1 / 31

Cell and module construction

Cell and module construction. Photovoltaic effect and basic solar cell parameters. To obtain a potential difference that may be used as a source of electrical energy, an inhomogeneous structure with internal electric field is necessary. Suitable structures may be: PN junction

hali
Download Presentation

Cell and module construction

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Cell and module construction

  2. Photovoltaic effect and basic solar cell parameters • To obtain a potential difference that may be used as a source of electrical energy, • an inhomogeneous structure with internal electric field is necessary. • Suitable structures may be: • PN junction • heterojunction (contact of different materials).

  3. Important solar cell electrical parameters • open circuit voltage VOC, • short circuit current ISC • maximum output power VmpImp • fill factor • efficiency Vmp VOC • Parameters VOC, ISC, FF and η are usually given for standard conditions: • spectrum AM 1.5 • radiation power 1000 W/m2 • cell temperature 25°C.

  4. Modelling I-V characteristics of a solar cell PN junction I-V characteristics Parallel resistance Rp Series resistance RS Aill – illuminated cell area A - total cell area Output cell voltage V = Vj- RsI

  5. To maximise current density JPV • it is necessary • maximise generation rate G • minimise losses losses electrical optical recombination • reflection • shadowing • not absorbed radiation • emitter region • base region • surface • series resistance • parallel resistance

  6. Series resistance Rs influences strongly solar cells efficiency Series resistance Rs consists of: ·R1 – contact metal-semiconductor on the back surface ·R2 – base semiconductor material ·R3 – lateral emitter resistance between two contact grid fingers · R4 – contact metal-semiconductor on the grid fingers ·R5 – resistance of the grid finger ·R6 – resistance of the collector bus

  7. R3 – lateral emitter resistance between two contact grid fingers Decrease of ρN is connected with increasing ND Auger recombination rate increases Decrease of the finger distance d results in a decrease of illuminated area Aill It is very important to optimise xj

  8. Optimising PN junction depth The photo-current density JPV consists from carriers collected by the electric field in the space charge region of the PN junction, i.e. from carriers generated in a distance of about diffusion length from the PN junction. The PN junction depth xj should be less than 0.5 μm (0.2 m is desirable).

  9. Construction of solar cells • To obtain high efficient solar cell it is necessary • maximise IPV and Rp • minimise Rs In the illuminated area generated excess carriers diffuse towards the PN junction. The density JFV is created by carriers collected by the junction space charge region • in the N-type region • in the P-type region • in the PN junction space charge region

  10. More detail information can be obtain from solution of continuity equations. Jp - current density generated in N-type layer Jn - current density generated in P-type base JOPN- generated in the PN junction space charge layer

  11. Results of simulations for different wavelength of incident light Losses due to recombination may considerably limit the cell parameters, especially, losses connected with the recombination in the P-type region.

  12. To maximise current density JPV it is necessary • maximise generation rate G • minimise recombination rate Φ0 = Φin (1 – R) R is the surface reflexivity To maximise generation rate it is necessary to minimise surface reflection, especially in the visible region of solar spectrum

  13. Antireflection coating For a monochromatic light, the minimum reflexivity Rmin occurs when the optical path is equal to a quarter of wavelength, i.e. the layer thickness is . From that follows for Silicon refraction index Thin film material of n2 2 is desirable for silicon solar cells (Si3N4 or TiO2 layers of d  75 nmare usually used for antireflection coating).

  14. 1960 -1980 • plane surface • SiO2 (TiO2) antireflection • layer • photolithography • vacuum contact deposition Theoretical efficiency limit – 18%

  15. Surface texturing If the surface has a pyramidal structure it is possible to decrease reflection on about one third of that on a plane surface. Both principles (surface texturing and antireflection coating) can be combined to minimise losses by surface reflection texturised

  16. New construction principles PEARL structure (1994) • antireflection coating • improvement • high contact quality • high quality starting (FZ) Si • minimising the structure • thickness microelectronics technology with several photolithographic processes principles of construction and technology were simplified for mass production

  17. Present construction used in mass production • Surface texturing without photolithography • etching monocrystalline (1,0,0) Si • in KOH - acid etching in the case of other crystallographic orientation of Si

  18. A single solar cell……~0.5 V, about 30 mA/cm2 For practical use it is necessary connect cells in series to obtain a source of higher voltage and in parallel to obtain a higher current Solar cell PV module PV field

  19. Cell connection in parallel Optimum situation: all cells have the same VMP If characteristics of individual cells in parallel differ, efficiency decreases

  20. Cells in series….. the same current flows through all cells voltage does sums I n cells n + 1 cells Optimum situation: all cells have the same IMP If characteristics of individual cells in series differ, efficiency decreases V

  21. Effect of partial shading – one cell(a decrease of illuminated area Aill) • In the case of one cell • a decrease of the output current (proportional to area illuminated) • a decrease of the output voltage • a decrease of the output power

  22. Effect of partial shading – cells in series • In the case of cells in series increases series resistance • a decrease of the output current • a decrease of the output voltage • a considerable decrease of the output power One cell shaded

  23. A practical example of the shading effect – a bottom of the field 2 is shaded in January by the field 1

  24. Suitable materials CuInSe2 amorphous silicon amorphous SiGe CdTe/CdS Basic types of solar cells: Crystalline silicon cells Thin film cells Basic problem: cost…...

  25. CIS Cadmium Telluride(Copper Indium Selenide) NiAl 0.5 - 1 m 0.1 m 0.03 - 0.05 m Glass MgF2 1.5 - 2.0 m 0.5 - 1.5 m ITO/ZnO CdS 0.03 -0.2 m Cu(InGa)Se2 0.5 - 1.5 m TCO CdS CdTe Molybdenum Glass Contact

  26. A simple structure of a thin film solar cell from amorphous silicon transparent substrate transparentconducting electrode a-Si:H p+layer (20 - 30 nm) a-Si:H (non-doped layer – 250 nm) a-Si:H n+layer (20 nm) Transparent conducting electrode (diffusion barrier) Silver or aluminium back reflector

  27. Light trapping

  28. Tandem cells Wg1> Wg2 irradiation

  29. “Micromorf” cells

  30. AIIIBV triple cells The highest efficiency from all solar cell types  30%

  31. High efficiency solar cell application Concentrator modules

More Related