JPS6233757B2 - - Google Patents

Description

[Detailed description of the invention] This invention relates to solar cells.

In conventional solar cells, amorphous materials such as hydrogenated amorphous silicon or polycrystalline silicon materials are used as materials for photoconductive thin films.
We are trying to reduce costs and increase the area.

However, in general, these materials have small carrier mobility and lifetime, and therefore the diffusion length is extremely short compared to crystals, often less than the light absorption length of thin films, and the junction electric field The drift range is also often less than the optical absorption length. Therefore, it has the disadvantage that sufficient energy conversion efficiency cannot be obtained.

Therefore, an object of the present invention is to provide a solar cell with high energy conversion efficiency.

A first embodiment of the invention is shown in FIGS. 1A and B.
A detailed description will be given below with reference to the cross-sectional views shown in and the energy band diagrams corresponding thereto.

That is, this solar cell includes a photoconductive thin film 1 made of a semiconductor or an insulator, a mesh-like first output electrode 2 and a first insulating film each having a light-transmitting property and which are bonded to one surface of the photoconductive thin film 1 in sequence. A film 3 and a first pulse applying electrode 4, and the photoconductive thin film 1
A mesh-like second output electrode 2', a second insulating film 3', and a second pulse application electrode 4' are successively bonded to the other surface, and the first pulse application electrode 4 and the first pulse application electrode 4' are connected to each other.
By applying a positive pulse voltage P 1 and a negative pulse voltage P ₂ from the outside between the output electrodes 2 and between the second pulse applying electrode 4' and the second output electrode ₂ ', the photoconductive thin film 1 is Each is correct within,
Photoconductive thin film 1 is formed by inducing negative polarization charges 6, 5.
An electric field is set inside the optical excitation carriers 7 and 8 to thereby obtain an accelerating electric field for the optically excited carriers 7 and 8, thereby increasing energy conversion efficiency.

The operation will be explained below with reference to the energy band diagram shown in FIG. 1B.

between the first input terminal 9 connected to the first pulse application electrode 4 and the first output terminal 10 connected to the first output electrode 2, and between the second input terminal 9' connected to the second pulse application electrode 4'; By applying positive and negative pulse voltages P ₁ and P ₂ respectively between the second output terminal 10' connected to the second output electrode 2', a positive charge is generated in the first insulating film 3, and a positive charge is generated in the second insulating film 3. 3', negative charges are accumulated respectively, and these accumulated charges induce negative and positive polarized charges 6, 5 in the photoconductive thin film 1, and energy is generated in the center of the photoconductive thin film 1. A slope is given to the conduction band edge 11 and the valence band edge 12 of the band diagram.

Photoexcited electrons are excited in the photoconductive thin film 1 by the incident light 13 from the side to which the first pulse applying electrode 4, the first insulating film 3, and the first output electrode 2, each of which has a light-transmitting property, are attached. 7 and photoexcited hole 8, respectively 14 and 1 in the energy band diagram of FIG.
5, and each accumulated charge is
When the potentials of V ₁ and V ₂ are reached, the first output electrode 2
It is then taken out from the first output terminal 10 and second output terminal 10' connected to each of these output electrodes 2, 2' via the second output electrode 2'.

In the above operation, if the mobility of the optically excited carriers 7 and 8 is μ and the lifetime is τ, the relationship L _d =Eμτ holds between the drift range L _d of the optically excited carriers 7 and 8. By increasing the internal electric field E, the drift range L _d can be set to be greater than the light absorption length of the photoconductive thin film 1, and the energy conversion efficiency can be improved.

A second embodiment of the invention is shown in FIGS. 2A and B.
A detailed description will be given below with reference to the cross-sectional views shown in and the energy band diagrams corresponding thereto.

That is, in this solar cell, the layer structure of the photoconductive thin film 1' in the first embodiment is modified such that an I-type semiconductor layer 1'c is sandwiched between a P-type semiconductor layer 1'a and an N-type semiconductor layer 1'b. A P-type semiconductor layer 1'a is arranged on the first output electrode 2 side, and an N-type semiconductor layer 1'b is arranged on the second output electrode 2' side.

Because of this configuration, in the first embodiment, instead of the polarized charges 5 and 6 being induced in the photoconductive thin film 1 by applying the positive and negative pulse voltages P ₁ and P ₂ , , in this embodiment, the P-type semiconductor layer 1'
Negative ion space charge due to acceptor in a 14,N
A positive ion space charge 15 is generated by the donor in the type semiconductor layer 1'b, and as shown in the energy band diagram shown in FIG. 2B, almost the same operation as in the first embodiment is performed, and the same It is possible to improve energy conversion efficiency.

A third embodiment of the invention is shown in FIGS. 3A and 3B.
A detailed description will be given below with reference to the cross-sectional views shown in and the corresponding energy band diagrams.

That is, in this solar cell, the layer structure of the photoconductive thin film 1'' in the first example is changed to the layer structure of the photoconductive thin film 1'' in the first example.
The IN structure has an I-type semiconductor layer 1''a on one side where the output electrode 2 is attached, and an N-type semiconductor layer 1''b on the other side where the second output electrode 2' is attached, and 1 output electrode 2 and the I-type semiconductor layer 1''
The connection with a is a shot connection,
The rest of the structure is the same as that of the first embodiment.

Therefore, in its operation, instead of the polarized charges 5 and 6 being induced in the photoconductive thin film 1 by the application of positive and negative pulse voltages P ₁ and P ₂ in the first embodiment, In this embodiment, a positive ion space charge 16 is generated by the donor in the N-type semiconductor layer 1''b, and the energy band diagram shown in FIG. 3B is almost the same as that in the first embodiment. The operation is performed and the energy conversion efficiency can be improved as well.

I-type semiconductor layer 1″a in the third embodiment
A specific example employing a weak N-type layer of hydrogenated amorphous silicon will be described in detail below.

In hydrogenated amorphous silicon thin films, the mobility of holes is small, so the output is regulated by the hole current value, and the hole lifetime is τ and the film thickness is L.
It is necessary to satisfy the relationship L≦Eμτ, and in this example, μ=10 ⁻³ to 10 ⁻² cm ² /V·sec τ=10 ⁻⁶ sec L=Iμm.

Therefore, it is sufficient to apply an electric field corresponding to E=10 ⁴ to ^{10 5} V/cm.

This electric field is applied between _the first input terminal 9 and the first output terminal 10 and between _the second input terminal 9' and the second This can be obtained by applying a pulse voltage with an amplitude of about 10 V between the output terminals 10'.

Film formation in other areas and selection of materials other than Si ₃ N ₄ are the same as in conventional solar cells using hydrogenated amorphous silicon.

In this example, a weak N-type layer of hydrogenated amorphous silicon is used as the I-type semiconductor layer 1''a, but the present invention is not limited thereto, and a weak P-type layer may also be used.

It was confirmed that the energy conversion efficiency of the thus obtained solar cell with respect to the sunlight irradiation intensity AMI was several times that of a normal hydrogenated amorphous silicon solar cell, resulting in high energy conversion efficiency.

As described above, the solar cell of the present invention includes a photoconductive thin film, a first output electrode that is sequentially bonded to one surface of the photoconductive thin film, and has a light-transmitting property, and a first output electrode that has translucency.
an insulating film, a first input electrode, and a second output electrode, a second insulating film, and a second input electrode sequentially bonded to the other surface of the photoconductive thin film, and between the first input electrode and the first output electrode. and the second input electrode and the second input electrode.
Pulse voltages of opposite polarity are applied between the output electrodes to accumulate charges of opposite polarity in the first insulating film and the second insulating film, and the accumulated charges cause photoexcitation in the photoconductive thin film. Since an accelerating electric field is generated for the carrier and an electromotive force is obtained between the first output electrode and the second output electrode, charges are accumulated in the insulating film by applying a pulse voltage from the outside. This accumulated charge provides an accelerating electric field for photoexcited carriers within the photoconductive thin film, thereby providing the effect of significantly improving energy conversion efficiency.

[Brief explanation of the drawing]

FIGS. 1A and B are sectional views and energy band diagrams corresponding to the first embodiment of the present invention, and FIGS. 2A and B are sectional views of the second embodiment of the invention, respectively. and the corresponding energy band diagrams, FIGS. 3A and 3B, are the third embodiment of this invention.
2 is a cross-sectional view showing an example of the present invention and an energy band diagram corresponding to the cross-sectional view. 1, 1', 1''...Photoconductive thin film, 1'a...P type semiconductor layer, 1'b...N type semiconductor layer, 1'c...I type semiconductor layer, 1''a...I type semiconductor layer, 1 "b... N-type semiconductor layer, 2... First output electrode, 2'... Second output electrode, 3
...first insulating film, 3'...second insulating film, 4...first pulse application electrode (first input electrode), 4'...second pulse application electrode (second input electrode), 5, 6...polarization electrode,
7, 8... Optical excitation carrier, 9... First input terminal,
9'...Second input terminal, 10...First output terminal, 1
0'...Second output terminal, 11, 11', 11''...Conduction band edge, 12, 12', 12''...Valence band edge, _P1 , _P2 ...Pulse voltage.

Claims (1)

[Scope of Claims] 1. A photoconductive thin film, a first output electrode, a first insulating film, and a first input electrode that are sequentially bonded to one surface of the photoconductive thin film and each have a translucent property; a second output electrode, a second insulating film, and a second input electrode sequentially bonded to the other surface of the thin film;
Pulse voltages of opposite polarity are applied between the input electrode and the first output electrode and between the second input electrode and the second output electrode, respectively, to create a voltage of opposite polarity in the first insulating film and the second insulating film. A solar cell which accumulates electric charges, generates an accelerating electric field for a photoexcited carrier in the photoconductive thin film by the accumulated electric charges, and obtains an electromotive force between the first output electrode and the second output electrode. 2. The solar cell according to claim 1, wherein the photoconductive thin film has a PIN structure in which the bonding surface side of the first output electrode is a P-type semiconductor layer. 3. The photoconductive thin film has an IN structure in which the bonding surface side of the first output electrode is an I-type semiconductor layer, and the first output electrode and the I-type semiconductor layer form a shot junction. A solar cell according to claim 1.