Solar cell

A solar cell includes a back metal-contact layer, a P-type semiconductor layer, a P-N junction layer, an N-type semiconductor layer and a transparent electrically conductive layer. The P-type semiconductor layer is formed on the back metal-contact layer. The P-type semiconductor layer is comprised of nano particles of a P-type semi-conductive compound. The P-N junction layer is formed on the P-type semiconductor layer. The N-type semiconductor layer is formed on the P-N junction layer. The N-type semiconductor layer is comprised of nano particles of an N-type semi-conductive compound. The transparent electrically conductive layer is formed on the N-type semiconductor layer and functions as a front contact layer.

BACKGROUND

1. Technical Field

The present invention relates to solar cells, and particularly, to a solar cell made of semi-conductive compounds.

2. Description of Related Art

Currently, various solar cells have been designed to receive and convert sunlight into electrical energy. Such solar cells have been applied on roofs of buildings and cars, or applied on portable electronic devices.

In a typical solar cell, a P-type semiconductor layer and an N-type semiconductor layer are two key components. When sunlight projects on surfaces of the P-type semiconductor layer or the N-type semiconductor layer, a part of the sunlight is unavoidably reflected by the surfaces, and the other is absorbed. Photons in the absorbed sunlight collide with electrons in the P-type semiconductor layer or the N-type semiconductor layer, thereby, electron-hole pairs are generated, and thus an electric field is formed between the P-type semiconductor layer and the N-type semiconductor layer, i.e., a photon-electron conversion is realized.

The P-type semiconductor layer and N-type semiconductor layer of the solar cell can be made of silicon based materials, or semi-conductive compounds. However, cost of the silicon based materials is hard to be reduced. In addition, lattice defects, such as dislocations and stacking faults, are prone to occur in the semiconductor layers during formation when the semi-conductive compounds are used, and thus the efficiency of the photon-electron conversion is difficult to be improved.

What is needed, therefore, is a solar cell with fewer lattice defects and higher photon-electron conversion efficiency using the semi-conductive compounds.

SUMMARY

An exemplary solar cell includes a back metal-contact layer, a P-type semiconductor layer, a P-N junction layer, an N-type semiconductor layer and a transparent electrically conductive layer. The P-type semiconductor layer is formed on the back metal-contact layer. The P-type semiconductor layer is comprised of nano particles of a P-type semi-conductive compound. The P-N junction layer is formed on the P-type semiconductor layer. The N-type semiconductor layer is formed on the P-N junction layer. The N-type semiconductor layer is comprised of nano particles of an N-type semi-conductive compound. The transparent electrically conductive layer is formed on the N-type semiconductor layer and functions as a front contact layer.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present solar cell will now be described in detail below and with reference to the drawing.

Referring to the drawing, an exemplary solar cell100is shown. The solar cell100includes a substrate10, a back metal-contact layer20, a P-type semiconductor layer30, a P-N junction layer40, an N-type semiconductor layer50and a transparent electrically conductive layer60.

The substrate10can be rigid or flexible according to need. A material of the substrate10can be selected from glass, ceramic, plastic and stainless steel.

The back metal-contact layer20is comprised of a material selected from silver, copper, molybdenum, aluminum, copper aluminum alloy, silver copper alloy, and copper molybdenum alloy. The back metal-contact layer20is formed on the substrate10by DC magnetron sputtering.

The P-type semiconductor layer30is comprised of nano particles of a P-type semi-conductive compound. The P-type semi-conductive compound can be selected from a group consisting of nano aluminum gallium arsenide (AlGaAs), nano aluminum gallium nitride doped with hydrogen (AlGaN:H), and nano aluminum gallium nitride doped with magnesium (AlGaN:Mg). The P-type semiconductor layer30is deposited on the back metal-contact layer20by plasma-enhanced chemical vapor deposition (PECVD) or metal-organic chemical vapor deposition (MOCVD). A thickness of the P-type semiconductor layer30is in the range from 1 μm to 10 μm. In order to lower roughness Ra, a size of each particle in the P-type semi-conductive compound is beneficially in the range from 10 nm to 100 nm. Due to the nano size of the P-type semi-conductive compound, it is much easier for the P-type semiconductor layer30to have a same lattice distribution as the back metal-contact layer20, thereby, lattice defects, such as dislocations and stacking faults can be reduced. The P-type semiconductor layer30can also have a smooth surface with minimum surface roughness.

The P-N junction layer40is comprised of copper indium gallium diselenide (CuIn1-xGaSe2). The P-N junction layer40is formed on the P-type semiconductor layer30, and configured for joining the P-type semiconductor layer30and the N-type semiconductor layer50. Due to the smooth surface of the P-type semiconductor layer30, contact between the P-N junction layer40and the P-type semiconductor layer30is enhanced, and thus reducing barrier and friction for the electrons or holes movements therebetween.

The N-type semiconductor layer50is comprised of nano particles of an N-type semi-conductive compound. The N-type semi-conductive compound can be selected from a group consisting of nano gallium nitride, nano gallium nitride doped with silicon, and nano indium gallium phosphide. The N-type semiconductor layer50is deposited on the P-N junction layer40by plasma-enhanced chemical vapor deposition (PECVD) or metal-organic chemical vapor deposition (MOCVD). A thickness of the N-type semiconductor layer50is in the range from 0.5 μm to 10 μm. In order to lower roughness Ra, a size of each particle in the N-type semi-conductive compound is beneficially in the range from 10 nm to 100 nm. Similar to the P-type semiconductor layer30, it is much easier for the N-type semiconductor layer50to have a same lattice distribution as the P-N junction layer40, thereby, lattice defects, such as dislocations and stacking faults can be reduced.

The P-type semiconductor layer30, the P-N junction layer40and the N-type semiconductor layer50constitute a semiconductor unit for photon-electron conversion. Lattice defects are reduced in the semiconductor unit, as a result, lattice vibration in the semiconductor unit is decreased. In this way, it is much easier for movements of the photons, electrons or holes in the semiconductor unit, and high photon-electron conversion efficiency can be obtained.

The transparent electrically conductive layer60is formed on the N-type semiconductor layer50. The transparent electrically conductive layer60functions as a front contact layer. The transparent electrically conductive layer60can be a transparent electrically conductive oxide film, for example, indium tin oxide (ITO) or zinc oxide, and a thickness of the transparent electrically conductive layer60may be in the range between 300 nm to 900 nm. Alternatively, the transparent electrically conductive layer60can be a carbon nanotube film, and a thickness of the transparent electrically conductive layer60may be in the range between 30 nm to 300 nm. The carbon nanotube film is comprised of a number of carbon nanotubes, and the carbon nanotubes are preferably oriented in parallel with the N-type semiconductor layer50.

In use, the solar cell100can be applied on, for example, a roof of a building for the photon-electron conversion.

It is understood that the above-described embodiments are intended to illustrate rather than limit the invention. Variations may be made to the embodiments and methods without departing from the spirit of the invention. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.