JPH0795091B2 - Solar cell evaluation method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating a solar cell by obtaining a dispersion distribution of a light receiving surface with respect to a photo-generated current and a series resistance which are equivalent circuit parameters of the measured solar cell.

[0002]

2. Description of the Related Art Conventionally, the following method has been known as a technique for estimating an equivalent circuit parameter of this kind [Yui, Hayashi: Transactions of the Institute of Electrical Engineers of Japan, B, 112, 9, 835 (1992). ]. That is, bias light (light similar to the spectral distribution of sunlight)
Direct current during operation by irradiating the entire surface of the measured solar cell
The DC voltage characteristic can be expressed by the following equation (1) using the typical equivalent circuit shown in FIG.

[0003]

[Formula 2]

Where I _p : photogenerated current, I, V: DC output current and DC output voltage, R _s, R _sh : series resistance and parallel resistance,
I _s : diode saturation current, n: diode ideality factor, q: electron charge, K: Boltzmann constant, T: temperature
(k).

When an extremely weak white light Δφ _m [W] having the same spectral distribution as the bias light and an intensity that can be ignored is superimposed on this state, the weak output current Δi [A] has a constant DC output voltage, Assuming that the change in equivalent circuit parameter can be ignored, it is given by the difference in DC output current with and without weak white light irradiation. Therefore, letting the weak white light generation current be Δi _p [A], the following (2 ) Can be expressed as

[0006]

[Formula 3]

Here, if a part of {} is replaced by the A factor shown in the following equation (3), the above equation (2) becomes the following equation (4).

[0008]

[Formula 4]

[0009]

[Formula 5]

On the other hand, the following formula (5) is obtained by differentiating the formula (1) by the DC voltage V and using the formula (3). Therefore, the formula (4) can be arranged by the formula (6) below. .

[0011]

[Formula 6]

[0012]

[Formula 7]

Since the weak output current Δi based on the irradiation of the weak white light is associated with the DC current-DC voltage characteristic in this manner, the weak white light generation current Δi _p at the operating point The resistance R _s can be calculated by the following method.

Here, Δi and dI near the operating point
/ dV is given as the measured quantity, and Δi,
And R _s can be assumed to show a constant value, then Δ i and
Since there can be two or more sets of the above equation (6) with dI / dV as a variable, the values of the weak white light generation current Δi _p and the series resistance R _{s at} the operating point can be calculated by solving them.

Here, if the intensity ratio of the bias light and the weak white light is, for example, 1: 100, 100 times the weak white light generation current Δi _p is the magnitude of the light generation current due to the irradiation of the bias light. is there.

Therefore, in this method, the values of the bias light generation current I _p , the weak white light generation current Δi _p and the series resistance R _s of the measured solar cell at the operating point can be determined.

[0017]

However, the evaluation of the faint white light generation current Δi _p and the series resistance R _s by the above conventional method is performed when the model of the equivalent circuit shown in FIG. 4 is satisfied, that is, the light generation current Δi _p. And the series resistance R _s , the A factor that determines the A factor, the n value, the saturation current value I _s , the parallel resistance R _sh, etc. show a constant value in any part of the light receiving surface. However, it was limited to solar cells made of high-quality single crystal silicon having excellent uniformity.

On the other hand, the minority carrier lifetime and the pn junction depth are not uniform depending on the location in the light receiving surface of the solar cell made of polycrystalline silicon in which a large number of crystal grain boundaries, crystal defects and the like are mixed. It is considered that the magnitude of the photogenerated current Δi _p, the n value, the saturation current I _s , the parallel resistance R _sh , the series resistance R _s, etc. show spatially non-uniform values, and the model of the above equivalent circuit collapses. Even if the analysis of the above equation (6) is applied to, weak white light generation current Δi _p , series resistance R _s, etc. are only inaccurate values, and the scope is narrow because of lack of rigor and objectivity. There was a flaw.

[0019]

In order to solve the above-mentioned problems, according to the present invention, a DC bias light and an AC weak white light whose optical axis, beam diameter, and spectral distribution coincide with each other are provided in a specific portion of a light receiving surface of a measured solar cell. And the direct current-DC voltage (IV) characteristic and AC weak white light current-DC voltage (Δi
-V) Measure the characteristics,

[0020]

[Formula 7]

An operation for obtaining the values of the faint white light generation current Δi _P and the series resistance R _S for the specific portion by applying the analytical expression represented by is performed on the entire light receiving surface of the measured solar cell,
The value obtained from this is statistically processed to obtain a weak white light generation current Δi _P and a series resistance R _{S in} the light receiving surface of the measured solar cell.
It proposes an evaluation method for a solar cell which is designed to obtain the dispersion distribution of.

In the present invention, for example, as shown in FIG. 1, for example, a DC bias light (air mass 1.5, 100 mW / cm ² ) 1 and an AC weak white light (air mass 1.5, air beam 2, beam diameter 3, spectral distribution coincident with each other) (air mass 1.5 , 1mW / cm ² or less) 4 is a half mirror 5
Optical system for selectively irradiating the specific portion 8 of the light receiving surface of the measured solar cell 7 mounted on the stage 6 and the direct current-direct current voltage characteristic 11 and the alternating current in the specific portion 8 of the measured solar cell 7 A measurement system provided with an electronic measuring instrument 9 capable of measuring the weak white light current-DC voltage characteristic 12 and a computer 10 for data processing can be used.

Here, the computer 10 fetches and stores new data of the DC current-DC voltage characteristic 11 and the AC weak white light current-DC voltage characteristic 12 each time the position of the stage 6 is moved, and the equation (6) is stored. The analytical expression shown in is applied and used to calculate the AC weak white light generation current Δi _p and series resistance R _s .

[0024]

According to the present invention, the irradiation of the bias light 1 and the AC weak white light 4 generates the DC light generation current and the AC weak white light generation current in the measured solar cell 7 and the specific portion 8.
A part of these photo-generated currents also flows to the part without light irradiation, and the distribution result appears in the data of DC current-DC voltage characteristic 11 and AC weak white light current-DC voltage characteristic 12.

That is, the source of the photo-generated current is limited to the specific portion 8, but since the electric load thereof extends over the entire area of the measured solar cell 7 including the specific portion 8, the direct current-direct current voltage characteristic 11 And the AC weak white light current-DC voltage characteristic 12 have common values for the A factor, AC weak white light generation current Δi _p , and series resistance R _s .

Therefore, the above equation (6) can be applied, and the AC weak white light generation current Δi _p associated with the specific portion 8 is obtained.
And the exact value of the series resistance R _s is known.

Therefore, this process is applied to all the light-receiving surfaces of the measured solar cell 7 to find the AC weak white light generation current Δi _p and the series resistance R _s corresponding to the respective parts,
By subjecting these values to statistical processing such as a histogram, a dispersion distribution 13 of the AC weak white light generation current Δi _{p and} a dispersion distribution of the series resistance R _{s on} the light receiving surface of the measured solar cell 7 are obtained.
14 is obtained, which enables quantitative and objective evaluation of the measured solar cell 7.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in more detail with reference to the embodiment shown in FIG.
The light from 20 is split by a half mirror 22 via a filter 21 of air mass 1.5, and one of them is passed through an aperture 23 and a half mirror 5 to be a DC white light 1 (100 mW / cm ² ).

The other one is made into AC weak white light 4 (1 mW / cm ² ) through the dimmer 24, mirror 25, mechanical chopper 26, aperture 27, mirror 28 and half mirror 5.

For both lights, the beam diameter is 3 (for example, several tens μ
m), irradiating an arbitrary measurement site 8 of the measured solar cell 7 fixed on the movable stage 6 with the optical axis 2 aligned.

Under such light irradiation, the measured solar cell 7
The AC weak white current-DC voltage characteristic 12 having a spectrum substantially equal to the DC current-DC voltage characteristic 11 is obtained at the measurement site 8 of 1., but the measurement system is as follows.

That is, a DC voltage generated by the programmable power supply 30 is converted into a current-voltage conversion circuit having an infinite input impedance.
After converting the AC and DC short-circuit currents of the solar cell 7 to be measured to an AC and DC voltage of appropriate magnitude via 31, a lock-in amplifier 32 for measuring AC weak white generated current signal and DC current signal measurement The computer 10 is used for automatic measurement and data processing.

In the above measurement system, the programmable power supply 30
After setting the increase rate of the DC voltage with, lock-in amplifier 32
The program of the computer 10 is built to repeat the cycle of reading and storing the indicated value of the DC voltmeter 33 until the open voltage is reached, which allows the DC current-DC voltage characteristic 11 and the AC weak white light current-DC voltage. The characteristic 12 is obtained, and from this, the weak white light generation current Δi _p and the series resistance R _s at the operating point are obtained by applying the above equation (6).

Further, by operating the movable stage 6, a weak white light generation current Δi _p and a series resistance R _s at another measurement site 8 of the measured solar cell 7 are obtained, and a histogram of Δi _p is obtained based on the data thus obtained. 13 and the histogram 14 of R _s can be created to know the dispersion distribution on each light receiving surface.

[0035]

In summary, according to the present invention, the dispersion distribution of the weak white light generation current Δi _p and the series resistance R _s in the light receiving surface of the measured solar cell, which has been impossible in the past, can be known, and The quality of the measured solar cell can be accurately evaluated.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of the present invention.

FIG. 2 is a measurement system diagram showing an embodiment of the present invention.

[Fig. 3] Statistical processing diagram obtained by the above measurement system

FIG. 4 Equivalent circuit of solar cell

[Explanation of symbols]

1 DC bias light 2 Optical axis 3 Beam diameter 4 AC weak white light 5 Half mirror 6 Stage 7 Solar cell to be measured 8 Measurement site 9 Electronic measuring instrument 10 Computer 11 DC current-DC voltage characteristic 12 AC weak white light current-DC voltage Characteristic 13 Dispersion distribution curve of AC weak white light generation current Δi _p of measured solar cell 14 Dispersion distribution curve of series resistance R _s of measured solar cell 20 Xenon lamp with DC lighting 21 Filter 22 Half mirror 23 Aperture 24 Dimmer 25 Mirror 26 Mechanical chopper 27 Aperture 28 Mirror 30 Programmable power supply 31 Current-voltage conversion circuit 32 Lock-in amplifier 33 DC voltmeter

Claims (1)

[Claims] 1. A direct current-direct current voltage (I)
-V) characteristics and AC weak white light current-DC voltage (Δi-
V) Measure the characteristics, The operation of obtaining the values of the faint white light generation current Δi _p and the series resistance R _s for the specific portion by applying the analytical formula expressed by is performed on the entire light receiving surface of the measured solar cell, and the value obtained from this is calculated. A method of evaluating a solar cell, characterized in that a statistical distribution is obtained to obtain a dispersion distribution of a weak white light generation current Δi _p and a series resistance R _{s in} the light receiving surface of the measured solar cell.