Patent Description:
The present application particularly relates to a measurement method of the subcell photocurrents and their matching degree of a multi-junction photovoltaic cell, belonging to the technical field of semiconductor testing. The document <CIT> is a relevant prior art.

Multi-junction lamination is an effective manner to boost the voltage of a solar cell or a laser photovoltaic cell. The outstanding performance of the multi-junction photovoltaic cell in the aspect of conversion efficiency have drawn attentions from researchers. The photocurrent of the multi-junction cell is mainly determined by the smallest subcell photocurrent. If it is desired to obtain a cell having high conversion efficiency, it is ensured that the photocurrents of all subcells are equal, namely current matched. Under the requirement that the photocurrents are matched, the thicknesses of subcells are determined by the light fluxes absorbed by the material. However, the structure of the manufactured photovoltaic cell difficultly ensures that the photocurrents of subcells are precisely matched, and therefore inspecting whether the subcell photocurrents of the manufactured multi-junction photovoltaic cell are matched is extremely important in terms of testing and analyzing the multi-junction photovoltaic cell.

In the prior art, whether the subcell photocurrents of the photovoltaic cell are mainly matched is judged by measuring the External Quantum Efficiencies (EQEs) or Spectrum Responses (SRs) of the cell; however, for a multi-junction solar cell, it is needed to apply bias laser so that the photocurrent of the subcell not being tested is in a super-saturation state, and the effect of the subcell not being tested on the subcell being tested is eliminated. If it is desired to obtain the subcell photocurrents of a multi-junction solar cell, it is necessary to successively apply different bias lasers based on the number of subcells to measure the SRs and then calculate the short-circuit currents of subcells in combination with standard spectrum integral. The process of measuring the current matching degree of the multi-junction solar cell is relatively complicated and time-consuming. For the multi-junction laser photovoltaic cell, by comparing the deviation between the wavelength at the maximum SR value and the target wavelength, whether the cell reaches the maximum efficiency at a target wavelength is judged, but the subcell photocurrents of the multi-junction laser photovoltaic cell at a certain wavelength cannot be quantitatively determined. Since the subcells in the multi-junction laser photovoltaic cell are made of the same material, information on the current matching degree of subcells cannot be acquired by using a method that bias light is applied to measure the SR. Moreover, there are currently no good methods for inspecting the current matching degree of the multi-junction laser photovoltaic cell at a certain wavelength.

The main objective of the present application is to provide a measurement method of subcell photocurrents and their matching degree of a multi-junction photovoltaic cell in order to overcome the defects in the prior art.

In order to achieve the objective of the disclosure, the technical solution adopted by the present application is as follows:.

An embodiment of the present application provides a measurement method of subcell photocurrents as recited in claim <NUM>. Further advantageous embodiments are recited in the dependent claims.

In view of the defects in the prior art, the inventors of this case have performed long-term researches and lots of practices to propose the technical solution of the present application. Next, the technical solution, its implementation process and principle will be further explained and described.

The measurement method of the subcell photocurrents and their matching degree of the multi-junction photovoltaic cell provided by the present application can provide the approximate values of the subcell photocurrents (the short-circuit current is a current when the voltage is <NUM> V, ideally, it is generally believed that the short-circuit current of a subcell is equal to the photocurrent of the subcell) ; for the multi-junction laser photovoltaic cell, the reverse breakdown voltages of subcells are determined by their doping concentrations as the bandgap of the subcell is consistent; if the doping concentrations at the light doping side of the PN junction of subcells are different, the short-circuit current of the subcell having a lower doping concentration corresponds to the current of a wider step in the curve, and the short-circuit current of the subcell having a higher doping concentration corresponds to the current of a narrower step in the curve; if the dopings of subcells are the same, the corresponding relationship between the subcells and the current steps in the I-V curve cannot be clarified, but one group of subcell short-circuit current values can also be quantitatively obtained. For the multi-junction solar cell or the multi-junction laser photovoltaic cell, the present application can give the matching degree of the subcell photocurrents through measuring the subcell photocurrents instead of analyzing the current match of subcells through indirect means such as External Quantum Efficiency (EQE).

The present application discloses a measurement method of the subcell photocurrents and their matching degree of a multi-junction photovoltaic cell. The detection tool adopted in the measurement method includes a high-precise source meter, a power-stable light source (a solar simulator for the multi-junction solar cell, and a power-tunable laser for the laser photovoltaic cell) and a photovoltaic cell I-V test system. The measurement method comprises the steps of connecting the multi-junction photovoltaic cell with the high-precise source meter using the four-wire method, irradiating the multi-junction photovoltaic cell using the light source, measuring the I-V curve from the reverse bias voltage to the forward bias voltage or from the forward bias voltage to the reverse bias voltage, measuring current values corresponding to all the steps occurring in the I-V curve, and calculating the current mismatching degree of the multi-junction photovoltaic cell.

An embodiment of the present application provides a measurement method of the subcell photocurrents and their matching degree of a multi-junction photovoltaic cell, comprising:.

Further, the measurement method comprises: irradiating the multi-junction photovoltaic cell using a light source having stable output power and meanwhile scanning the multi-junction photovoltaic cell within a set voltage scanning range to obtain the I-V curve.

Further, the set voltage scanning range is from a reverse bias voltage to a forward bias voltage.

Further, the set voltage scanning range is from a reverse breakdown voltage to a forward open-circuit voltage of the photovoltaic cell.

Further, the set voltage scanning range can also be from the forward bias voltage to the reverse bias voltage.

Further, the set voltage scanning range can also be from the forward open-circuit voltage to the reverse breakdown voltage of the photovoltaic cell.

Further, the measurement method specifically comprises:.

Further, the multi-junction photovoltaic cell can be an N-junction laser photovoltaic cell, an N-junction solar cell or an N-junction thermal photovoltaic cell, where N≥<NUM>.

Further, the multi-junction photovoltaic cell is a laser photovoltaic cell whose light source is a laser having stable output power.

Further, the multi-junction photovoltaic cell is a multi-junction solar cell whose light source is a steady solar simulator.

Further, the wavelength of the incident light can be the same as or different from the target wavelength of the multi-junction photovoltaic cell.

Next, the technical solution, its implementation process and principle will be further described in detail in conjunction with the accompanying figures.

As shown in <FIG>, a detection system of the current matching degree of a multi-junction photovoltaic cell is assembled, comprising: a light source <NUM>/<NUM>, a high-precise digital source meter <NUM> and a computer <NUM>, wherein the light source <NUM>/<NUM> is at least used for irradiating the multi-junction photovoltaic cell <NUM>, the high-precise digital source meter <NUM> is connected with the multi-junction photovoltaic cell <NUM> to be detected and at least used for measuring and collecting I-V data obtained when the detected multi-junction photovoltaic cell is irradiated by the light source <NUM>/<NUM>; the computer <NUM> is respectively connected with the light source <NUM>/<NUM> and the high-precise digital source meter <NUM> and at least used for drawing an I-V curve using the I-V data.

Specifically, the high-precise digital source meter <NUM> is the electronic load of the multi-junction photovoltaic cell, the high-precise digital source meter <NUM> is connected with the positive and negative electrodes of the multi-junction photovoltaic cell <NUM> to be detected through the four-wire method which is used to eliminate the voltage test error caused by the series resistances of leads, and the voltage scanning range of the high-precise digital source meter <NUM> is larger than the voltage scanning range required for testing; the computer <NUM> is used for controlling the light source and the digital source meter, mainly including sending a voltage scanning instruction to the high-precise digital source meter, sending turning on/off instructions to the light source and collecting the I-V data tested by the high-precise digital source meter, and drawing an I-V curve using the I-V data.

Specifically, the multi-junction photovoltaic cell to be detected can be a multi-junction laser photovoltaic cell or a multi-junction solar cell. When the multi-junction photovoltaic cell <NUM> to be detected is the multi-junction laser photovoltaic cell, the light source is a power-tunable laser <NUM> whose power is stable. When the multi-junction laser photovoltaic cell is tested, the head of the output optical fiber <NUM> should not be too close to the surface of the multi-junction laser photovoltaic cell to avoid the current-limitation of the tunnel junction; when the multi-junction photovoltaic cell <NUM> to be detected is the multi-junction solar cell, the steady solar simulator is used as the light source.

Specifically, the computer <NUM> and the high-precise digital source meter <NUM> as well as the computer <NUM> and the light source <NUM> are connected through the serial communication data cable <NUM>, and the high-precise digital source meter <NUM> is connected with the positive and negative electrodes of the multi-junction photovoltaic cell <NUM> through wires <NUM>.

Specifically, a measurement method of subcell photocurrents and their matching degree of a multi-junction photovoltaic cell mainly comprises the following steps:.

Specifically, for the multi-junction laser photovoltaic cell, the corresponding relationship between the short-circuit current of each subcell and each step in the I-V curve is determined by the breakdown voltage of the subcell which is affected by the doping concentration at the low doping side in the PN junction; if the doping concentration at the low doping side of the PN-junction is different, the wider step current corresponds to the short-circuit current of the subcell having a lower doping concentration, and the narrower step current corresponds to the short-circuit current of the subcell having a higher doping concentration.

Specifically, the wavelength of the incident light can be the same as or different from the target wavelength of the multi-junction photovoltaic cell, that is, for the multi-junction laser photovoltaic cell, the wavelength of the incident laser can be a wavelength other than the target wavelength and the current matching degree obtained by the measurement method is aimed at the present wavelength used.

It is noted that the measurement method provided by the embodiment of the present application is mainly directed for the matching degree at the target wavelength of the multi-junction photovoltaic cell, however, the measurement method provided by the embodiment of the present application is also applicable to a wavelength (namely non-target wavelength) other than the target wavelength of the multi-junction photovoltaic cell. This is because in the actual manufacturing process of the cell device, there is deflection between the parameters of the used material and the designed ones, leading to a fact that the optimal response wavelength of the finally manufactured cell device deviates from the target wavelength, at this moment, the subcell photocurrents of the multi-junction photovoltaic cell under the target wavelength are not matched.

Specifically, with a multi-junction GaAs laser photovoltaic cell as an example, the ideal multi-junction GaAs laser photovoltaic cell only has the optimal response to a laser having a single wavelength (target wavelength). For example, the multi-junction GaAs laser photovoltaic cell has the maximum short-circuit current under the irradiation of <NUM> laser, and has the diminished short-circuit current under the irradiation of <NUM> laser. However, the actually manufactured laser photovoltaic cell unnecessarily has the optimal response under the <NUM>.

Specifically, the detection process should be performed in a dark chamber in order to reduce the interference of environmental light. Moreover, the temperature of the environment should be recorded since the current matching degree of the subcells is related to the temperature. The bandgap of the material will narrow at higher temperature, which leads to the increase of the absorption coefficient of the material, hence the change of the current matching degree.

In all, at any temperatures and wavelengths, the subcell photocurrents and their matching degree of the multi-junction photovoltaic cell can be obtained by the measurement method provided by the embodiment of the present application.

The measurement method of the subcell photocurrents and their matching degree of the multi-junction photovoltaic cell will be described by using a six-junction <NUM> InGaAs laser photovoltaic cell as an example. A measurement method of the subcell photocurrents and their matching degree of a multi-junction photovoltaic cell comprises the following steps:.

Based on the principle that the higher the doping concentration at the light doping side of the subcell PN junction is, the smaller the width of the current step is, the corresponding relationships between the steps occurring in the I-V curve and the subcells are obtained.

It is noted that the above example is only a preferred application example of the present application, and the protective scope of the present application is not limited. The method for detecting the current matching degree of the subcells utilizing the I-V characteristics provided by the present application can be applied to not only the multi-junction laser photovoltaic cell but also the multi-junction solar cell.

According to the measurement method provided by the embodiment of the present application, the current mismatching degree of the multi-junction photovoltaic cell are obtained by measuring the I-V curve from the reverse bias voltage to the forward bias voltage or from the forward bias voltage to the reverse bias voltage and calculating the mismatching degree using all the step currents occurring in the I-V curve.

Claim 1:
A measurement method of subcell photocurrents and a matching degree of the subcell photocurrents of a multi-junction photovoltaic cell, comprising:
measuring an I-V characteristic of the multi-junction photovoltaic cell (<NUM>) to obtain an I-V curve of the multi-junction photovoltaic cell (<NUM>); and
measuring currents corresponding to respective current steps in the I-V curve to obtain approximate values of short-circuit currents of subcells in the multi-junction photovoltaic cell (<NUM>), and then calculating a mismatching degree of the currents to obtain a current mismatching degree of the multi-junction photovoltaic cell (<NUM>),
wherein to obtain the I-V curve the method comprises irradiating the multi-junction photovoltaic cell (<NUM>) using a light source (<NUM>) having a stable output power and meanwhile scanning the multi-junction photovoltaic cell (<NUM>) within a set voltage scanning range,
wherein
the set voltage scanning range is from a reverse bias voltage to a forward bias voltage, specifically from a reverse breakdown voltage to a forward open-circuit voltage of the multi-junction photovoltaic cell (<NUM>), or
the set voltage scanning range is from a forward bias voltage to a reverse bias voltage, specifically from a forward open-circuit voltage to a reverse breakdown voltage of the multi-junction photovoltaic cell (<NUM>);
characterized in that
the method further comprises
connecting positive and negative electrodes of the multi-junction photovoltaic cell (<NUM>) with a high-precise source meter (<NUM>) using a four-wire method;
placing the multi-junction photovoltaic cell (<NUM>) within a coverage of a light spot; and
setting and turning on the light source (<NUM>) and meanwhile scanning the multi-junction photovoltaic cell (<NUM>) from the reverse bias voltage to the forward bias voltage or from the forward bias voltage to the reverse bias voltage to obtain the I-V curve.