JPH0716021B2 - Photovoltaic device and manufacturing method thereof - Google Patents

Description

TECHNICAL FIELD The present invention relates to a large-area and inexpensive photovoltaic device and a method for manufacturing the same.

2. Description of the Related Art As a photoconductive layer in a photovoltaic device, there are Si crystal, amorphous silicon, or II-VI group compound semiconductor. In the former photovoltaic device using a silicon-based material, it is difficult to provide a large-area photovoltaic device at low cost, and in the latter photovoltaic device using a II-VI group compound semiconductor, There are concerns about various problems such as pollution.

Recently, as a means for solving the above problems, a photovoltaic device using an organic semiconductor material has been developed. These are Schottky junction type in which magnesium phthalocyanine (denoted as MgPc) capable of forming a film by vapor deposition etc. is sandwiched between dissimilar metal electrodes aluminum (Al) and silver (Ag), or p-n control is performed for polyacetylene to perform pn junction. It has been reported that a type photovoltaic element is formed.

In terms of materials, it has a Schottky junction type structure, and it has excellent thermal stability and is expected to have long-term stability.
-Phenylene) sulfide (hereinafter referred to as PPS) is formed by vacuum vapor deposition to a thickness of 0.05 to 0.15 μm, and the electrode is Al.
Photovoltaic devices composed of copper and copper (Cu) have been reported. (Journal of the Chemical Society of Japan, 1983, (6), p763 ~ 768) PPS is an engineering plastic with excellent heat resistance and processability, so it is non-polluting and inexpensive. Highly expected.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention In a photovoltaic device using a PPS film formed by directly vacuum-depositing a PPS polymer having a large molecular weight, the dark specific resistance of the PPS film is large, and the metal-insulator-metal (M
IM) is similar to the structure. Therefore, there is a problem that sufficient short-circuit current cannot be obtained.

A further problem is that the engineering band gap of PPS is large, and the highest photoelectric conversion efficiency is in the near-ultraviolet region of ~ 300 nm. Therefore, the practical photoelectric conversion efficiency is disadvantageous as compared with the conventional photovoltaic device.

Means for Solving the Problems In a photovoltaic device using a photoconductive layer that generates carriers by photoexcitation, at least a part of the photoconductive layer contains a linear polymer layer containing p-phenylene as a main component. there in the infrared absorption spectrum of the linear polymer layer, the intensity of the absorption spectra for CH out-of-plane deformation vibration of a benzene ring having para-disubstituted group in the vicinity 825Cm ^-1, near 750 cm ^-1 C of benzene ring with monosubstituent
The ratio of the out-of-plane bending vibration to the intensity of the absorption spectrum is
0.9 or more and 2.5 or less.

Action The photoconductive layer required for a photovoltaic device is required to have high carrier generation efficiency and high carrier lifetime and mobility.

The movement of carriers in the bulk of a polymer is a result of intramolecular chain conduction and intermolecular chain conduction, and mobility is improved from both sides. The first guideline for the improvement of intramolecular chain conduction is the expansion of molecular orbitals and the development of a conjugated system accompanying it, and charged solitons, bipolarons, polarons, etc. are considered as conduction mechanisms. Therefore, in order to develop a conjugated system, it is necessary to have many π electrons in the main chain skeleton. It is also an effective means to bring a positive charge onto the main chain by exchanging charges with the electron acceptor. Further, it may have a structure in which electron orbits capable of hopping are adjacent to each other even if conjugation along the main chain is not developed.

The improvement of the second interchain conduction is classified into the improvement of crystallinity and the orientation. In any case, to facilitate transfer of the carrier to the adjacent polymer, the molecular chains are spatially densely arranged,
Moreover, it is necessary that the overlap of the electron trajectories in which the carriers move is large.

The length of the molecular chain has a large effect on crystallinity and orientation,
This results in a decrease in crystallinity due to a longer molecular chain, a decrease in carrier hopping probability, and an increase in carrier capture probability. The molecular chain length has a length suitable for the most densely arranged molecules as a bulk. By aligning the molecules to this length, the second interchain conduction can be improved.

The present invention is based on the finding that a polymer having a small number of phenylene groups along the main chain of a linear polymer having a molecular chain length of 4 or more and 15 or less has high conductivity and photoconductivity. is there.

That is, this condition can be satisfied by the above configuration, and good characteristics are realized.

Example FIG. 1 is a schematic cross-sectional view of an example of a basic photovoltaic device according to the present invention.

The photovoltaic device shown in FIG. 1 includes a photoconductive layer 3 including a first electrode 2 and a polymer layer on a support 1 as a photovoltaic device.
And a second electrode 4 on the photoconductive layer 3.

At least a part of the photoconductive layer 3 is mainly composed of a linear polymer layer containing p-phenylene. The linear polymer layer has an infrared absorption spectrum of 825 cm ^-1.
Of the absorption spectrum for the CH out-of-plane bending vibration of a benzene ring having a para-disubstituted group in the vicinity of the absorption spectrum of the CH-out-of-plane bending vibration of a benzene ring having a single substituent in the vicinity of 750 cm ^-1 The ratio to the strength is 0.9 or more and 2.5 or less.

In addition, since these polymers have p-type semiconductor characteristics, even higher photoelectric conversion efficiency can be obtained by heterojunction of other n-type semiconductor materials such as inorganic semiconductors such as amorphous silicon containing CdS and group III elements. Can be realized.

Further, even in an organic material, high photoelectric conversion efficiency can be realized by a heterojunction with another organic semiconductor such as a phthalocyanine pigment having a large ionization potential.

Furthermore, by forming a substituent at a position other than the para-position of p-phenylene, or by forming an atom with a large mass such as Se or Te, the action on the main chain skeleton can be increased to allow light to reach the visible light region. A device with electromotive force is obtained.

The linear polymer layer can be easily formed by a vapor deposition method using an oligomer having a phenylene group number of 4 or more and 15 or less along with the main chain of the linear polymer as an evaporation source, and has excellent characteristics. Is obtained.

Further, by performing the heat treatment at a temperature lower than the melting point temperature of the polymer, the regularity of the arrangement of the molecular chains is further improved, and a more excellent photovoltaic device can be obtained.

In the present invention, the organic semiconductor forming a heterojunction with the polymer layer in the photoconductive layer includes (1) phthalocyanine pigment (referred to as Pc), for example, XPc (X = H ₂ , Si (OH) ₂ ,
Etc.), AlClPcCl, TiOClPcCl, InClPcCl, InClPc, InBrP
cBr and the like, (2) monoazo dyes, disazo dyes and other azo dyes, (3) perenic anhydride and penylene acid imide and other penylene pigments, (4) indigoid dyes,
(5) Polycyclic quinones such as quinacridones, (7) Cyanine dyes, (8) Xanthene dyes, (9) Charge transfer complexes such as PVCz / TNF, (10) Pyrylium salt dyes and polycarbonate resins A thin film having a thickness of 0.02 to 0.1 μm can be formed by vapor deposition of a crystalline complex, (11) azurenium salt compound, or the like.

In the present invention, a vacuum deposition method, an ion class beam method, or the like is used for forming these organic semiconductors or polymer layers.

Further, in the present invention, the following amorphous layer containing silicon can be used as an inorganic semiconductor forming a heterojunction with the polymer layer used for the photoconductive layer. As the amorphous layer, a-Si (: H: X), a-Si _{1-y Cy} (: H: X) (0 <
y <1), a-Si _1-y O _y (: H: X) (0 <y <1), a-Si _1-y
N _y (: H: X) (0 <y <1), a-Si _1-z Ge _z (: H: X) (0 <
z <1), a- (Si _1-z Ge _z ) _1-y N _y (: H: X) (0 <y, z <
1), a- (Si _1-z Ge _z ) _1-y O _y (: H: X) (0 <y, z <
1), or a- (Si _1-z Ge _z ) _1-y C _y (: H: X) (0 <y, z
A single layer of <1) or a layer formed by stacking these layers can be used. It can also be used when y is continuously changed.

At this time, the film thickness of the photoconductive layer may be 0.02 to 1.0 μm, preferably 0.1 to 0.5 μm.

Further, a vapor deposition film of a II-VI group compound semiconductor such as CdS may be used as another inorganic semiconductor.

When using a non-single-crystal layer containing a chalcogen atom, a combination of the following is preferable. Ge-S, Ge
-Se, Ge-Te, Ge-P-S, Ge-P-Se, Ge-P-Te,
Ge-As-S, Ge-As-Se, Ge-As-Te, Ge-Sb-S, Ge
-Sb-Se, Ge-Sb-Te, Ge-As-Te-Se, Ge-As-S-
Te, K-Ca-Ge-S, Ge-Te-Sb-S, etc., or chalcogenide glass containing Si instead of Ge,
Ge-Si-As-Se and Ge-Si-As-Te chalcogenide glasses are mentioned.

When an amorphous layer containing silicon is formed and used as the photoconductive layer, SiH ₄ , Si ₂ H ₆ , Si ₃ H ₈ , SiF ₄ , and SiCl _{4 are used} .
_{4, SiHF 3, SiH 2 F} 2, SiH 3 F, SiHCl 3, SiH 2 Cl 2, SiH 3 plasma CVD method using a source gas of Si atoms, such as Cl, or a polycrystalline silicon as a target, Ar and H ₂ (more F ₂ or
Cl ₂ may be mixed) may be used for reactive sputtering in a mixed gas.

Further, in the present invention, in order to obtain desired characteristics, n
As an n-type impurity imparting type conductivity, N, P, As, Sb or the like belonging to Group Vb of the periodic table may be added and used.

Examples will be described below.

Example 1 On a mirror-polished glass substrate, a substrate in which platinum was formed as a first electrode to a film thickness of 0.1 μm by a sputtering method was placed in a substrate holder of a vacuum evaporation apparatus, and the residual pressure was set to 10 ⁻⁵ Pa or less. Exhausted. After that, as a photoconductive layer, PP having a phenylene group and a linear polymer having sulfur in the para position is used.
S was deposited on the substrate by vacuum deposition.

Here, the raw material powder used for vapor deposition was prepared by changing the polymerization length as follows. The polymerization method is Hawkins.
s) method (Macromolecules)
9 (1976) p. 189), crystallization melting point 150-28
Several types were prepared up to a maximum degree of polymerization of 50 at 0 ° C. At this time, the infrared absorption spectrum of each sample was 825 cm ^-1.
The absorption spectrum intensity of the benzene ring having a para-disubstituted group in the vicinity for CH out-of-plane bending vibration is about 750 cm ^-1. Ratio to (hereinafter referred to as m _* )
Was 0.7 to 7.5. Here, when m _* = 0.9, the average polymerization length is about 4.

The average degree of polymerization as raw material powder is 3.5, 4.0, 5.0, 8.0, 10,
A film thickness of 0.1 μm was formed by a vacuum deposition method using six kinds of oligomers 15 and 20. The film forming conditions at this time are the same, the degree of vacuum is 10 ^-5 Torr or less, the substrate temperature is room temperature, and the deposition source temperature is 250.
It was set to ~ 350 ° C.

After formation, the films have m _* = 0.8, 0.9, 1.3, 1.6, 2.
It became 5, 3.0 and 3.5. Therefore, the average degree of polymerization of the raw material powder is preferably 4-10.

Each of these films was subjected to heat treatment at a temperature near the melting point, which is lower than the melting point. The temperature at this time is preferably within the melting point -15 ° C. Because, at a temperature below this, it takes 5 hours or more to significantly improve the crystallinity by heat treatment, and in the vicinity of the melting point, the crystallinity may decrease.

Taking m _* = 1.6 as an example, Al is used as the second electrode on this film.
When a photovoltaic device is formed by thinly depositing as a transparent electrode, the characteristics of this device are 10 μw / c using ultraviolet light of 325 nm.
When light irradiation of m ² was performed, the open-circuit voltage was 0.5 V, the short-circuit current was 2.3 × 10 ^-8 A / cm ^2, and the short-circuit current was greatly improved. The fill factor (hereinafter referred to as FF) was 0.31 and converted. The efficiency was 2.0% if the transmittance of the electrode was corrected.

Regarding a series of photovoltaic devices having such an element structure,
Table 1 summarizes the conversion efficiencies after the evaluation was performed using ultraviolet light of 325 nm and 10 μw / cm ² and the transmittance of the electrodes was corrected.

The conversion efficiency improves as m _* increases from 0.9,
Above 2.5, it drops sharply.

On the other hand, a commercially available polymer PPS powder having a molecular weight of 10,000 or more was used as an evaporation source to form a film of 0.1 μm in the same manner, and an element was obtained in the same manner as above. Similarly, the characteristics of this device were that irradiation with 10 μW / cm ² was performed using ultraviolet light of 325 nm, but the open end voltage was 0.5.
V, short-circuit current 1.3 × 10 ^-9 A / cm ² , FF 0.26, conversion efficiency of about 0.2% is not sufficient even if the electrode transmittance is taken into consideration.

On the other hand, in order to clarify the effect of heat treatment near this melting point, each wavelength (50 μW / 50 μW /
The photocurrent in cm ² ) was measured. The results are shown in FIG. FIG. 2A shows the photocurrent of the device before the heat treatment, and FIG. 2B shows the photocurrent after the heat treatment. Thus, an approximately 3-fold increase was seen.

Also, when commercially available PPS with a large degree of polymerization was used as the evaporation source, the result of mass spectrometric analysis of the evaporated molecules was that the molecular weight was
It was found that the pentamer of 40 evaporated and adhered to the substrate. Since such a molecule forms a ring, it is considered that the crystallinity in the long chain direction of the molecule is lowered and the photocurrent is reduced.

Example 2 Similar to Example 1, as an example of containing a phenylene group having a substituent at a position other than the para-position of a phenylene group on a platinum first electrode formed by a sputtering method on a glass substrate,
A PPS derivative, poly (2,6-diethyl-1.4-phenylene sulfide) (hereinafter referred to as PDPS), was formed into a film by a vapor deposition method.

The raw material powders of PDPS and PPS were synthesized by the method of Tsuchida et al. (Proceedings of the 56th Spring Meeting of the Chemical Society of Japan, 1VIA03, 1VIA04). The degree of polymerization can be controlled by the oxidizing agent used in the synthesis, the acidity thereof, the reaction time, and the like.

Similar to Example 1, the raw material powders having different degrees of polymerization synthesized were used to form a film by the vapor deposition method. In the raw material powder of this example, the degree of polymerization of the raw material powder was about 4 and 10 for both the PDPS and PPS for two kinds of oxidizing agents, Lewis acid, AlCl ₃ and SbCl ₅ . This raw material powder was formed into a film having a thickness of 0.1 μm as a photoconductive layer by a vapor deposition method.

The photoelectric conversion efficiency of the thus obtained photovoltaic device was measured under the same conditions as in Example 1. As a result, the open-circuit voltage was 0.5 V, the short-circuit current was 1.6 × 10 ^-8 A / cm ^2, and the short-circuit current was also greatly improved. The FF was 0.31 and the conversion efficiency was 1.5%.

Example 3 A substrate in which a Nesa film of 0.1 μm was formed as a transparent electrode on a glass substrate was placed in a parallel plate type capacitively coupled plasma CVD apparatus having a 6-inch discharge electrode, and the inside of a reaction vessel was 5 × 10 ^−. After evacuation to ⁶ Torr or less, the substrate was heated and controlled to a constant temperature in the temperature range of 150 to 200 ° C. Add SiH ₄ gas into the reaction vessel.
50sccm, H ₂ containing ₂ to 5ppm of PH ₃ mixed and introduced 250sccm,
The pressure inside the container was controlled to 0.2 to 1.0 Torr, a high frequency of 13.56 MHZ was formed under the condition of an electric power of 40 to 80 W, and an a-Si: H layer was formed as a photoconductive layer of 0.1 μm.

Then, a PPS vapor deposition film was formed on the a-Si: H layer by vacuum vapor deposition using the raw material powder having a degree of polymerization of 8 in the same manner as in Example 1 to obtain a thickness of 0.1 μm.
m were laminated. Further, it was placed in a heat treatment furnace and subjected to heat treatment in an oxygen atmosphere. The heating temperature was controlled to a melting point of −2 ° C., and each heating treatment was performed.

After the heat treatment, platinum was formed as a second electrode on the PPS vapor deposition film by vapor deposition to obtain a photovoltaic element.

When this photovoltaic device was irradiated with 150 lux of a white fluorescent lamp from the glass substrate on the a-Si: H layer side, the open-ended voltage was 0.5.
V, short circuit current 8 × 10 ^-6 A / cm ² , FF 0.53, conversion efficiency
It was 3.2%.

Example 4 When a heat treatment was performed after forming the photoconductive layer, DDQ (2,3-dichloro-
5,6-dicyano-p-benzoquinone) was added. The PPS film as a raw material was heat-treated in an oxygen atmosphere under the same conditions as in Example 3 with an addition amount of 6 to 0.001 mol% and a film thickness of 0.5 μm to obtain a photovoltaic element.

In this way, the PPS deposited film with the electron acceptor added further decreased the internal resistance and increased the short-circuit current.

When the fluorescent lamp of 150 lux was irradiated, the open end voltage was 0.5 V and the short circuit current was 8 × 10 ^-8 A / cm ² .

In addition, when PPS not added is used, the short circuit current is 2
It was × 10 ^-8 A / cm ² .

Similar results were obtained when TCNE (tetracyanoethylene) was added at the same mol%.

Example 5 A nesa film was formed as a transparent electrode as a first electrode on a glass substrate, and a CdS film was formed to a thickness of 0.2 μm by a vacuum deposition method. This sample was further heat-treated in air at 400 ° C. for 20 minutes to deposit a PPS film as shown in Example 4 and heat-treated. After that, platinum is further formed as a second electrode,
A photovoltaic device was obtained.

Using this device, a glass substrate was irradiated with 150 lux of a fluorescent lamp to measure the photoelectric conversion efficiency. Open voltage 0.6
The V and short-circuit current are as high as 4.6 × 10 ^-6 A / cm ² . Also,
A device with an FF of 0.37 conversion efficiency of 1.4% was obtained.

Moreover, a highly efficient photovoltaic device was obtained even if Se was added to CdS.

Example 6 In the same manner as in Example 4, a PPS film was formed to a thickness of 0.1 μm by a vapor deposition method, and heat treatment was performed. Then, a Si (OH) ₂ Pc film having a thickness of 0.05 μm was formed by the same vacuum evaporation method, and an Al film was formed as a second electrode to have a transparent film thickness to obtain a photovoltaic device.

A fluorescent lamp of 150 lux was irradiated from above the Al electrode to measure the photoelectric conversion efficiency. Even if the electrode transmittance is not corrected, an open-circuit voltage of 0.6 V and a short-circuit current of 4 × 10 ^-8 A / cm ² are obtained, and FF0.36
Then, if the transmittance was corrected, a conversion efficiency of 2.5% was obtained.

Example 7 As in Example 1, a substrate was used in which a platinum electrode was formed on a mirror-polished glass substrate by sputtering to have a film thickness of 0.1 μm. Such a substrate was placed in a substrate holder of a vacuum vapor deposition apparatus, and the residual pressure was exhausted to 10 ^-5 Torr or less. Then, the poly (p-phenylene) selenide (hereinafter referred to as PPSe) powder is heated in a state of being heated to 50 to 150 ° C. to be 0.1 μm.
m PPSe vapor deposition film was obtained. On this film, Al was thinly deposited as a second electrode as a transparent electrode to form a photovoltaic element. The characteristics of this device were different from PPS, and a large short-circuit current was obtained even under a fluorescent lamp. When light was irradiated using fluorescent light of 150 lux, the open-circuit voltage was 0.5 V and the short-circuit current was 6.3.
A large value was obtained as compared with PPS, which was × 10 ^-8 A / cm ² .

On the other hand, according to the present invention, a 0.1 μm PPSe film was deposited and then heat-treated in oxygen at −200 ° C. for 1 to 5 hours. After the heat treatment, the Al electrode was thinly formed in the same manner as the transparent electrode, and the photoelectric conversion characteristics were measured in the same manner. The characteristics of this element are
The open-circuit voltage was 0.5 V, the short-circuit current was 9.6 × 10 ^-8 A / cm ^2, and the short-circuit current was improved. The FF was 0.35, and the conversion efficiency was 2.4% when the electrode transmittance was taken into consideration.

When the composition of PPSe of this photovoltaic device was analyzed, the composition ratio of O atoms contained in the layer to C atoms was 1.2a.
It was tm%.

Example 8 A nesa film was formed as a transparent electrode as a first electrode on a glass substrate in the same manner as in Example 5, and as shown in Example 7,
A PPSe film is deposited and then As ₂ S is deposited by vacuum deposition.
e ₂ film 0.2μm is formed, platinum is formed as the second electrode,
A photovoltaic device was obtained.

Using this device, a glass substrate was irradiated with 150 lux of a fluorescent lamp to measure the photoelectric conversion efficiency. Open voltage 0.6
The V and short-circuit current is as high as 5.3 × 10 ^-6 A / cm ² . Also,
A device with an FF of 0.37 conversion efficiency of 2.4% was obtained.

A similar effect was observed with poly (p-phenylene) telluride in which Se was replaced with Te.

Also, high conversion efficiency was confirmed even when a heterojunction with another semiconductor material was formed as in Examples 3 and 8.

EFFECTS OF THE INVENTION According to the present invention, it is possible to obtain a photovoltaic device that includes a photoconductive layer having high carrier generation efficiency, high carrier life and mobility, and that realizes high photoelectric conversion efficiency.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a photovoltaic device according to one embodiment of the present invention, and FIG. 2 is a graph showing the effect of improving photocurrent at each wavelength in one embodiment of the present invention. 1 ... Support, 2 ... First electrode, 3 ... Photoconductive layer, 4 ...
… Second electrode.

Claims (7)

[Claims] 1. A photovoltaic device using a photoconductive layer that generates carriers by photoexcitation, wherein at least a part of the photoconductive layer contains a linear polymer layer having p-phenylene as a main component. in the infrared absorption spectrum of the linear polymer layer, the intensity of the absorption spectra for CH out-of-plane deformation vibration of a benzene ring having para-disubstituted group in the vicinity 825Cm ^-1, monosubstituted in the vicinity 750 cm ^-1 A photovoltaic device, wherein the ratio of the absorption spectrum of the CH out-of-plane bending vibration of the benzene ring having a group to the intensity of the absorption spectrum is 0.9 or more and 2.5 or less. 2. A linear compound polymer layer in which at least a part of the photoconductive layer has p-phenylene and has a VI _b group element in the para position, and which comprises S, Se and Te as the VI _b group element. The photovoltaic device according to claim 1, comprising at least one selected. 3. The polymer layer in the photoconductive layer contains O atom,
The ratio of the number of O atoms contained in the polymer to the number of C atoms is
The photovoltaic device according to claim 1, characterized in that it is 0.1 to 5 atm%. 4. The photovoltaic device according to claim 1, wherein an electron acceptor is added to the polymer layer in the photoconductive layer. 5. The polymer layer in the photoconductive layer is mainly composed of a linear polymer layer having p-phenylene, and the p-phenylene has a substituent at a position other than the para position. The photovoltaic device according to claim 1. 6. The method of manufacturing a photovoltaic device according to claim 1, wherein the step of forming the polymer layer in the photoconductive layer is a linear polymer having p-phenylene,
A method for producing a photovoltaic device, characterized in that the polymer layer is formed by a vapor deposition method using an oligomer having an average degree of polymerization of 4 to 10 as an evaporation source. 7. The process according to claim 6, wherein in the step of forming the polymer layer in the photoconductive layer, heat treatment is performed at a temperature lower than the melting point of the polymer layer after forming the polymer layer. Method for manufacturing photovoltaic device of.