Photovoltaic cell

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

The present invention has two molecular components, namely an electron donor and an electron acceptor, particularly a photoactive layer composed of a conjugate polymer component and a fullerene component, and two metal electrodes provided on both sides of the photoactive layer. Regarding photocells. [0002]

A plastic having an extended π-electron system with alternating single and double bonds is called a conjugated plastic. This conjugated plastic has an energy band comparable to that of a semiconductor in terms of electron energy, and can shift from a non-conductive state to a metallic conductive state by doping. Examples of this conjugated plastic are polyphenylene, polyvinylphenylene (PPV), polythiophene or polyaniline. However, the energy conversion efficiency of a photocell polymer cell made of conjugated polymer is typically 10.^-3~10^-2%. To improve this efficiency, a heterogeneous layer consisting of two conjugate polymer components already using a polymer component as an electron donor and another polymer component as an electron acceptor has been proposed (US Pat. No. 5,670,791). ). Fullerene as an electron acceptor, especially Buckminsterfullerene C₆₀(US Pat. No. 5,454,880) was able to adequately avoid other conventional charge carrier recombination, which resulted in a significant increase in efficiency. Good charge separation is necessary, but not sufficient, to achieve good efficiency. This is because it is necessary to additionally consider that the separated charges reach the corresponding electrodes of the photovoltaic cell. In ordinary photovoltaic cells of this type, an electrode in which holes made of indium / tin-oxide (ITO) are collected and an electrode made of aluminum in which electrons are collected are advantageous. [0003]

Therefore, an object of the present invention is to form the photovoltaic cell of the type described at the beginning so as to increase the transfer of electric charge between the photoactive layer and the electrode in the sense of increasing the short-circuit current. [0004]

The problem is that according to the present invention, an intermediate layer made of a conjugate polymer is provided between a photoactive layer and at least one of the electrodes, the polymer has a doping corresponding to an electrode potential, and a valence band and conduction with respect to electron energy. It is solved by having an energy gap of at least 1.8 eV between the bands. [0005]

The conjugated polymer in the middle layer is doped in the sense of electrode potential, which means oxidative doping in the region of the electrode where holes gather and reduced dopins in the region of the electrode where electrons gather, so the conjugated polymer is the electrode of the electrode where holes gather. Guarantees an excess of holes in the region, but guarantees an excess of electrons in the region of the electrode where electrons gather, supports conduction of holes in the region of the oxidative doping polymer, and supports conduction of electrons in the region of the reducing doping polymer. .. However, the conjugated polymer in each intermediate layer has a relatively large energy gap of at least 1.8 eV between the valence band and the conduction band with respect to the electron energy band, resulting in a considerably high activation energy for the inherent conduction. When this is an oxidation doping polymer layer, electron conduction from the photoactive layer to the electrode where holes are collected is avoided, and when this is a reduction doping intermediate layer, hole conduction from the photoactive layer to the electrode where electrons are collected is avoided. Therefore, this special intermediate layer is used to support the conduction of charge carriers from the photoactive layer to the electrodes, which collect at the adjacent electrodes, but to prevent the diffusion of charges in the opposite poles in the same direction. Achieved. As a result of this special layer, the conduction of charge to the electrodes can be significantly improved, which directly acts on the increase in short-circuit current. Depending on the use, it is possible to use a photovoltaic cell having this intermediate layer between the electrode where holes gather and the photoactive layer, between the electrode where electrons gather and the photoactive layer, or within the region of the two electrodes. It does not have to be emphasized. [0006]

A particularly advantageous situation is achieved when the intermediate layer consists of a doped polythiophene derivative, although various conjugate polymers can be correspondingly doped by oxidation or reduction to form the intermediate layer. In this case, the terms polymer are understood to be homopolymers and oligomers. [0007]

The object of the present invention is exemplified in the drawings. [0008]

FIG. 1 is a cross-sectional view of the photovoltaic cell of the present invention, and FIG. 2 is a current-voltage characteristic curve of the conventional photovoltaic cell and the photovoltaic cell of the present invention. [0009]

The photovoltaic cell according to FIG. 1 has a light-transmitting glass support 1, and an electrode layer 2 made of indium / tin-oxide (ITO) is attached on the support. The electrode layer 2 generally forms a relatively rough surface structure, and the electrode layer is covered with a smooth layer 3 composed of a conductive polymer, generally PEDOT, by corresponding doping. Unlike conventional photovoltaic cells of this type, according to the present invention, in order to obtain a corresponding excess of holes, the photoactive layer 4 does not adhere directly on the smooth layer, but on the intermediate layer 5, and the intermediate layer It consists of a conjugate polymer oxidatively doped with nitrosonium-tetrafluoroborate after attachment to smooth layer 3, preferably poly-3-alkylthiophene. [0010]

The photoactive layer 4, which adheres on the intermediate layer 5 in the form of a solution, consists of a conjugate polymer as an electron donor, preferably a polythiophene derivative and a fullerene as an electron acceptor, particularly a functional fullerene PCBM. In this case, the terms polymer are understood to be homopolymers and oligomers. The electron integrated electrode 6 is made of aluminum, which is deposited on the photoactive layer 4 without inserting another intermediate layer in the case of the example shown, which is quite possible. In this case, the conjugate polymer in the intermediate layer should be reductively doped corresponding to the negative potential of the electrode 6 where the electrons are gathered to ensure a corresponding electron excess. [0011]

The intermediate layer 5, which has an energy gap of at least 1.8 eV between the valence band and the conduction band, makes it difficult for electrons to penetrate from the photoactive layer 4 to the intermediate layer 5 due to this relatively wide energy gap. The conduction of holes between the photoactive layer 4 and the electrode 2 where the holes gather is not impaired. Unlike the PEDOT layer 3, for example, the conduction band of the conjugate polymer of the intermediate layer 5 exists at an energy level clearly higher than the energy band of the electron acceptor of the photoactive layer 4. This means a unipolar charge transfer from the photoactive layer 4 to the electrode 2 where the holes collect, which is seen in the corresponding increase in short circuit current as can be seen in FIG. In FIG. 2, the photovoltaic cell of the present invention compared to a cell having a matching structure except for the intermediate layer 5 is 80 mW / cm under simulated AM1.5 conditions.²The current density I is plotted against the voltage U with the excitation energy of. The characteristic curve 7 belonging to the photovoltaic cell of the present invention produces a short-circuit current measured at a voltage U = 0V, which is shown to be about twice as large as the short-circuit current of the comparison cell according to the characteristic curve 8. [0012]

It does not need to be explained in detail that the spacing between the valence bands is decisive and the spacing between the conduction bands is decisive in the case of the arrangement of the intermediate layer 5 between the photoactive layer 4 and the electrode 6 where the electrons gather. [0013]

Since the action of the electrically insulating transition layer 6 is not limited to the covenant polymer as an electron donor and fullerene as an electron acceptor, the action of the present invention has a two-component layer of a molecule consisting of an electron donor and an electron acceptor. It can be recognized for all photovoltaic cells.

[Simple explanation of drawings]

[Figure 1]

It is sectional drawing of the photovoltaic cell of this invention. [Figure 2]

It is a graph which shows the comparison of the current-voltage characteristic curve of the conventional photovoltaic cell and the photovoltaic cell of this invention. [Explanation of symbols]

2 electrodes, 4 photoactive layers, 5 intermediate layers, 6 electrodes