How photons excite electrons in silicon
Solar electricity begins with an extraordinary microscopic event: a packet of light transfers enough energy to free an electron from its bond inside silicon. That electron can then become part of an electric current. Repeating this process across billions of atoms produces useful power without combustion, moving parts or direct carbon emissions at the point of generation.
Understanding this quantum behaviour helps explain panel efficiency, temperature losses, inverter performance and the value of a solar installation. It also reveals why wavelength, semiconductor structure and the junction between materials matter as much as the amount of sunlight reaching the roof.
From sunlight to an electric current
Light can be described as photons, each carrying a precise amount of energy. When a photon enters silicon and is absorbed, its energy can promote an electron from the material’s valence band into its conduction band. The electron is then free to move through the crystal, while the space it leaves behind is called a hole.
A hole behaves as if it carries positive charge. In an ideal photovoltaic process, photons generate electron-hole pairs, but their presence alone does not guarantee electricity. The pairs must be separated and directed toward opposite contacts before they recombine and lose their energy as heat or light.
A solar cell creates that separation through carefully engineered layers. Its p-type and n-type regions form a junction with a built-in electric field. The field acts like a microscopic sorting mechanism, sending electrons toward one electrode and holes toward the other. This charge separation creates the voltage and current measured at the panel terminals.
Why the wavelength of light matters
The energy of a photon is expressed as (E = hc/\lambda), where (h) is Planck’s constant, (c) is the speed of light and (\lambda) is wavelength. Shorter wavelengths therefore carry more energy than longer wavelengths.
Silicon has a band gap of about 1.12 electronvolts at room temperature. A photon with at least this much energy can usually generate an electron-hole pair. A longer-wavelength infrared photon may pass through the cell or be weakly absorbed because it lacks sufficient energy, while visible and shorter-wavelength photons are strongly absorbed when their energy exceeds the gap.
Much of the energy in visible sunlight is greater than silicon’s band gap. The surplus cannot become additional electrical voltage in a single-junction cell; instead, it is converted into heat through carrier relaxation. Specialist resources offering photonic modelling services can support research into semiconductor materials, optical absorption and ways to reduce these losses.
The junction that separates charge
Pure silicon has four valence electrons that form covalent bonds with neighbouring atoms. Adding a small amount of phosphorus creates n-type silicon with extra electrons, while adding boron produces p-type silicon with holes as the majority carriers. Bringing these layers together forms the p-n junction at the heart of a conventional solar cell.
The junction’s built-in field sweeps carriers that diffuse into its depletion region. Electrons move toward the n-type layer and holes toward the p-type layer. Under illumination, this movement produces photocurrent, while the separation of charge establishes a voltage between the cell’s terminals.
Individual cells produce relatively little power, so manufacturers connect them in series to raise voltage and in parallel to increase current. The resulting module supplies direct current, which an inverter converts into alternating current for household or commercial use. SMA inverters also apply maximum power point tracking to adjust for changing irradiance, temperature and electrical operating conditions.
Comparing silicon with other photovoltaic materials
Crystalline silicon is the dominant material in most Australian installations, but its band gap limits how efficiently it can use the full solar spectrum. Other technologies use different absorbing layers or multiple junctions to capture light across a broader range of wavelengths.
| Photovoltaic material | Typical light response | Main strengths | Main limitations |
|---|---|---|---|
| Crystalline silicon | Single junction with a band gap near 1.12 eV | Mature manufacturing, extensive operating history and a well-established inverter ecosystem | Energy-intensive production and excess energy lost as heat in a single junction |
| Thin-film CdTe or CIGS | Lower or adjustable band gap with strong absorption | Thin active layers, flexible formats and useful performance in heat | Smaller supplier base and material-specific recycling requirements |
| Perovskite-silicon tandem | Upper and lower cells capture different portions of the spectrum | Higher potential efficiency because less solar energy becomes heat | Long-term stability, encapsulation, bankability and recycling remain development priorities |
| Emerging quantum-dot and organic cells | Tailorable optical properties at very small scales | Potential for lightweight devices or specialised applications | Low durability, consistency and commercial scale currently limit adoption |
A tandem device can place a wide-band-gap upper cell above silicon. The upper cell absorbs higher-energy photons, while silicon uses lower-energy photons that pass through it. This reduces thermal losses and can raise laboratory efficiency beyond that of either material alone.
Practical selection still depends on more than theoretical efficiency. Manufacturing maturity, product availability, warranties, system balance, fire safety, electrical standards and end-of-life arrangements all affect bankability. Silicon’s advantages therefore extend beyond its absorption characteristics, particularly in the established residential and commercial markets.
Losses that limit real-world output
A panel’s nameplate rating is measured under standardised laboratory conditions. Actual output is lower because some light is reflected or absorbed without producing a usable carrier. Other losses arise from electrical resistance, imperfect contacts, recombination and differences between the cell and its protective encapsulation.
Heat is especially important in Australia. The current-voltage relationship of silicon shifts as a cell becomes warmer, reducing maximum power even though sunlight remains intense. Consequently, a Brisbane or Sydney installation may produce less on a hot summer afternoon than the same system would on a cooler, bright day. Keeping the rear ventilation space clear helps the modules shed heat.
Australia also presents widely different operating conditions. Melbourne experiences frequent frontal changes and broken cloud, while Perth and Adelaide enjoy abundant clear-sky irradiation. Coastal salt, inland dust, leaves and bird droppings can reduce performance locally. Regular inspection, appropriate cleaning intervals and reliable monitoring help maintain output as weather, shade and operating conditions change.
Build an Australian solar plan with confidence
In the Southern Hemisphere, north-facing roofs generally receive more useful winter sunlight than south-facing roofs. Roof pitch, nearby shading, window layouts and roof construction should be assessed for the actual property. Sydney, Adelaide, Brisbane and Melbourne each have distinct irradiance patterns, so regional weather data is more informative than a generic national average.
Australian household systems normally deliver 230-volt, 50-hertz alternating current, although commercial arrangements may use three-phase power. Installations must satisfy applicable electrical and grid-connection requirements and receive approval from the relevant network operator. Using an appropriately accredited installer and an accredited designer can reduce technical and administrative risks.
The federal Small-scale Technology Certificates scheme, administered by the Clean Energy Regulator, can affect project economics when a system is eligible. State programs and local incentives may also apply, with rules and availability changing over time. Compare the full system quotation, inverter specifications, warranty, monitoring and expected savings rather than focusing only on panel wattage or a headline rebate.
Begin by reviewing your roof, electricity usage, shading and equipment requirements against those local conditions. Solar Is Future’s common solar questions provide useful background while you prepare for a site-specific assessment, then request a written proposal showing the proposed system, expected output, costs, approvals and payback assumptions.