt quench technique. The structural, optical, mechanical, thermal and electrical properties of the as-prepared glasses are studied using to determine their suitability as substrate for thin-film solar cells. The synthesized glasses were prepared as substrate to deposit Molybdenum thin film to study the diffusion of alkali ions from glass to Mo-film. The thesis is divided into six chapters with a list of cited references at the end of each chapter. Chapter 1 presents an introduction to glasses, its characteristic features, components of glasses and their effect on glass structure and their properties.