A photovoltaic solar cell, also known as a solar cell, is a device that converts sunlight directly into electricity. It utilizes the photovoltaic effect, which is a phenomenon where light photons excite electrons in a material, causing them to flow and generate electricity. Solar cells are the fundamental building blocks of photovoltaic modules, commonly referred to as solar panels.

The majority of photovoltaic modules on the market today are made from crystalline silicon, holding a market share of around 95%. However, there are also thin-film solar cells that use cadmium telluride (CdTe) as the raw material.

Structure and Materials of a Photovoltaic Module

While there are various solutions and materials available, the basic structure of a solar panel follows a common philosophy across manufacturers. Here's a breakdown of the key components and their materials:

• Photovoltaic cells: These are the heart of the panel, responsible for capturing sunlight and converting it into electricity. They can be monocrystalline or polycrystalline based on the manufacturing process, but this doesn't significantly impact the module production itself. Key characteristics to consider include size, color, number of electrical conductors (bus-bars), and most importantly, conversion efficiency. Conversion efficiency directly affects the power output of the panel. Currently, polycrystalline cells are the most common with an efficiency of around 17.6%, translating to a 250-watt photovoltaic module with 60 cells. These cells are interconnected using thin copper tapes coated with a tin alloy, called ribbons.

• Front glass: This is the heaviest component, providing protection, structural integrity, and high transparency for sunlight penetration. The thickness typically ranges from 2mm to 4mm depending on the chosen glass type. Important features to consider are hardening quality, spectral transmittance (light wavelengths allowed to pass through), and light transmittance (overall amount of light passing through). Specialized glasses with textured surfaces for better light trapping are also available. Careful selection and additional anti-reflective coatings can improve overall module efficiency.

• Backsheet: As the name suggests, this is a plastic sheet on the back of the module. It electrically isolates, protects, and shields the solar cells from environmental factors like moisture. Backsheets are typically white and come in rolls or sheets. Variations exist in thickness, color, and the inclusion of specific materials for enhanced shielding or mechanical strength.

• Encapsulant material: This material acts as a binding agent between the various layers within the solar panel. Ethylene vinyl acetate (EVA) is the most common encapsulant, a translucent polymer applied in sheets before and after the photovoltaic cells. During a vacuum lamination process, EVA transforms into a transparent gel, effectively embedding the solar cells. The quality of this lamination process significantly impacts the module's lifespan, while the encapsulant itself affects light transmission, processing speed, and resistance to yellowing from UV rays.

• Frame: Typically made of aluminum, the frame provides structural robustness and facilitates secure mounting of the photovoltaic module. A layer of sealant is applied around the edges of the panel along with the frame to prevent moisture ingress. Silicon is the most widely used sealant, although special sealing tapes can also be employed. Frameless modules or those with special plastic backsheet solutions are available for specific applications. These often involve glued-on rear supports or glass-on-glass technology.

• Junction box: This external box houses the electrical connections of the photovoltaic module. It contains bypass diodes for shade management and cables for connecting multiple panels in a solar array. Key factors to consider when choosing a junction box include the quality of plastic used, sealing effectiveness, type of ribbon connection, and the quality of bypass diodes. Recent advancements include junction boxes with special low-loss diodes or integrated micro-inverters, although their widespread adoption is limited by cost.