PHOTOVOLTAIC CELL STRUCTURE AND METHOD TO PRODUCE THE SAME

Abstract

The object of the present invention is a photovoltaic cell structure, comprising a p-type semiconductor substrate with a bottom electric contact, upon which a layer comprising ZnO nano structures is made, covered with a Zn Mg O layer and with a transparent conductive layer, preferably ZnO:Al layer, with an electric contact, characterized in that the active layer is a Si/ZnO/ZnMgO junction, the layer of ZnO nano structures of the height of 100 nm up to 2000 nm being covered with the ZnMgO layer from 1 nm to 2000 nm thick, and the method to produce the same.

Claims

1. A photovoltaic cell structure, containing a p-type semiconductor substrate with bottom electric contact, with a layer comprising ZnO and ZnMgO covered with a transparent conductive layer, preferably ZnO:Al layer, with an electric contact, characterized in that the active layer is a Si/ZnO/ZnMgO junction, the layer of ZnO nanostructures of the height of 100 nm up to 2000 nm being covered with the ZnMgO layer from 1 nm to 2000 nm thick.

2. The structure according to claim 1, characterized in that the nucleating layer for growing ZnO nanostructures is a layer of gold, silver or ZnO, or nanoparticles of these materials.

3. The method to produce photovoltaic cell, wherein layer containing ZnO and ZnMgO covered with a deposited transparent ZnO:Al layer with an electric contact is deposited on a p-type substrate with a bottom electric contact, characterized in that a layer of ZnO nanostructures in the form on nanorodes covered with a ZnMgO is created upon a substrate, preferably silicon one, wherein in order to create the said layer, the substrate is first covered with a nucleating layer and then the substrate with the nucleating layer is placed in a reacting mixture with pH of 6.5-12, containing a solvent, at least one oxygen precursor and at least one zinc precursor, zinc concentration being from 0.001 M/dm3 to 1 M/dm3, heated up to the temperature of 30-95 C. and maintained at that temperature for at least 1 second, and upon completion of the process, impurities are removed from the crystallized nanostructures, preferably by annealing for at least 1 second in the temperature of 100 C., after which the nanostructures are covered with a ZnMgO layer at least 1 nm thick in an ALD process, and so created active layer is covered with a transparent ZnO:Al electrode upon which the upper electric contact is made.

4. The method of claim 3, characterized in that the nucleating layer is deposited on the substrate be means of cathode sputtering of gold, silver, or nanoparticles of those metals.

5. The method of claim 3, characterized in that the nucleating layer is a ZnO layer or ZnO nanoparticles deposited on the substrate from a solution or obtained by annealing zinc salts deposited from a solution, or deposited in at least 1 ALD cycle, the precursor of zinc being diethylzinc, dimethylzinc or zinc chloride, and the precursor of oxygen being water, ozone, or oxygen plasma.

6. The method of claim 3, characterized in that the oxygen precursor in the reaction mixture is water, and the zinc precursor is zinc acetate.

7. The method of claim 3, characterize in that the ZnMgO layer that the active layer nanorodes are covered with is deposited in at least 10 ALD cycles, using diethylzinc, dimethylzinc or zinc chloride as zinc precursor, bis(methylcyclopentadienyl)magnesium as Mg precursor, and water, ozone or oxygen plasma as oxygen precursor.

8. The method of claim 3, characterized in that the transparent ZnO:Al layer is deposited in at least 100 ALD cycles, using diethylzinc, dimethylzinc or zinc chloride as zinc precursor, water, ozone or oxygen plasma as oxygen precursor, and trimethylaluminum as aluminum precursor.

Description

EXAMPLE 2

[0005] To carry out the second example structure, commercially available p-type silicon substrate with electrical resistivity of 2.3 cm and dimensions of 1.51.5 cm was also used. First, the substrate was subjected to cleaning that was carried out in a ultrasonic washer. The substrate was washed for 30 seconds, consecutively in deionized water. Aluminum film 2, constituting the bottom electric contact, was deposited with cathode sputtering upon the cleaned substrate 1. In the second step, the creation of the active ZnO layer in the form of ZnO nanorods 4 covered with thin film of ZnO 5 upon the cleaned substrate was commenced. For that purpose, nanoparticles ZnO being the nucleation layer 3 for hydrothermal growth of nanorodes were deposited upon the upper surface of the substrate 1 in 10 ALD cycles and temperature of 100 C., using water as oxygen precursor and diethylzinc as zinc precursor. Next, the substrate with the nuclei was placed in 110 ml of a reaction mixture containing 2 g dissolved zinc acetate and brought to the pH equal 7.7 by precipitation with 1-mol potassium hydroxide solution. The mixture with the substrate was heated to the temperature of 70 C. and the growth of nanorodes to the height of 1200 nm was continued in that temperature for 2 minutes. After the growth completed, the substrate 1 with the crystallized nanorods 4 was rinsed in isopropanol to remove possible impurities, and deposition of ZnO layer 5 upon them started. For that purpose, the substrate was placed in an ALD reactor where it was annealed for 2 minutes in 200 C. After annealing, the reactor chamber was cooled down to 160 C., and the ZnO nanorodes were thoroughly covered with a ZnMgO layer ca. 1000 nm thick in 4000 ALD cycles at that temperature. The ZnMgO layer 5 was deposited with diethylzinc as zinc precursor, water as oxygen precursor, and bis(methylcyclopentadienyl)magnesium as magnesium precursor. Further on, at the same temperature and without removing the substrate with the deposited ZnO nanostructures covered with ZnMgO layer from the ALD reactor, the transparent electrode layer 6 in the form of ZnO:Al and thickness of 500 nm being the upper transparent electrode 6 was deposited. The electrode layer 6 was deposited with diethylzinc as zinc precursor, water as oxygen precursor, and trimethylaluminum as aluminum precursor. Having deposited electrode layer 6, the point ohmic contact with the ZnO:Al layer 7, made of aluminum, was deposited by cathode sputtering process. The obtained structure demonstrated the efficiency of 5% (laboratory measurements made with sunlight simulator). On application of higher ZnO nanorodes or even thicker ZnMgO layer, the cell efficiency decreases dramatically. For nanorodes higher than 2000 nm and ZnMgO layer thicker than 2000 nm, the cell efficiency is close to 0the cell stops working.