Design and Fabrication Method of Hetero-structured Solar Cell Using Non-Crystalline a-Si/poly-Si

Abstract

History of commercial production of solar cells made from polysilicon material (E.sub.ff =15 -17%) and from amorphous silicon (Eff = 9 - 12%) has accumulated understanding of deficiencies and limitations of these solar cells. The present design combines following technical requirements: a) ability to harvest energy from widest part of sun spectrum; b) offer highest values of absorption coefficient for photons of the selected part of sun spectrum; c) ensure highest efficiency of conversion of incident photons into electron-hole pairs or photocarriers while ensuring lowest recombination rate; d) The simplicity of fabrication and low cost of mass production.

Claims

1. The high efficiency of the solar cell achieved by hetero-structural combination of two noncrystalline Silicon materials, namely, a-Si (amorphous) and poly-Si (polysilicon).

2. The 0.2 .Math.m thick p-type amorphous Si is the top layer of the solar cell to absorb all photons with energy E.sub.ph>1.9 eV (from sun spectra.

3. The 99.1 .Math.m thick n-type poly-Si is the base layer of hetero-structured solar cell to absorb all photons with energy 1.1 eV<E.sub.ph <1.8 eV.

4. In agreement with claim 2 the 0.2 .Math.m thick p-type amorphous Si layer is uniformly doped by 10.sup.18cm.sup.-3 donor density to suppress recombination rate of electron -hole carriers generated by sun light.

5. In agreement with claim 3 the 99.1 .Math.m thick n-type poly-Si layer is uniformly doped by donor type impurity concentration falling in the range 10.sup.13 - 10.sup.17 /cm.sup.3 to suppress recombination rate of electron -hole carriers generated by sun light.

6. In agreement with claims 1 and 3 the 99.1 .Math.m thick n-type poly-Si base layer of heterostructured solar cell is produced by liquid epitaxy or grown as ribbon from silicon melt.

7. In agreement with claims 1 and 2 the 0.2 .Math.m thick p-type amorphous Si is the top layer of the solar cell is grown on base layer by CVD epitaxy, or any of commercial fabrication methods, such as such as SSP (Standard Screen Printed), PERC (Passivated Emitter Rear Contact) or IBC (Interdigitated Back Contact) solar cells.

8. In agreement with claims 1,2,4, and 7 the 0.2 .Math.m thick p-type amorphous Si covered by antireflection coating.

9. In agreement with claims 1 and 2 the 0.2 .Math.m thick p-type amorphous Si is the top layer of the solar cell will prevent overheating of the base layer, thus keeping efficiency of the solar cell steady under intense solar radiation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The accompanied drawings have been vividly described in the description of invention. This section describes the aspects of the drawings that are relevant to the design of the proposed solar cell.

[0012] FIG. 1. is a diagrammatic representation of an embodiment of the invention in which the a-Si layer (top layer) is doped with acceptor type (p-type) impurities and the poly-Si layer at the bottom is doped with donor type (n-type) impurities.

[0013] FIG. 2. is a diagrammatic representation of another embodiment of the invention in which the a-Si layer (top layer) is doped with donor type (n-type) impurities and the poly-Si layer at the bottom is doped with acceptor type (p-type) impurities.

[0014] FIG. 3 depicts output current vs voltage characteristics that was realized for the proposed design by using finite element analysis method. It contains value of current density in mA/cm.sup.2 plotted along y-axis and the voltage occurring between the top layer and the bottom layer of the designed solar cell along the x-axis.

REFERENCES

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