JP2001274429A - Hybrid thin film photoelectric converter and producing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly reliable hybrid thin film photoelectric converter showing an almost fixed photoelectric conversion characteristic without depending on a measuring method. SOLUTION: This hybrid thin film photoelectric converter is provided with a transparent electrode 2, a noncrystalline photoelectric converting unit 3, a crystalline photoelectric converting unit 4, and a rear electrode 5 successively laminated on a transparent insulating substrate 1. The crystalline unit 4 is provided with a p-type layer 4p, a crystalline i-type photoelectric converting layer 4i and an n-type layer 4n successively deposited by a plasma CVD method. The p-type layer 4p provided in the crystalline unit 4 has a crystallization factor greater than 85% on the interface with the crystalline i-type photoelectric converting layer 4i, the crystalline i-type photoelectric converting layer 4i has a crystal structure containing a prismatic crystal extended in the direction of the thickness, and that prismatic crystal is extended in <110> preferential crystal direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor thin-film photoelectric conversion device, and more particularly to improvement in reliability of a hybrid silicon-based thin-film photoelectric conversion device.

[0002]

2. Description of the Related Art In general, a semiconductor thin-film photoelectric conversion device has a first electrode, at least one semiconductor thin-film photoelectric conversion unit, and a second thin-film photoelectric conversion unit which are sequentially laminated on an insulating substrate at least on the surface.
Includes electrodes. Then, one photoelectric conversion unit includes an i-type layer sandwiched between a p-type layer and an n-type layer. The i-type layer occupying most of the thickness of the photoelectric conversion unit is a substantially intrinsic semiconductor layer, and the photoelectric conversion action mainly occurs in the i-type layer.

Therefore, regardless of whether the p-type and n-type conductive layers included therein are amorphous or crystalline, a photoelectric conversion unit having an amorphous i-type photoelectric conversion layer has an amorphous structure. A unit in which the i-type layer is crystalline is called a crystalline unit. In the specification of the present application, the term “crystalline” also means a material that partially includes an amorphous state, as generally used in the technical field of a thin-film photoelectric conversion device.

On the other hand, the p-type or n-type conductive layer plays a role of generating a diffusion potential in the photoelectric conversion unit, and one of the important characteristics of the photoelectric conversion device depends on the magnitude of the diffusion potential.
The value of the open-circuit voltage is also affected. However, these conductive type layers are inactive layers that do not directly contribute to photoelectric conversion, and light absorbed by impurities doped in the conductive type layers is a loss that does not contribute to power generation. Therefore, on the assumption that the conductive type layer generates a necessary diffusion potential,
It is desired that the thickness be as thin as possible.

[0005] When a thin-film photoelectric conversion device is formed on a transparent insulating substrate such as a glass plate, the substrate can serve as a cover glass for protecting the surface of the photoelectric conversion device. In many cases, a p-type layer having a relatively large bandgap, an i-type photoelectric conversion layer, and an n-type layer having a relatively small bandgap are stacked on a glass substrate via a transparent electrode.

As a method of improving the conversion efficiency of a thin film photoelectric conversion device, there is a method of stacking two or more photoelectric conversion units to form a tandem type. In this method,
A front unit including a photoelectric conversion layer having a large band gap is disposed on the light incident side of the photoelectric conversion device, and a rear band unit having a smaller band gap (for example, Si-G
By arranging the rear unit including the photoelectric conversion layer (of the e-alloy), it is possible to perform photoelectric conversion over a wide wavelength range of incident light, thereby improving the conversion efficiency of the entire device. Among tandem-type thin film photoelectric conversion devices, a device in which an amorphous photoelectric conversion unit and a crystalline photoelectric conversion unit are stacked is referred to as a hybrid thin film photoelectric conversion device.

For example, the wavelength of light that can be photoelectrically converted by i-type amorphous silicon is up to about 800 nm on the long wavelength side, while i-type crystalline silicon has a longer wavelength of about 11 nm.
It is possible to photoelectrically convert light having a wavelength of about 00 nm. Therefore, when a hybrid thin-film photoelectric conversion device is formed on a glass substrate, usually, a transparent electrode, an amorphous unit, a crystalline unit, and a back electrode are laminated on the glass substrate in this order.

[0008]

SUMMARY OF THE INVENTION Such a hybrid thin film photoelectric conversion device is a single type thin film photoelectric conversion device including either a single amorphous photoelectric conversion unit or a single crystalline photoelectric conversion unit. In comparison, it can exhibit significantly higher photoelectric conversion efficiency.

However, recently, the present inventor has found that although the cause is unknown at this time, the photoelectric conversion characteristic value obtained by measuring the hybrid thin-film photoelectric conversion device varies depending on the measurement method. . This means that the hybrid thin-film photoelectric conversion device, in which the photoelectric conversion characteristic value obtained by a certain measurement method is displayed as the nominal performance, cannot be relied on as to whether the hybrid thin-film photoelectric conversion device can perform the nominal performance in its actual use state. Means that. The fact that the obtained photoelectric conversion characteristic value fluctuates depending on the measurement method does not occur in a single-type thin-film photoelectric conversion device or a tandem-type thin-film photoelectric conversion device including only a plurality of amorphous units. is there.

Generally, a photoelectric conversion characteristic value of a photoelectric conversion device is measured by a method as shown in a simplified circuit diagram of FIG. In FIG. 3, the thin-film photoelectric conversion device 11 has properties as a diode based on a pin semiconductor junction included therein, and when receiving the light L, a reverse direction opposite to a forward direction which is a rectifying direction of the diode. Output current. The photoelectric conversion device 11 is connected in series with an external voltage source 12 and an ammeter 13, and these constitute a closed loop. Conventionally, as the external voltage source 12, a variable DC (direct current) voltage source capable of applying a voltage of an arbitrary value to the diode 11 in the forward direction is used.

In general, when the photoelectric conversion device 11 is irradiated with the light L from the solar simulator, the forward voltage of the diode 11 is swept from the zero potential to the positive potential from the external DC voltage source 12 to the DC voltage. Or apply
Alternatively, the output current value of the photoelectric conversion device 11 at the time of 0 potential is measured as the short-circuit current value Jsc by sweeping from the positive potential larger than the expected open-end output voltage to the 0 potential and applying a DC voltage. , Open end voltage value Voc
Is measured from an externally applied voltage balanced to make the output current zero. However, the present inventor has obtained a hybrid thin-film photoelectric conversion device as a measured value depending on the direction in which the externally applied voltage is swept, the speed of the voltage sweep, and the pre-bias voltage before the start of the voltage sweep. It was found that the obtained photoelectric conversion characteristic value fluctuated.

Therefore, the present inventor has proposed an external DC voltage source 12.
That can apply an arbitrary voltage to the diode 11 in both the forward direction and the reverse direction, and systematically change the measuring method to obtain the photoelectric conversion characteristics of one conventional hybrid thin-film photoelectric conversion device. The variation of the value was examined. The result is shown in the graph of FIG.

In the graph of FIG. 4, the horizontal axis represents the output voltage (V) of the photoelectric conversion device 11, and the vertical axis represents the output current density (mA / cm ² ). The solid curve in the graph indicates that the pre-bias voltage of -2.5 V (reverse voltage for the diode) was applied for 5 minutes or more, and then 100 ms.
The irradiation of simulated sunlight having a spectral distribution of AM1.5 and an energy density of 100 mW / cm ² from the solar simulator is started within ec, and from +2.5 V (forward voltage to the diode) to −2.5 V.
The measurement results when the external applied voltage is swept in 5 seconds are shown.

[0014] Similarly, the dotted curve shows that the pre-bias voltage of -2.5 V is applied for more than 5 minutes, and the curve from -2.5 V to -2.5 V is applied.
The measurement result when the voltage sweep is performed in 20 seconds to 2.5 V is shown. The broken line curve is -2.5V
-2.5V after applying the pre-bias voltage of 5 minutes or more
It shows the measurement results when a voltage sweep is performed from 20 to +2.5 V in 20 seconds. Further, the one-dot chain line shows the measurement results when the voltage was swept from +2.5 V to -2.5 V in 1.5 seconds after the pre-bias voltage of +2.5 V was applied for 5 minutes or more.

As can be seen from FIG. 4, the short-circuit current density J
As sc, almost 10 mA without depending on the measurement method
/ Cm ^2, but the open-end voltage value Voc varies from 1.22 V to 1.34 V depending on the measurement method. Along with this, the photoelectric conversion efficiency value at the maximum output also
It fluctuates from 8.2% to 9.1%.

In view of such problems that the present inventors have found and confirmed, the present invention provides a highly reliable hybrid thin-film photoelectric conversion device that exhibits a substantially constant photoelectric conversion characteristic value without depending on a measuring method. It is intended to be.

[0017]

According to the present invention, there is provided a hybrid thin-film photoelectric conversion device comprising a transparent electrode, an amorphous photoelectric conversion unit, a crystalline photoelectric conversion unit, and a back surface which are sequentially laminated on a transparent insulating substrate. The crystalline unit includes an electrode, and the crystalline unit includes a p-type layer, a crystalline i-type photoelectric conversion layer, and an n-type layer sequentially deposited by a plasma CVD method, and the p-type layer included in the crystalline unit includes a crystalline i-type. The crystalline i-type photoelectric conversion layer has a crystal structure including columnar crystals extending along its thickness direction, having a crystallization fraction of greater than 85% at the interface with the photoelectric conversion layer. 110> extending along the preferred crystal direction. The p-type layer included in the crystalline unit more preferably has a crystallization fraction of 95% or more at the interface with the crystalline i-type photoelectric conversion layer.

In the method of manufacturing such a hybrid thin film photoelectric conversion device, the p-type layer and the crystalline i-type layer included in the crystalline unit are formed by a plasma using a mixed gas containing at least a silane-based source gas and a hydrogen diluent gas. The p-type layer deposited by CVD and contained in crystalline units is 400
It is characterized in that it is deposited under a gas pressure of less than Pa (3 Torr) and the crystalline i-type layer is deposited under a gas pressure of 667 Pa (5 Torr) or more. In addition, during the deposition of the p-type layer included in the crystalline unit, it is preferable that the mixing ratio of the hydrogen diluent gas to the silane-based source gas is made larger than 100 times.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Based on the following various experimental examples,
Embodiments that can exhibit the effects of the present invention will be clarified.

First, when starting various experiments,
Japanese Unexamined Patent Application Publication No. 11-110, which is referred to as a method for forming a crystalline photoelectric conversion unit included in a hybrid type thin film photoelectric conversion device
145499 indicates that the pressure in the plasma reaction chamber is 400 Pa
(3 Torr) or more and the silane gas and its 50
By using a hydrogen dilution gas with a mixing ratio of twice or more,
It discloses that a high quality crystalline silicon-based photoelectric conversion unit can be deposited at a high speed. And, it is more preferable that the pressure in the reaction chamber is 667 Pa (5 Torr) or more.

Therefore, the present inventor produced a hybrid thin-film photoelectric conversion device as shown in the schematic sectional view of FIG. 1 under the method and conditions described below.

That is, in the first experimental example, a glass substrate 1 having a TCO (transparent conductive oxide) electrode 2 having a thickness of about 600 nm formed on one main surface was prepared. TC
An amorphous silicon-based photoelectric conversion unit 3 having a thickness of about 300 nm was deposited on the O electrode 2 by plasma CVD. The amorphous photoelectric conversion unit 3 includes a p-type layer 3p, an amorphous photoelectric conversion layer 3i, and an n-type layer 3n. These layers are formed under well-known and ordinary conditions when forming an amorphous unit. Deposited.

A crystalline photoelectric conversion unit 4 is placed on the amorphous unit 3 under a substrate temperature of 150 ° C., a reaction chamber pressure of 667 Pa (5 Torr), and an RF (high frequency) power of 100 mW / cm ^2. It was formed by plasma CVD. The p-type layer 4p included in the crystalline unit 4 has 20 sccm of silane and 8000 sc of hydrogen.
using 20 sccm of a diborane-containing gas containing diborane hydrogen-diluted to 5000 ppm
Deposited to a thickness of. The crystalline i-type photoelectric conversion layer 4i was deposited to a thickness of 2.5 μm using 20 sccm of silane and 1500 sccm of hydrogen. The crystalline i-type photoelectric conversion layer 4i thus formed has a crystal structure including columnar crystals extending along the thickness direction, and the columnar crystals are <1
10> It extends along the preferred crystal direction. The n-type layer 4n is made of 20 sccm of silane and 6000 s of hydrogen.
ccm and 80 sccm of a phosphine-containing gas containing phosphine diluted to 5000 ppm with hydrogen.
Deposited to a thickness of 0 nm.

On the crystalline photoelectric conversion unit 4, a TCO layer 5 t having a thickness of 80 nm and a thickness 400
A 5 nm silver layer was deposited by sputtering and evaporation, respectively. The TCO layer 5t can function to maintain the light reflectivity of the silver layer 5m high and to prevent silver atoms from diffusing into the photoelectric conversion units 4 and 3.

With respect to the hybrid thin-film photoelectric conversion device according to the first experimental example thus manufactured, a pre-bias voltage of +2.5 V was set to 1 in the same measurement as in FIG.
When a voltage sweep is performed for 1.5 seconds from +2.5 V to -2.5 V after application for 0 minutes or more, 1.
An open-end voltage value of 22 V was obtained. On the other hand, after applying a pre-bias voltage of -2.5 V for 10 minutes or more, +2.5 V
When the voltage was swept from 1.5 to -2.5 V in 1.5 seconds, an open-end voltage value of 1.36 V was obtained. In other words, the hybrid thin-film photoelectric conversion device according to the first experimental example exhibits an open-circuit voltage value that changes by as much as 0.14 V depending on the measurement method, and has to be said to have poor reliability.

Therefore, the present inventor, when fabricating more hybrid thin-film photoelectric conversion devices as shown in FIG. , The thickness of the crystalline photoelectric conversion unit 4 is in the range of 1.0 to 5.0 μm, and the pressure of the plasma reaction chamber during the deposition of the p-type layer 4p included in the crystalline unit 4 is 133 to 1330 Pa. (1-10T
A number of experiments were performed with various changes in the range of (orr) and other conditions being the same as those of the first experimental example.

With respect to the hybrid thin-film photoelectric conversion devices obtained in these experiments, photoelectric conversion characteristic values were measured in the same manner as in the case of FIG. As a result, regarding the change in the thickness between the amorphous unit 3 and the crystalline unit 4 included in the hybrid type thin film photoelectric conversion device, the variation in the photoelectric conversion characteristic value depending on the measurement method has a systematic relationship. Not observed. Also, the i-type photoelectric conversion layer 4i included in any of the crystalline units 4 had a columnar crystal structure along the thickness direction.

However, regarding the change of the pressure in the reaction chamber during the deposition of the p-type layer 4p included in the crystalline unit 4, it is found that the fluctuation of the photoelectric conversion characteristic value depending on the measurement method has a systematic relationship. Was issued. The result is shown in FIG.

In the graph of FIG. 2, the horizontal axis represents the pressure (× 133 Pa: Torr) of the reaction chamber when the p-type layer 4p included in the crystalline unit 4 is deposited. On the other hand, the vertical axis of this graph indicates +2.5 V before applying 10 seconds or more after applying the pre-bias voltage of +2.5 V for 10 minutes or more.
From the measured Voc value when a voltage sweep was performed from 1.5 V to -2.5 V in 1.5 sec, 1.5 sec from +2.5 V to -2.5 V after applying a pre-bias voltage of -2.5 V
Represents the open-ended voltage fluctuation value ΔVoc (V) obtained by subtracting the measured Voc value when the voltage sweeps.

As is clear from this graph, when the reaction chamber pressure at the time of forming the p-type layer 4p included in the crystalline unit 4 is 400 Pa (3 Torr) or more, the open-end voltage fluctuation of the hybrid thin-film photoelectric conversion device is obtained. It can be seen that the absolute value of the value ΔVoc increases and its reliability decreases. On the other hand, the deposition pressure of the p-type layer 4p is 400 Pa (3 Torr).
When the value is less than 0.002 V, the open-end voltage fluctuation value ΔVoc is almost 0 (which is considered to be a measurement error range), which indicates that a highly reliable hybrid thin-film photoelectric conversion device can be obtained.

In view of the fact that the p-type layer 4p included in the crystalline unit 4 has a significant effect on the open-end voltage fluctuation value ΔVoc of the hybrid thin-film photoelectric conversion device, the present inventor further described the following. An experiment was attempted. That is. Under the same deposition conditions as described above for the p-type layer 4p included in the crystalline unit 4, a 20-nm-thick p-type layer was directly deposited on the glass substrate.

For the p-type layer on this glass substrate, 25
The component ratio between amorphous silicon and crystalline silicon, that is, the crystallization fraction (also referred to as crystallinity) was measured using a spectroscopic ellipsometer in the wavelength range of 0 to 1200 μm. As a result, it was found that the crystallinity of the p-type layer was variously different between the thickness of 10 nm on the glass substrate side and the thickness of 10 nm on the growth surface side. Such a result is shown in Table 1.

[0033]

[Table 1]

As can be seen from Table 1, even if the film forming pressure of the p-type layer changes in the range of 1.0 to 13.0 (× 133 Pa: Torr), the crystallization of the p-type layer on the glass substrate side. The degree of crystallinity varies within a relatively narrow range of 65 to 80%, but the crystallinity on the growth surface side varies over a much larger range. That is, when the film forming pressure on the growth surface side of the p-type layer is about 400 Pa (3 Torr) or less, the crystallinity is about 95% or more and 667 Pa (5 Torr).
Before and after r), the crystallinity is about 70 to 80%, and at about 1333 Pa (10 Torr) or more, the crystallinity is about 40% or less.

Considering these facts and the results of FIG. 2, in order to obtain a highly reliable hybrid thin-film photoelectric conversion device in which the open-circuit voltage fluctuation value ΔVoc depending on the measurement method is small, It is desired that the p-type layer 4p included in the crystalline unit 4 has a degree of crystallinity greater than 85% at the interface with the crystalline i-type photoelectric conversion layer 4i,
It is believed that having a crystallinity of 95% or more is more preferred.

In general, the crystallinity of a silicon layer deposited by plasma CVD is also affected by the underlying layer, so the crystallinity of the p-type layer 4p included in the crystalline unit 4 is the underlying layer. It is considered that the influence of the crystallinity of the n-type layer 3n included in the amorphous unit 3 also exists. However, since the crystallinity of the n-type layer 3n included in the amorphous unit 3 is generally not considered to be so high, the film forming pressure and the crystallinity in the p-type layer 4p included in the crystalline unit 4 are considered. Is presumed to have the same tendency as in the p-type layer deposited on the glass substrate.

[0037]

As described above, according to the present invention, it is possible to provide a highly reliable hybrid thin-film photoelectric conversion device exhibiting a substantially constant photoelectric conversion characteristic value without depending on the measuring method.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an example of a hybrid thin-film photoelectric conversion device according to an embodiment of the present invention.

FIG. 2 shows a hybrid thin-film photoelectric conversion device.
4 is a graph showing a relationship between a film forming pressure of a p-type layer included in a crystalline unit and an open-end voltage fluctuation value depending on a measurement method.

FIG. 3 is a simplified circuit diagram for explaining a method of measuring a photoelectric conversion characteristic value of a photoelectric conversion device.

FIG. 4 is a graph showing measurement method dependence of a photoelectric conversion characteristic value in a hybrid thin-film photoelectric conversion device according to the prior art.

[Explanation of symbols]

Reference Signs List 1 glass substrate, 2 TCO electrode, 3 amorphous photoelectric conversion unit, 3 p p-type layer, 3 i amorphous i-type photoelectric conversion layer, 3 n n-type layer, 4 crystalline photoelectric conversion unit, 4 p
p-type layer, 4i crystalline i-type photoelectric conversion layer, 4n n-type layer, 5 back electrode, 5t TCO layer, 5m metal layer.

Claims (4)

[Claims] 1. A transparent electrode, an amorphous photoelectric conversion unit, a crystalline photoelectric conversion unit, and a back electrode sequentially laminated on a transparent insulating substrate, wherein the crystalline photoelectric conversion units are sequentially deposited by a plasma CVD method. A p-type layer, a crystalline i-type photoelectric conversion layer, and an n-type layer, wherein the p-type layer contained in the crystalline unit has a crystallized fraction greater than 85% at an interface with the crystalline i-type photoelectric conversion layer. The crystalline i-type photoelectric conversion layer has a crystal structure including columnar crystals extending along the thickness direction thereof, and the columnar crystals have a <11
0> A hybrid thin-film photoelectric conversion device extending along a preferred crystal direction. 2. The method according to claim 1, wherein the p-type layer included in the crystalline unit has a crystallization fraction of 95% or more at the interface with the crystalline i-type photoelectric conversion layer.
3. The hybrid thin-film photoelectric conversion device according to item 1. 3. The method for manufacturing a hybrid thin-film photoelectric conversion device according to claim 1, wherein the p-type layer and the crystalline i-type layer included in the crystalline unit are at least silane-based. The p-type layer is deposited by plasma CVD using a mixed gas containing a source gas and a hydrogen dilution gas, and the p-type layer contained in the crystalline unit is 400 Pa (3
A method according to claim 1, wherein the crystalline i-type layer is deposited under a gas pressure of less than 667 Pa (5 Torr). 4. The method according to claim 3, wherein during the deposition of the p-type layer included in the crystalline unit, the mixture ratio of the hydrogen dilution gas to the silane-based source gas is set to be larger than 100 times. Production method.