Photovoltaic Cells: What They Are and How They Work

Photovoltaic cells, semiconductor devices capable of transforming sunlight into electrical energy thanks to the photovoltaic effect, represent the fundamental unit of every photovoltaic system.

A photovoltaic plant is characterized by a set of solar panels, arranged in series or in parallel; at the base of each panel are the photovoltaic cells, responsible for converting solar radiation into electricity.

Let’s discover together what the basic elements of a photovoltaic system are and how they work.

The design of a photovoltaic system is a very delicate operation that requires particular care and attention. To avoid making mistakes that could cost you dearly after the installation of the system, I recommend relying on an effective photovoltaic software to design systems safely and guided.

What are photovoltaic cells?

Photovoltaic cells are the basic element in the production of electricity through solar energy. They can be made from different materials, but the most widespread and effective semiconductor is silicon.

Silicon has an important characteristic: only a minimal amount of energy is needed for valence electrons to be harnessed to generate an electric current.

To exploit this phenomenon, the so-called doping is used, which involves the introduction of impurities into the semiconductor. Usually, boron (negative charge) and phosphorus (positive charge) are used, which create a barrier known as the junction zone. It is thanks to this p-n junction that the diode is formed, an essential element for transforming sunlight into usable electrical energy.

Tetravalent silicon doping

Operation of a photovoltaic cell

To verify the efficiency of a photovoltaic cell, it is necessary to connect it to two measuring instruments, namely the ammeter, which measures electric current, and the voltmeter, which measures voltage.

In an electrical circuit, the two instruments are connected in parallel to prevent the ammeter from measuring the electrical resistance present within the voltmeter itself and to ensure the measurement of the cell’s performance independently of external systems.

Photovoltaic cell – electrical measurements

Inside the circuit, an electric load is also inserted, which affects the performance of the cell: depending on the load, both the intensity and the voltage of the produced current vary. In these conditions, two main cases are distinguished:

• open circuit: the current is zero (no electrical contact), while the voltage reaches the maximum value that the cell can produce (Voc – open circuit voltage);
• closed circuit: the load is minimum and the current is maximum (Isc – short circuit current), while the voltage is close to zero.

The graphical representation of these values generates the V-I characteristic curve (or volt-ampere curve), from which fundamental parameters such as:

• peak intensity;
• peak voltage;
• peak power;
• fill factor.

Another very important parameter is the maximum power point (MPP), which represents the optimal working condition of the cell. In real systems, the task of continuously tracking this point is entrusted to inverters equipped with MPPT technology (Maximum Power Point Tracking).

Distinguishing factors of a photovoltaic cell

Structure and Materials of a Photovoltaic Cell

A photovoltaic cell is composed of multiple layers of materials that, together, allow for the conversion of sunlight into electrical energy:

• front transparent layer: usually tempered glass, protects the cell from environmental agents and lets solar radiation pass through;
• anti-reflective layer: reduces light dispersion, maximizing absorption;
• semiconductor layer: generally silicon, is the heart of the cell. Here the photovoltaic effect occurs thanks to the p-n junction created by doping;
• metal contacts: thin conductive grids deposited on the front and back surfaces, which collect the electrons generating electric current;
• back layer: often made of plastic or metal materials, provides insulation and mechanical protection.

In recent years, new materials such as perovskites have also been developed, which promise to increase efficiency and reduce costs, although they are still in the research and experimentation phase.

Types of Photovoltaic Cells and Their Characteristics

Photovoltaic cells are mainly distinguished based on the structure of silicon with which they are made. The most common types are:

• monocrystalline cells;
• polycrystalline cells;
• amorphous cells.

Types of photovoltaic cells

Monocrystalline photovoltaic cells

Monocrystalline cells are made from a single crystal, oriented in the same direction. This characteristic allows for the optimal utilization of solar energy that the cell is capable of capturing. The color of these cells is typically black.

The method used to produce monocrystalline cells is the Czochralski process. This is a process in which a crystal seed is inserted into a molten silicon, within which the seed rotates vertically counterclockwise and, by slowly dipping, allows the molten silicon to crystallize orderly onto the immersing seed.

Monocrystalline photovoltaic cells

At the end of the process, all the crystals are oriented uniformly enough to materialize a single macro crystal, giving rise to a silicon ingot.

The ingot is then sliced into thin wafers, just a few hundred micrometers thick: the thinner the wafer, the greater the efficiency of the photovoltaic cell. Finally, the wafers are appropriately doped (with boron or phosphorus) and assembled to form the photovoltaic cells.

These cells are the most efficient (15–22%) and have a long lifespan, but also higher production costs.

Monocrystalline silicon bar

Polycrystalline photovoltaic cells

Polycrystalline cells are derived from waste from the electronics industry; they are formed from multiple crystals and their typical coloration is that of shimmering blue.

Polycrystalline cells

Cooling occurs more quickly compared to monocrystalline, in a thermostatic bath that crystallizes silicon in different directions. This allows for a faster and more economical production process, but with slightly lower efficiency (12-18%), due to the disordered orientation of the crystals.

They are very common because they offer a good compromise between price and performance.

Detail of polycrystalline cell

Amorphous Photovoltaic Cells (Thin Film)

The amorphous photovoltaic cells have a more chaotic structure than silicon, which, in this configuration, no longer has a crystalline form.

This characteristic allows for the creation of thin film cells, extremely thin and flexible, which can also be applied to surfaces that are not perfectly flat.

The process of creating an amorphous cell is very simple: on a rigid substrate (glass or metal), multiple layers of material are deposited using appropriate technologies (sputtering or evaporation), two of these layers (the outermost) become conduction electrodes, while the inner layer becomes the junction of the photovoltaic cell.

In this process, the technologies mainly used are triple junction technology and cadmium-telluride/cadmium-sulfide (CTS) technology.

Amorphous cells have lower efficiency (6–12%) and shorter lifespan, but they are very versatile and find applications in architectural integration (facades, curved roofs, urban furniture) and in portable devices.

To explore the differences between various technologies, you can also check out this article on types of photovoltaic systems.

Amorphous photovoltaic cell

Series and Parallel Configurations in Photovoltaic Modules

Photovoltaic cells are diodes and behave like batteries. They can be connected in series or in parallel.

• In a series connection (positive to negative), voltages add up and current remains constant. The characteristic curve shows an increase on the voltage axis.
• In a parallel connection (positives with positives and negatives with negatives), voltage remains constant while current increases. In this case, the curve shifts upward.

In addition to configurations, environmental conditions also affect cell performance:

• temperature: if temperature rises beyond certain values, voltage decreases, leading to a loss of efficiency. This is one of the reasons why photovoltaic modules are tested with temperature coefficients declared by manufacturers;
• solar radiation: as irradiation decreases, current intensity significantly reduces while voltage varies little; thus, the curve tends to flatten.

To correctly design a system, it is essential to rely on reliable climatic data, such as that provided by solar atlases or field measurement campaigns. In this context, photovoltaic design software is extremely useful, allowing the calculation of expected production taking into account actual solar irradiation, available in the main international meteorological databases.

From a Single Cell to the Solar Module: How Panels are Built

Photovoltaic cells connect to each other to form photovoltaic panels, which, in turn, connect to each other forming the photovoltaic system.

Each panel consists of dozens of electrically connected cells in series and is enclosed in a structure made of protective glass, encapsulating layers, and aluminum frames, ensuring mechanical strength and durability over time.

In such a connection, panels can be arranged in different strings, possibly connected in parallel with each other. This configuration allows obtaining the necessary voltage and current to meet project requirements.

Once the power to install is determined, it is possible to decide to produce it with a variable number of panels. The choice depends on several factors:

• available solar radiation in the installation area;
• orientation and tilt of the modules;
• available space and architectural constraints.

PV cells: configuration of 2 strings of 3 modules

PV cells: configuration of 3 strings of 2 modules

How Photovoltaic Cells Generate Electricity from Sunlight

The operation of photovoltaic cells is based on the so-called photovoltaic effect, a physical phenomenon discovered in the nineteenth century and now exploited to produce clean electrical energy.

When sunlight hits the silicon layer of the cell, photons transmit their energy to the electrons present in the semiconductor. This energy is sufficient to free the electrons from their atomic bonds, allowing them to move.

The presence of the p-n junction, created through doping, causes the free electrons to be directed towards one side of the cell, while the holes (positive charges) move towards the other. This movement generates a potential difference between the two layers.

By connecting metallic contacts to an external circuit, electrons can flow: thus, direct current is born.

In a real photovoltaic system, the current produced by the cells is then channeled and converted by the inverter into alternating current, compatible with the electrical grid and with domestic or industrial uses.

The efficiency with which the cell converts solar radiation into electricity depends on various factors: material quality, thickness of the semiconductor, operating temperature, and light intensity. Tools like the solar diagram help designers study the available irradiation and optimally position the panels to maximize production.

Advantages and Disadvantages of Photovoltaic Cells

Photovoltaic cells are today one of the most widespread technologies for the production of renewable energy, thanks to the numerous benefits they offer. However, they also have some limitations that are important to consider in the design and installation phase.

Advantages

• clean and sustainable energy: they do not produce polluting emissions during operation and contribute to the reduction of greenhouse gases;
• economic savings over time: the initial investment is repaid through savings on the bill and, in some cases, with incentives and tax deductions;
• low maintenance: photovoltaic cells have no moving parts and only require periodic cleaning and routine checks;
• scalability: it is possible to install a few modules for small needs or large systems to generate energy on a large scale;
• architectural integration: with thin-film or flexible technologies, the modules can be integrated into facades, roofs, and even urban design elements.

Disadvantages

• dependence on solar radiation: energy production varies according to weather conditions and available irradiation;
• initial cost: although constantly decreasing, the initial investment can be significant, especially for large systems;
• limited efficiency: current cells convert only a portion of the incident solar radiation into electricity (an average of 15–22% for crystalline silicon modules);
• degradation over time: performance gradually decreases with the age of the modules, although manufacturers usually guarantee at least 80% power after 20–25 years;
• waste disposal and recycling: end-of-life panels contain materials that must be recovered and disposed of correctly, a challenge still evolving.

Flexible Photovoltaic Cells and New Technologies

Alongside traditional crystalline silicon solutions, new generations of photovoltaic cells have developed in recent years, with innovative characteristics and increasingly versatile applications.

Flexible Photovoltaic Cells

These cells use thin and lightweight materials, such as amorphous silicon or alternative semiconductor compounds (e.g., cadmium telluride or copper-indium-gallium selenide, CIGS). Their main feature is flexibility, making them suitable for:

• curved or irregular surfaces;
• mobile applications (tents, campers, boats, portable devices);
• innovative architectural integration, such as lightweight coverings or transparent facades.

They still have lower efficiency compared to crystalline silicon cells, but research aims to improve their performance and durability.

Next-Generation Cells

In addition to flexible cells, research is exploring new technologies:

• perovskite cells: cost-effective materials, easy to produce, and with very high potential efficiency (>25%). They are currently experimental due to stability and durability issues;
• tandem cells: combining multiple materials (e.g., perovskite + silicon) to capture different wavelengths of sunlight, thereby increasing efficiency;
• organic cells (OPV): made with conductive polymers, lightweight and potentially printable, ideal for design applications and electronic devices.

These innovations pave the way for a future where solar panels are not just standardized elements, but integrable components in any surface or technological product.

How to Optimize the Design of a Photovoltaic System

The design of a photovoltaic system is not limited to the choice of cells or panels: it requires a careful study of the climatic conditions, orientation, tilt, and the energy needs of the building or system.

In this context, photovoltaic design software becomes a fundamental tool. They allow you to:

• calculate the expected energy production based on actual irradiation data;
• simulate different configurations for the orientation and tilt of the modules;
• identify the impact of any shading;
• correctly size inverters and storage systems;
• evaluate the economic feasibility of the intervention.

The use of photovoltaic software is not just a technical support, but also an ally for making more informed decisions, reducing margins of error, and creating truly efficient and sustainable systems. For professionals, this means being able to design customized, reliable, and high-performance solutions. With professional photovoltaic software, you can design easily and quickly, optimize system performance, reduce costs, and offer your clients reliable and competitive solutions for the energy transition. Furthermore, such software has specific libraries of modules, inverters, batteries, and photovoltaic components, essential for correct design.

FAQ – Photovoltaic Cells

What is a photovoltaic cell?

A photovoltaic cell is a semiconductor device that converts solar radiation into electrical energy by exploiting the photovoltaic effect. It represents the fundamental unit of solar panels and is the basic element of any photovoltaic system.

How do photovoltaic cells work?

The operation of photovoltaic cells is based on the photovoltaic effect. When sunlight strikes the silicon in the cell, photons transfer energy to the semiconductor’s electrons, freeing them from atomic bonds. The presence of the p-n junction, created through silicon doping, generates a potential difference that sets the electrons in motion. By connecting the metal contacts to an external circuit, direct current (DC) electricity is produced.

What are the main types of photovoltaic cells?

Photovoltaic cells are primarily classified according to the structure of the silicon used. The most common types are:

• monocrystalline cells, made from a single silicon crystal;
• polycrystalline cells, composed of multiple crystals;
• amorphous or thin-film cells, characterized by a non-crystalline structure and greater flexibility.

These technologies exhibit different characteristics in terms of efficiency, cost, and applications.

What is the efficiency of photovoltaic cells?

The efficiency of photovoltaic cells indicates their ability to convert solar radiation into electrical energy. This value depends on several factors, including material quality, semiconductor thickness, operating temperature, and solar irradiance.

The most widely used technologies have different efficiency ranges:

• monocrystalline cells: 15–22%
• polycrystalline cells: 12–18%
• thin-film cells: 6–12%

Monocrystalline cells are generally the most efficient, while thin-film cells have lower efficiencies but offer greater flexibility and application versatility.

What is the difference between a photovoltaic cell and a photovoltaic panel?

A photovoltaic cell is the individual semiconductor device that generates electrical energy from sunlight. A photovoltaic panel, or module, is composed of multiple cells electrically connected to one another and encapsulated within a protective structure consisting of glass, encapsulant layers, and an aluminum frame. Multiple interconnected panels form a photovoltaic system.

How are photovoltaic cells interconnected?

Photovoltaic cells can be connected in series or in parallel. In a series configuration, voltages add up while the current remains constant. In a parallel configuration, the voltage remains constant while the current increases.
These configurations make it possible to achieve the voltage and current levels required for the operation of photovoltaic modules and systems.

What factors affect the performance of photovoltaic cells?

The performance of photovoltaic cells is mainly influenced by:

• temperature, which can reduce voltage and therefore cell efficiency;
• solar irradiance, which directly affects the generated current;
• the quality of semiconductor materials and the cell structure.

For this reason, when designing a photovoltaic system, it is important to consider reliable climatic data and use simulation tools to estimate energy production.