JP2755670B2 - Photoelectric conversion element and photovoltaic device - Google Patents

Description

Description: (a) Industrial application field The present invention relates to a photoelectric conversion element that generates an electromotive force by receiving light irradiation, and a photovoltaic device formed by connecting a plurality of the photoelectric conversion elements in series.

(B) Conventional technology The light-receiving surface electrode film in a photovoltaic device that generates an electromotive force upon receiving light irradiation may be translucent to cause light irradiation on a semiconductor photoactive layer that performs a photoelectric conversion action. preferable.
_{Conventionally, In 2 O 3, SnO 2} , translucent conductive oxide represented by ITO or the like is an oxide of order Teisu the translucent light-receiving surface side electrode is indium (In), tin (Sn) (hereinafter TCO). The electrode made of this TCO has a sheet resistance of about 30 to 50 Ω / □, which is more than three orders of magnitude higher than a metal material such as aluminum having the same film thickness. ) Occurs,
This may cause a reduction in current collection efficiency.

Accordingly, the applicant of the present application has proposed a high-resistance light-receiving surface electrode film.
Japanese Patent Application Laid-Open Nos. 61-20371 and 61-86955 have filed applications as structures for reducing the resistance loss due to the light-receiving surface electrode film despite the use of TCO. This photovoltaic device includes a light receiving surface electrode film, a semiconductor film including a photoactive layer, a first back electrode film, an insulating film, and a second back electrode film having a lower resistance than the light receiving surface electrode film when viewed from the light incident side. The second back electrode film is overlapped with the second back electrode film by reaching the light receiving surface electrode film at a plurality of locations in the light receiving region by passing through the contact hole whose inner periphery is surrounded by the insulating film. And the light receiving surface electrode film is electrically coupled.

(C) Problems to be Solved by the Invention By the way, in using a photovoltaic device, the sheet resistance of the light-transmitting light-receiving surface electrode film, in other words, the thickness thereof affects power loss.

Therefore, the present invention optimizes the thickness of the light-transmitting light-receiving surface electrode film and suppresses power loss.

(D) Means for Solving the Problems The present invention provides a light-receiving area by overlapping a light-transmitting light-receiving surface electrode film, a semiconductor film including a photoactive layer, a first back electrode film, an insulating film, and a second back electrode film. A plurality of connection points in the photoelectric conversion element in which the second electrode film penetrates the insulating film and is electrically coupled to the light-receiving surface electrode film, where q is an elementary charge and k is a Boltzmann constant. , The thickness of the light-receiving surface electrode film under predetermined conditions, T (absolute temperature), i _ph (photocurrent density), i ₀ (reverse saturation current density), R _s (series resistance) R _sh
The film thickness determined from the value of R _st (sheet resistance) at which the output power based on the output current calculated by the following equation using the values of (shunt resistance) and n (n value of the diode characteristic) is approximately the maximum. It is characterized by having.

i (r) = i _ph −i ₀ [exp ｛q (V (r) + R _s i
(R)) / nkT｝ −1] − (V (r) + R _s i (r)) / R _sh dV (r) / dr = I (r) · R _st / 2πr where I _out : 1 Output current at connection point i (r): current amount generated in minute area at radius r point I (r): total current amount flowing in the direction of contact hole in ring-shaped area at radius r point V (r): radius r point R: the radius of a circle having the same area as the square corresponding to the arrangement interval of the connection points R ₀ : the radius of the connection points Further, the photoelectric conversion elements described in item 1 are connected to one of the photoelectric conversion elements adjacent to each other. The one back electrode film and the other back electrode film are electrically connected in series by being coupled to the semiconductor film on the back side.

(E) Function According to the present invention, the film thickness of the light receiving surface electrode film is set to a film thickness determined from a sheet resistance value at which an output voltage based on an output current calculated by a predetermined relational expression is substantially maximum. As a result, a photoelectric conversion element and a photovoltaic device which are optimized and have excellent output characteristics can be obtained.

(F) Embodiment FIG. 1 is a partial cross-sectional perspective view of a main part of a first embodiment of a photovoltaic device of the present invention viewed obliquely from the back side with respect to the light incident direction. As shown, a transmissive light-receiving surface electrode film such as TCO (1), a semiconductor film mainly composed of amorphous silicon including a photoactive layer of a semiconductor junction such as a pin junction and a pn junction parallel to the film surface (2), ohmic A first back electrode film (3) made of metal, an insulating film (4), and a second back electrode film (5) made of a metal having lower resistance than the light receiving surface electrode film (1) are superimposed to form a second back electrode. The film (5) penetrates the insulating film (4), the first back electrode film (3), and the semiconductor film (2) at a plurality of positions in the light receiving region, and the inner periphery is surrounded by the insulating film (4). By reaching the light-receiving surface electrode film (1) through the circular contact hole (6), the light-receiving surface electrode film (1) is electrically connected to the light-receiving surface electrode film (1). A plurality of unit photovoltaic bound to (SC
₁ ) (SC ₂ ) (SC ₃ ) ... is replaced by each unit photoelectric conversion element (SC ₁ )
The light receiving surface electrode films (1) of (SC ₂ ) and (SC ₃ ) are provided on a translucent insulating substrate (7) such as glass serving as a support and a light receiving surface protector with a separation distance d. I have.

Then, each unit photoelectric conversion element (SC ₁ ) (SC ₂ ) (SC ₃ )
The light-receiving surface electrode film (1) and the first back electrode film (3) of the element adjacent to each other are connected to each photoelectric conversion element (SC ₁ ) (SC ₂ ) (SC ₃ ).
The first back electrode film (in the portion opened by performing, for example, laser beam irradiation or etching) on the back surface side of the semiconductor film (2) from the side of the insulating film (4) without directly overlapping in the adjacent space portion of 3), the second back electrode film (5) of the adjacent element extends and is buried, so that the adjacent unit photoelectric conversion elements (SC ₁ ) (SC ₂ ) (SC ₃ )
Are electrically connected in series.

By the way, in the photovoltaic device having such a structure, the diameter of the contact hole (6) was considered before determining the thickness of the light receiving surface electrode film (1).

FIG. 2 shows the relationship between the diameter of the contact hole (6) and the contact resistance of this portion, and FIG. 3 shows the relationship between the diameter of the contact hole (6) and the maximum output of the photovoltaic device. When the size of the contact hole (6) is reduced, the ineffective area in the light receiving region is also reduced. However, workability and workability are poor, and when the contact hole (6) is further reduced, a contact hole for collecting current is formed. (6)
The contact resistance between the light-receiving surface electrode film (1) and the second back electrode film (5) at the center of (2) increases (see FIG. 2), and the resistance loss is not reduced.

On the other hand, if the contact hole (6) is enlarged to facilitate workability and workability, the ineffective area in the light receiving region becomes large, and the maximum output of the photovoltaic device is reduced (see FIG. 3).

Therefore, in the photovoltaic device as described above, in order to obtain the maximum output, the diameter of the contact hole (6) is set to an appropriate value, in this embodiment, 0.2 mm.

Thereafter, in the present invention, the thickness of the light receiving surface electrode film (1) is determined from the sheet resistance of the light receiving surface electrode film (1) by using the diameter of the contact hole (6) and increasing the output of the photovoltaic device. did. Here, in determining the film thickness of the light-receiving surface electrode film (1), the output current in the contact hole (6) is calculated, and the film thickness is calculated from the sheet resistance value at which the output power becomes substantially maximum based on this. Decided.

The current collected by each contact hole (6) is
It occurs inside a circle having a radius R. This circle is drawn around the contact hole (6) so as to be in contact with each other around each contact hole (6) and to have the same area as a square defined by the same area. Is also automatically determined.

The first expression below shows an output current I _out in one contact hole (6).

However, in the above equation, R: radius of a circle having the same area as the square corresponding to the arrangement interval of the contact holes (6) R0: radius of the contact holes (6) i (r): generated in a small area at a radius r point Current Amount The current amount i (r) is obtained by the following equations (2) and (3).

In the above equation, i _ph : photocurrent density i _o : reverse saturation current density v (r): voltage at radius r R _s : series resistance R _sh : shunt resistance n: n value of diode characteristics q: elementary charge k: Boltzmann's constant T: absolute temperature R _st : sheet resistance I (r): total amount of current flowing in the direction of the contact hole (6) in the ring-shaped region at radius r where q and k are constants, and T, The values of i _ph , i ₀ , R _s , R _sh , and n may be values obtained under predetermined conditions. The predetermined condition may be any condition, for example, a known latest photovoltaic power generation technology (published on July 1, 1984, Maki Shoten, 143
Page) standard measurement conditions for solar cells (AM1.5,100m
W / cm ² , 28 ° C.).

FIG. 4 shows the sheet resistance of the light-receiving surface electrode film (1) (that is, the sheet resistance of the light-receiving surface electrode film (1)).
FIG. 4 is a characteristic diagram showing a relationship between a film thickness) and a maximum output of a photovoltaic device.
The figure shows the results of calculating the output characteristics of the entire apparatus using the above equations, with 2 mm and a contact resistance of 15Ω. In addition,
In the figure, the solid line shows the characteristics of the present invention, and the broken line shows the characteristics of the conventional example. In each case, the photovoltaic device has the photoelectric conversion elements (SC ₁ ) (SC ₂ ) (SC ₃ ). It is 10cm x 10cm in size provided with 10 pieces.

As can be seen from the figure, there is an optimum value of the sheet resistance of the light receiving surface electrode film (1) in order to obtain the maximum output. Therefore, in manufacturing the photovoltaic device, high output can be achieved by setting the thickness of the light receiving surface electrode film (1) to a thickness determined from the optimum value of the sheet resistance. .

In the conventional example, when the sheet resistance is increased, the maximum output is greatly reduced. However, in the present invention, the maximum output is highest on the high sheet resistance side (that is, about 1000 °) as compared with the conventional example. Even if the sheet resistance increases by about one digit, the output decreases only by about several percent.

FIG. 5 is a partial cross-sectional perspective view of a main part of a second embodiment of the photovoltaic device of the present invention viewed obliquely from the rear side with respect to the light incident direction.

This embodiment is characterized in that the light incident direction is reversed as compared with the previous embodiment. That is, an insulating substrate (70) made of a metal plate (71) such as stainless steel or an aluminum plate having an insulating film (72) such as an enamel or a sealed alumina film on the surface is prepared. A metal second back electrode film (5) is divided and arranged for each of the elements (SC ₁ ) (SC ₂ ) (SC ₃ )... Then, an insulating film (4), a first back electrode film (3), and at least one A semiconductor film (2) including a photoactive layer having a semiconductor junction and a transparent light-receiving surface electrode film (1) such as TCO are laminated. At this time, the insulating film (4) is divided for each element (SC ₁ ) (SC ₂ ) (SC ₃ ).
A first back electrode film (3) of an adjacent element is bonded to the back electrode film (5). Semiconductor film (2), first back electrode film (3)
A contact hole (6) reaching the second back electrode film (5) at a plurality of positions in the light receiving region is formed in the insulating film (4) as in the first embodiment, and the inner wall of the contact hole (6) is It is covered with the insulating film (4). By burying the contact hole (6) with the light-receiving surface electrode film (1), the light-receiving surface electrode film (1) and the second back electrode film (5) are electrically coupled with each other, and The photoelectric conversion elements (SC ₁ ) (SC ₂ ) (SC ₃ ) are electrically connected in series on the back surface of the semiconductor film (2).

Also in the photovoltaic device having this structure, the thickness of the light-receiving surface electrode film (1) is calculated by calculating the output current in the contact hole (6) based on the above-mentioned three equations, as in the first embodiment. It is natural that the film thickness is determined from the sheet resistance value at which the output power based on the sheet resistance becomes substantially maximum.

In addition, each contact hole (6) is not limited to the circular shape as described above, but may be an arbitrary shape such as a square. In this case, for example, the current collected by each of the square contact holes (6) is a current generated in a square that is in contact with each other with each contact hole (6) as a center and divided by the same area. Therefore, the size of the contact hole (6) and the interval between the contact holes are determined by calculating the current generated in the square.

(G) Effect of the Invention The photoelectric conversion element and the photovoltaic device of the present invention are provided by setting the thickness of the light receiving surface electrode film to a value of a sheet resistance at which an output voltage based on an output current calculated by a predetermined relational expression becomes substantially maximum. Therefore, a photovoltaic device having optimal output characteristics can be provided.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional perspective view showing a main part of a first embodiment of the present invention, FIG. 2 is a characteristic diagram showing a relationship between a diameter of a contact hole and a contact resistance of this portion, and FIG. FIG. 4 is a characteristic diagram showing the relationship between the diameter of the photovoltaic device and the maximum output of the photovoltaic device. FIG. 4 is a characteristic diagram showing the relationship between the sheet resistance (that is, the film thickness) of the light receiving surface electrode film and the maximum output of the photovoltaic device. FIG. 5 is a partially sectional perspective view showing a main part of a second embodiment of the present invention.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-194370 (JP, A) JP-A-59-167056 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01L 31/04

Claims (2)

(57) [Claims] 1. A light-transmitting light-receiving surface electrode film, a semiconductor film including a photoactive layer, a first back electrode film, an insulating film, and a second back electrode film are superimposed on each other, and the first and second back electrode films are formed at a plurality of connection locations in a light-receiving region. A photoelectric conversion element in which a two-electrode film penetrates through the insulating film and is electrically coupled to the light-receiving surface electrode film, wherein q is an elementary charge and k is a Boltzmann constant; Is given by T (absolute temperature), i _ph (photocurrent density), i ₀ (reverse saturation current density), R _s (series resistance) R _sh under given conditions.
(Shunt resistance) and the film thickness determined from the value of R _st (sheet resistance) at which the output power based on the output current calculated by the following equation using the value of n (n value of the diode characteristic) becomes substantially maximum. A photoelectric conversion element, characterized in that: i (r) = i _ph −i ₀ [exp ｛q (V (r) + R _s i (r)) /
nkT} -1] - (V ( r) + R s i (r)) / R sh dV (r) / dr = I (r) · R st / 2πr However, I _out: output current at one connecting point i (r): the amount of current generated in a minute area at a radius r point I (r): the total amount of current flowing in the direction of a contact hole in a ring-shaped area at a radius r point V (r): the voltage at a radius r point R: connection Radius of a circle having the same area as the square corresponding to the arrangement interval of the points _R0 : radius of the connection point 2. The method according to claim 1, wherein the first and second back electrode films of the photoelectric conversion elements adjacent to each other are coupled to the semiconductor film on the back side. A photovoltaic device, wherein the photovoltaic devices are electrically connected in series.