POTENTIAL APPLICATION OF 2D CARBON MATERIALS IN SILICON HETEROJUNCTION SOLAR CELLS

Abstract

As the world moves toward more sustainable energy systems, photovoltaic technologies are becoming vital in supplying the increasing electricity demand. Silicon-based solar cells remain the most popular among PV technologies because of their advanced technology, scalability, high efficiency, and long-term dependability. Nevertheless, in order to address the challenges of mounting worldwide energy consumption and the limitations imposed within conventional device structures, further power conversion efficiency advancement is anticipated. In this regard, the integration of two-dimensional materials with silicon-based heterojunction solar cells represents a promising strategy to transcend existing performance barriers. In this thesis, AFORS-HET simulation software is used. to numerically investigate the feasibility of the integration of diamane, a recently synthesized 2D diamond-like allotrope of carbon, into silicon-based solar cell designs. Diamane is reported to be a promising material for advanced photovoltaic applications because of its wide and tunable bandgap, excellent optical properties, and higher carrier mobility. The objective of this thesis is to meticulously investigate the integration of doped diamane as a promising material to be used as the emitter and back surface field (BSF) layers in silicon-based heterojunction solar cells. The application of n-type diamane as an emitter layer in an ITO/n-Diamane/p-cSi/Ag heterostructure solar cell is investigated in the first section of the study. A maximum power conversion efficiency (PCE) of 16.84% was attained at 300 K by layer’s parameter optimization. To validate its practical applicability, the structure was simulated using commercially available silicon substrates that are commercially accessible, resulting in an efficiency of 10.41%. The analysis also revealed that as the diamane thickness increased, efficiency slightly decreased, highlighting the importance of precise thickness control. After that, an advanced HIT structure, Gr/n-Dn/a-Si: H(i)/p- c-Si/Ag, is modelled. Here, graphene with zero absorption loss is used as the transparent conducting oxide (TCO). The optimized cell delivered a record efficiency of 31.2%, surpassing structures that utilized traditional ITO electrodes. The results highlight their vi unique compatibility and practical synergy by demonstrating that the Gr/Dn interface of carbon materials could serve as both an emitter and a TCO, respectively. In order to further enhance device performance, doped diamane was used as an efficient electron/hole collection layer. The modelled structure is Gr/n-Dn/a-Si: H(i)/p-c-Si/p- Dn/Au. Specifically, the n-type and p-type diamane layers are used as the emitter and BSF layers of the cell, respectively. For the fully optimized configuration, which accounts for absorption losses at the front contact, a conversion efficiency of 27.88% is achieved, with a short-circuit current density (JSC) of 49.3 mA/cm², open-circuit voltage (VOC) of 691.1 mV, and fill factor (FF) of 81.83%. A comprehensive analysis is also conducted on the influence of front surface texturing angle and associated optical losses, providing insights into light exposure angle to enhance photovoltaic performance. The study further presents a detailed simulation of BSFHJ and BSFHIT solar cells, incorporating passivation strategies and precise control over material bandgaps and thicknesses. The simulated structures, Gr/n-Dn/p-c-Si/p-Dn/Au and Gr/n-Dn/a-Si: H(i)/p-c-Si/a-Si: H(i)/p-Dn/Au, achieved efficiencies of 26.86% and 29.38%, respectively. For the BSFHJ cell, optimal performance was obtained with an n-diamane emitter (thickness 1.36 nm, bandgap 1.4 eV) and a p-diamane BSF layer (2.04 nm, 1.6 eV). In contrast, the BSFHIT structure reached optimum efficiency using much thinner diamane layers (0.34 nm), with band gaps of 1.6 eV (n-type) and 1.3 eV (p-type). The ideal c-Si thickness was found to be 80 μm for BSFHJ and 35 μm for BSFHIT, indicating potential for material savings and enhanced sustainability, albeit with associated fabrication challenges for ultra-thin wafers. Key performance parameters, including VOC, JSC, FF, J–V characteristics, and spectral response, were analyzed in detail, confirming that the integration of both passivation and BSF layers substantially improves device efficiency. Finally, we explored a cell design with SiO₂/Si₃N₄ passivation layers on the emitter layer, resulting in the structure Gr/Si₃N₄/SiO₂/n-Dn/p-c-Si/p-Dn/Au. A high current density of 54.53 mA/cm² and an efficiency of 30.59% were attained in this optimized design. To illustrate the superior effectiveness of diamane-based structured solar cells, a traditional PERC structure with a-Si for both emitter and BSF layers was also simulated, which yielded an efficiency of 24.01%. In order to further identify the most efficient design, a vii comparison study of each simulated configuration was carried out. Among these structures, the passivated emitter layer BSFHIT structure was found to be more efficient, with the highest efficiency of 30.69%. This confirms the practical utility and commercial significance of the proposed 2D carbon material-based solar cells. In summary, the present work confirms that doped diamane is a multifunctional material for high-efficiency silicon photovoltaics. The possibility of developing a new class of carbon-integrated solar cell design is being offered. This happened as a result of graphene's ability to work as a transparent conducting electrode and diamene's dual use as an emitter and BSF layer. These findings pave the way towards the development of high-performance, sustainable solar systems based on 2D carbon materials, providing a strong theoretical basis for future demonstrations and commercial applications.