Detailed explanation of working principle of silicon solar cell

The introduction to the silicon solar battery

Si Si, atomic number 14, atomic weight of 28.0855, with crystalline and amorphous silicon in two forms.Solar energy is inexhaustible renewable energy.Is clean energy, not cause any environmental pollution.

In the effective use of solar energy;Solar photovoltaic utilization is the fastest growing in recent years, the most active research areas, is one of the most high-profile projects.

Silicon solar cell classification

Production of solar cells is based mainly on semiconductor materials, its working principle is to use the photoelectric photoelectric conversion reaction, in the aftermath of the material to absorb light energy according to different materials, the solar cell can be divided into:

1, silicon solar cell;

2, inorganic salts, such as gallium arsenide III -v compound, cadmium sulfide, copper indium selenium diverse compounds for materials such as battery;

3, solar cells of the preparation of functional polymer materials;

4, nanocrystalline solar cells, etc.

A, silicon solar cells

1.Silicon solar cells work principle and structure

The principle of the solar cell power generation is mainly semiconductor photoelectric effect, general semiconductor main structure is as follows:

Silicon material is a kind of semiconductor material, the principle of the solar cell power generation is mainly the use of the semiconductor photoelectric effect.Generally the molecular structure of the semiconductor is like this:

Said said of the silicon atoms, negative charge around four electronic next to the silicon atoms.

When mixed with other impurities in silicon crystal, such as boron (silver or black solid, melting point 2300 ℃, boiling point 3658 ℃, the density of 2.34 g/cm, hardness is second only to diamond, relatively stable at room temperature, with nitrogen, carbon, silicon, high temperature boron also react with many metals and metal oxides, metal boride.These compounds are usually high hardness, refractory, high electrical conductivity and chemical inertness of the material.)Phosphorus, etc., when mixed with boron, silicon crystal will there is a hole in the formation of it can refer to below details:

Said said of the silicon atoms, negative charge around four electronic beside the silicon atoms, and yellow said adding boron atoms, only three electrons around because of boron atoms, so can produce as shown in the blue hole, the hole because there is no electronic and become very unstable, and easy to absorb electrons, forming P type semiconductor,).

, what is a p-type semiconductor (with?In semiconductor material silicon or germanium crystals doped triad impurities may constitute a lack of shell grain of p-type semiconductor, impurities mixed with price of five elements can form redundant shell grain of n-type semiconductor.)

Similarly, adding phosphorus atoms, because phosphorus atoms are five electrons, so there will be an electronic become very active, formation of N type semiconductor (negative).Yellow phosphorus nuclei, red for the excess electrons,

P type semiconductor contains more holes, and the n-type semiconductor contains more electrons, so that when the p-type and n-type semiconductor together will form in contact potential difference, this is PN junction.

When the p-type and n-type semiconductor together in two kinds of semiconductor interface area will form a special thin layer, the p-type side of the interface are negatively charged and positively charged N side.This is because the p-type semiconductor hole, n-type semiconductor more free electrons, the concentration difference.P the hole will be spontaneous diffusion area to N, N the electron will spontaneously spread to P area, as a result of the electrons and holes, the original rendering neutral enrichment of p-type semiconductor near the interface is negative charge (as part of the hole diffusion to the N area), similar to the original rendering neutral enrichment of n-type semiconductor near the interface is a positive charge (as part of the electron diffusion to P area), forming a N to P "inside the electric field", so as to prevent the spread of electrons and holes.Reach the balance, then formed a special thin layer formation potential difference, forming a p-n junction.After the chip by light, p-n junction, the N type semiconductor hole move P type area, and electrons move N area of P type area, thus forming the current from the n-type area to the P type.And then began to form in PN junction potential difference, this creates a power supply.Here is such a power supply.

Due to the semiconductor are not good conductors of electricity, electronics if after through the p-n junction flow in the semiconductor, resistance is very large, the loss is very large.But if in the upper all painted metal, the sun can't through, current will not be able to produce, so generally cover p-n junction with metal grid (as shown in figure comb electrode), in order to increase the area of the incident light.

Another silicon surface is very light, reflecting off a lot of sunlight, cannot be used battery.To do this, scientists give it coated with a layer of protective film of reflection coefficient is very small, is based on the actual industrial production using chemical vapor deposition deposited a layer of silicon nitride film, thickness of around 1000.To reduce reflection loss to 5% or less.A battery can provide current and voltage, after all, is limited, so people will be a lot of battery (typically 36) used in parallel or in series, solar photovoltaic panels.

2.Silicon solar cell production process

Is usually the crystalline silicon solar cells in 350 ~ 450 microns thick, made of high quality silicon including the silicon wafers from the lift or sawing on silicon ingot casting.

The actual consumption of silicon material more.In order to save material, the preparation of polycrystalline silicon thin-film batteries by chemical vapor deposition method, including low pressure chemical vapor deposition (LPCVD) and plasma enhanced chemical vapor deposition (PECVD) technique process.In addition, the method of liquid phase epitaxy (LPPE) and sputtering deposition could also be used to the preparation of polycrystalline silicon thin-film batteries.

Second, the nanometer crystal solar cell chemistry

In the solar cell silicon solar cell is undoubtedly the most mature development, but because the cost is high, far cannot satisfy the requirement of large-scale popularization and application.Therefore, people have been constantly in technology, new material, cell membrane and exploration on the aspects, such as, and the recent development of nanometer TiO2 crystal chemical energy solar cells have drawn the attention of the domestic and foreign scientists.

To dye sensitized nanocrystalline solar cells (DSSCs) as an example, the battery is mainly including the glass substrates coated transparent conductive film, dye sensitized semiconductor material, the electrode and electrolyte and so on several parts.

Anode: dye sensitized semiconductor film (TiO2 film)

Cathode: platinum plated conductive glass

Electrolyte: I3 / I

As shown, the white ball said TiO2, red ball said dye molecules.Dye molecules to absorb the sun light energy transition to the excited state, excited states, electronic quickly into adjacent to the TiO2 conduction band, lost electrons dye quickly get compensation from the electrolyte, into the TiO2 conduction band of electricity to end up in conductive film, and then through the outer loop generated photocurrent.

The advantages of the nanocrystalline TiO2 solar cells is its cheap cost and simple process and stable performance.Its stable photoelectric efficiency over 10%, production costs only 1/5 ~ 1/10 for silicon solar cell.Life can reach more than 20 years.But as a result of the research and development of such batteries, estimates that in the near future will gradually took to the market.

Three, dye sensitized TiO2 solar cells made by hand

1. The production of titanium dioxide film

(1) the first grinding titanium dioxide powder in a mortar with adhesive

(2) and then slowly with a glass rod in conductive coating on the glass

(3) put the tio2 membrane into the alcohol lamp sintering under 10 ~ 15 minutes, and then cooling

2. The use of natural dyes for titanium dioxide color

Fresh or frozen blackberry, come in, pomegranate seed or black tea, add a tablespoon of water and extrusion, then put the tio2 film in color, it will take about 5 minutes, until the film into a dark purple, if both sides film color uneven, can put in to soak for 5 minutes, then rinse with alcohol, and gently dry soft paper.

3. The production of positive electrode

By dye TiO2 for electronic flow of a pole (cathode).Positive electrode can be made of conductive surface of conductive glass (SnO2 film coated with conductive layer), using a simple multimeter can judge glass side can be conductive, use your fingers can also make judgments, conductive surface is rough.As shown, the other conductive surface marked with "+", then use a pencil in conductive surface evenly coated with a layer of graphite.

4. Join the electrolyte

Using iodine ion in the solution as a solar energy battery electrolyte, it is mainly used for dye reduction and regeneration., as shown in the tio2 film on the surface, add one to two drops electrolyte.

5. Battery assembly

After the color of titanium dioxide film face up on the table, one to two drops on membrane containing iodine and iodine ion electrolyte, then into the positive electrode conductive facing down on the tio2 film.Stagger, two pieces of glass slightly clamp with two clip the batteries, part of the two pieces of glass exposed to connect wires.In this way, your solar cell is made.

6. The battery of tests

Outside the sun, to test whether your solar cells can generate an electric current.

structure

Said said of the silicon atoms, negative charge around four electronic next to the silicon atoms.

When mixed with other impurities in silicon crystal, such as boron, phosphorus, etc., when mixed with boron, silicon crystal will there is a hole in the formation of it can refer to below:

Said said of the silicon atoms, negative charge around four electronic next to the silicon atoms.And yellow said adding boron atoms, only three electrons around because of boron atoms, so can produce blue hole.

When the p-type and n-type semiconductor together in two kinds of semiconductor interface area will form a thin layer of special).N the electron will spread to P, P the hole will spread to the N area, once the diffusion is formed by a N to P "inside the electric field", so as to prevent proliferation.Until after reaching balance, has formed a special thin layer formation potential difference, this is PN junction.

Because of semiconductor are not good conductors of electricity, electronics if after through the p-n junction flow in the semiconductor, so generally cover p-n junction with metal grid (as shown in figure comb electrode), in order to increase the area of the incident light.

Another silicon surface is very light, reflecting off a lot of sunlight, cannot be used batteries, the scientists give it coated with a layer of protective film of reflection coefficient is very small.

The working principle of the silicon solar cells

Solar cell is a light have response and can convert light energy into electrical devices.Can produce the material, there are many kinds of photovoltaic effect, such as: monocrystalline silicon, polycrystalline silicon, amorphous silicon, gallium arsenide, copper indium selenium, etc.Their power generation principle of basic same, now in crystalline silicon, for example to describe the light power generation process.P-type crystalline silicon after doped phosphorus available N type silicon, forming a p-n junction.

When light solar cell surface, part of photons absorbed by the silicon material;Photon energy transfer to the silicon atom, make electronic happened more moved, a free electron concentration on both sides of p-n junction formed the potential difference, when external processing circuit, under the action of the voltage, there will be a current through the external circuit to produce the output power.The essence of this process is: the process of the photon energy into electricity.

The production process

Chemical vapor deposition mainly SiH2Cl2, SiHCl3, SiCl4 or SiH4, as the reaction gas, reaction under certain protective atmosphere of the silicon atoms and deposition on the heating of the substrate, the substrate material generally choose Si, SiO2, Si3N4, etc.But the study found that in the silicon substrate is difficult to form a larger grain size, and easy to form in intergranular space.Solution to this problem is to use LPCVD first on the substrate deposit a thin layer of amorphous silicon layer, and then the amorphous silicon layer annealing, get larger grain size, and then on the layer of seed crystal deposition thickness of polycrystalline silicon thin film, as a result, recrystallization technology is undoubtedly very important one link, the main technology of solid phase crystallization method and the central melting recrystallization method.Polycrystalline silicon thin-film batteries in addition to the recrystallization process, adopted almost all other preparation technology of monocrystalline silicon solar cell, so obviously improve the conversion efficiency of solar cells.

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