How does solar photovoltaic power generation convert sunlight into electricity?

I. The core principle of photovoltaic power generation: the magical journey from photons to electrons
(I) Semiconductor materials: the "energy converter" of photovoltaic power generation
The core of photovoltaic power generation is semiconductor silicon wafers. Its working principle is based on the photoelectric effect and needs to meet two key conditions:
Band gap matching: The band gap of silicon (Si) is 1.12 eV, which corresponds to the visible light (1.6-3.1 eV) and near-infrared light (0.7-1.6 eV) with the highest energy in the solar spectrum, and can effectively absorb about 40% of solar radiation energy;
PN structure: Through the doping process, P-type (boron doped, more holes) and N-type (phosphorus doped, more electrons) semiconductor interfaces are formed in the silicon wafer to form a built-in electric field (voltage of about 0.6-0.7V) to provide power for charge separation.
When sunlight shines on the silicon wafer, photons with energy greater than the band gap excite the valence band electrons to jump to the conduction band, generating electron-hole pairs. Under the action of the built-in electric field of the PN junction, electrons migrate to the N region and holes migrate to the P region, forming a potential difference. The external circuit can derive current and realize the direct conversion of light energy into electrical energy.
(II) Analysis of the key steps of photoelectric conversion
Photon absorption: The thickness of the silicon wafer is about 180-200μm, which can absorb more than 90% of the light with a wavelength of 400-1100nm, and the remaining energy is lost in the form of heat loss or transmission;
Charge separation: The built-in electric field of the PN junction makes the separation efficiency of electron-hole pairs reach more than 95%. If they are not separated in time, the charges will recombine and fail within 1-10 microseconds;
Current collection: The metal grid lines (spacing about 0.5-1mm) on the surface of the N region collect electrons, and the back electrode of the P region collects holes. A closed circuit is formed through the wire. The output voltage of a typical single cell is 0.5-0.6V, and the current increases linearly with the light intensity.
II. Key materials and structural design of photovoltaic cells
(I) Silicon wafers: from high-purity silicon to high-efficiency light-absorbing layers
Preparation of high-purity silicon: polycrystalline silicon ingots with a purity of 99.9999% are prepared by trichlorosilane reduction method (Siemens method), and then sliced and chamfered and ground to remove defects to form a light-absorbing core;
Surface texturing: using alkaline solution to etch the surface of silicon wafers to form a pyramid structure (height 1-10μm), reducing the light reflectivity from 30% to less than 5%, equivalent to increasing the light energy utilization rate by 15%;
Anti-reflection film coating: a 50-100nm thick silicon dioxide (SiO₂) or silicon nitride (SiNₓ) film is deposited on the surface of the silicon wafer to further reduce reflection through the principle of light interference, while protecting the silicon wafer from environmental erosion.
(II) Electrodes and conductive materials: Let the charge "run"
Metal grid lines: The grid lines printed with silver paste on the front side (width 20-30μm) need to balance conductivity and shading rate. Optimized design can make the shading area <5% and the current collection efficiency > 98%;
Back contact technology: Placing all positive and negative electrodes on the back of the battery (such as IBC batteries) to avoid shading of the front grid lines, the conversion efficiency can be increased by 1-2%. A laboratory has achieved 26.8% efficiency of single-crystal silicon batteries;
Role of auxiliary materials: In some conductive pastes or interface layers, manganese dioxide (MnO₂) can be used as a conductivity enhancer or catalyst to increase the charge transfer rate through its unique layered structure, or as a hole transport layer modification material in perovskite batteries. Although it is not the core, it helps to optimize performance.
III. From single cell to power generation system: technical advantages and application scenarios
(I) Three-layer architecture of photovoltaic system
Battery layer: single silicon cells are connected in series to form a module (60/72 pieces in series, voltage 30-40V), which is encapsulated by EVA film and glass/backplane, with a weather resistance of 25 years (power attenuation < 20%);
Inverter layer: converts DC power into AC power (conversion efficiency > 98%), and has MPPT (maximum power point tracking) function to optimize output power in real time. According to actual measurements, a certain project can increase power generation by 5-8%;
System layer: cooperate with brackets (tracking/fixed), junction boxes, and monitoring equipment to form a complete power generation unit. Distributed photovoltaic (home/industrial and commercial) and centralized power stations (desert/water surface) each have their own advantages.
(II) Irreplaceable environmental and economic advantages
Clean properties: The annual power generation of each kilowatt of photovoltaic installed capacity is 1200-1500kWh, which is equivalent to reducing CO₂ emissions by 1 ton, and reducing emissions by 25 tons within the life cycle (25 years), which is more than 5 times the carbon emissions in the manufacturing process ("energy payback period" <1.5 years);
Cost advantage: In the past ten years, the cost of photovoltaic electricity has dropped from 3 yuan to less than 0.3 yuan, which is lower than coal-fired power generation (0.5 yuan). The investment payback period of a certain industrial and commercial rooftop project has been shortened to 5-6 years;
Application resilience: Stable operation in an environment of -40℃ to 85℃, the installed capacity in Tibet's high-altitude areas (light intensity 1800kWh/m²/year) has increased by 20% annually, becoming the first choice for power supply in remote areas.
IV. Technology iteration: From polysilicon to the breakthrough of next-generation photovoltaics
(I) Three major directions of efficiency improvement
Structural innovation: HIT cells (heterojunction) passivate the amorphous silicon/crystalline silicon interface, with a conversion efficiency of 26.8% (> 24% for mass production line), and a temperature coefficient as low as -0.25%/℃, which is more adaptable to high temperature environments than traditional PERC cells (-0.38%/℃);
Material expansion: The laboratory efficiency of perovskite cells reaches 26.3%, and the efficiency of silicon-based stacked cells exceeds 33%. Its adjustable bandgap characteristics (1.2-2.3eV) can cover a wider spectrum, and may become the "efficiency ceiling" in the future;
Process optimization: TOPCon cells improve the carrier separation efficiency through the back tunneling oxide layer (1-2nm SiO₂), and the mass production efficiency exceeds 25%. A manufacturer has planned a 100GW production capacity, pushing the industry into the "25% efficiency era".
(II) Potential auxiliary value of manganese dioxide
In the research of new batteries, the application of manganese dioxide is gradually emerging:
Conductive agent modification: Adding MnO₂ nanosheets to the carbon electrode of perovskite battery can increase the electron transfer rate by 15% and reduce the interface resistance;
Catalyst function: In the photovoltaic water electrolysis hydrogen production system, MnO₂ is used as an oxygen evolution catalyst (OER) to achieve efficient hydrogen production with photovoltaic power. Although it is not the core of photovoltaics, it has expanded the "light-electricity-hydrogen" industry chain.
V. Challenges and the future: Let the sun illuminate every kilowatt-hour of electricity
Silicon material bottleneck: Polysilicon production consumes a lot of energy (120-150kWh per kilogram of electricity), and it is necessary to promote the fluidized bed method (energy consumption reduced by 50%) and electronic-grade silicon recycling technology (recovery rate > 90%);
Energy storage support: Photovoltaic output is affected by day and night, and it is necessary to simultaneously develop lithium batteries (energy storage efficiency 90%) and pumped storage (capacity up to GW level) to achieve the leap from "generating and using" to "stable power supply";
Policy support: More than 130 countries in the world have proposed carbon neutrality goals, and China's "whole-county promotion" distributed photovoltaic policy is expected to drive the installed capacity to exceed 100 million kilowatts in 2025, with a market size of 30% annually.
Conclusion
From the first practical silicon cell (6% efficiency) at Bell Labs in 1954 to today's 26%+ efficient modules, solar photovoltaic power generation has taken 70 years to prove that breakthroughs in scientific principles can transform natural gifts into a force that changes the energy landscape. When sunlight shines on silicon wafers and electrons migrate in an orderly manner in PN junctions, this technology based on semiconductor physics not only lights up thousands of homes, but also illuminates the only way for humans to bid farewell to fossil energy. With the continuous advancement of material innovation and system integration, solar photovoltaic power generation will become the "cheapest and most reliable" energy option, making every kilowatt-hour of electricity shine with clean light.

author: Hazel
date:2025-05-28