Design and Development of Thin Crystalline Silicon Solar Cell Employing Effective Light Trapping Schemes

In this thesis, the design and fabrication of PEDOT:PSS/c-Si hybrid heterojunction solar cells (HHSCs) were explored with a focus on achieving high efficiency and mechanical flexibility. The study investigated the integration of organic poly(3,4-ethylenedioxythiophene) (styrenesulfonate) (PEDOT:PSS) with ≤50 μm thin crystalline silicon (c-Si) wafers and various surface structuring techniques to enhance light absorption and device performance. Initially, methods for thinning commercially available thick Si wafers of thickness ~200 μm to ≤50 μm were developed, aiming to produce thin-flexible wafers for solar cell fabrication. These methods included mechanical grinding and chemical etching such as acidic and alkali. The resultant thin Si wafers exhibited enhanced flexibility and potential for cost reduction. In the next phase, the fabrication of PEDOT:PSS/n-Si hybrid solar cells on micro-pyramidal textured thin Si wafers was conducted. The micro-pyramidal texturing significantly reduced light reflection and enhanced light trapping, leading to the highest power conversion efficiency (PCE) of 10.42% in a simple device structure of ‘Ag/PEDOT:PSS/n-Si/In:Ga’. Subsequently, the integration of silicon nanowire (SiNW) texturing on thin-flexible Si wafers was investigated using a single-step silver-assisted chemical etching (Ag-ACE) process. The SiNW-incorporated solar cells demonstrated superior light absorption and charge generation due to enhanced light trapping, with optimal combinations of SiNW length (~170 nm) and PEDOT:PSS layer thickness (~100 nm) identified for the best performance. Additionally, silver nanoparticles (Ag NPs) were also incorporated into the PEDOT:PSS matrix to address challenges such as limited light absorption and charge transport in thin Si wafers to explore it potential avoiding surface micro/nano-structuring of thin Si wafers. The introduction of Ag NPs led to a significant enhancement (~21% relative) in the PCE of the hybrid device, attributed to improved light trapping and electrical conductivity of the polymer layer. Moreover, the thesis also explored the anti-reflection behaviour of periodic Si structures on thin Si wafers, specifically focusing on metal nanospheres (NSs) over periodic silicon nanopillar (Si NP) arrays. The effectiveness of light trapping by periodic Si NP via electron beam lithography (EBL) is also demonstrated. Finite-difference time-domain (FDTD) simulations were used to optimize these structures for maximum light harvesting and visualize the optical properties of the different structured Si surfaces. The research has demonstrated significant improvements in light trapping, charge transport, and overall device performance through innovative surface structuring and material integration. These findings have the potential to pave the way for the development of efficient, cost-effective, and flexible solar cells for diverse applications, from portable electronics to wearable technology, underscoring the importance of this work.