DECOUPLING OF A PEROVSKITE SOLAR CELL IN DARKNESS

Abstract

A method for operating a photovoltaic module in which the photovoltaic module has at least one perovskite solar cell. The method includes temporarily operating the photovoltaic module at the maximum power point by a control device connected to the photovoltaic module, wherein the drawing of electrical energy is interrupted when the irradiance of electromagnetic radiation impinging on the photovoltaic module falls below a predetermined threshold value. A photovoltaic device includes a photovoltaic module having at least one perovskite solar cell, and a control device connected to the photovoltaic module.

Claims

1. A method for operating a photovoltaic module having at least one perovskite solar cell, the method comprising: operating, at least temporarily, the photovoltaic module at a maximum power point by a regulation device connected to the photovoltaic module, wherein a withdrawal of electrical energy is interrupted when an irradiance of an electromagnetic radiation impinging on the photovoltaic module falls below a predetermined threshold value, wherein, when the irradiance falls below the predetermined threshold value, the photovoltaic module is electrically decoupled from the regulation device by a transistor and wherein the predetermined threshold value is in a range of between 2 W/m.sup.2 and 20 W/m.sup.2.

2. The method as claimed in claim 1, wherein the photovoltaic module is operated at the maximum power point by the regulation device substantially throughout a time period in which the irradiance exceeds the predetermined threshold value.

3. The method as claimed in claim 1, wherein, when the irradiance falls below the predetermined threshold value, the photovoltaic module is short-circuited.

4. The method as claimed in claim 1, wherein a photocurrent generated by the photovoltaic module is used as a measure of the irradiance of the electromagnetic radiation impinging on the photovoltaic module.

5. The method as claimed in claim 1, wherein the irradiance of the electromagnetic radiation impinging on the photovoltaic module is determined by impedance spectroscopy at one or more perovskite solar cells of the photovoltaic module.

6. The method as claimed in claim 1, wherein the photovoltaic module has an additional photoelectric cell, and the irradiance of the electromagnetic radiation impinging on the photovoltaic module is determined by means of the additional photoelectric cell.

7. The method as claimed in claim 6, wherein the irradiance is determined by a photocurrent generated by the additional photoelectric cell.

8. The method as claimed in claim 1, wherein the irradiance of the electromagnetic radiation impinging on the photovoltaic module is estimated on the basis of meteorological data.

9. The method as claimed in claim 1, wherein the regulation device is an inverter, or a microinverter, assigned to the photovoltaic module.

10. The method as claimed in claim 1, wherein the regulation device is a power optimizer assigned to the photovoltaic module.

11. A photovoltaic device comprising: a photovoltaic module having at least one perovskite solar cell, and a regulation device connected to the photovoltaic module, wherein the regulation device is configured to operate the photovoltaic module at least temporarily at a maximum power point and to interrupt the an energy withdrawal when an irradiance of an electromagnetic radiation impinging on the photovoltaic module falls below a predetermined threshold value, wherein, when the irradiance falls below the predetermined threshold value, the photovoltaic module is electrically decoupled from the regulation device, and wherein the predetermined threshold value is in a range of between 2 W/m.sup.2 and 20 W/m.sup.2.

12. The method as claimed in claim 1, wherein the predetermined threshold value is in the range of between 5 W/m.sup.2 and 15 W/m.sup.2.

13. The method as claimed in claim 1, wherein the predetermined threshold value is 10 W/m.sup.2.

14. The photovoltaic device as claimed in claim 11, wherein the predetermined threshold value is in the range of between 5 W/m.sup.2 and 15 W/m.sup.2.

15. The photovoltaic device as claimed in claim 11, wherein the predetermined threshold value is 10 W/m.sup.2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The invention will be illustrated below with reference to the attached figures, in which:

[0037] FIG. 1 shows a photovoltaic module, which is electrically decoupled from a regulation device so that the withdrawal of electrical energy is interrupted,

[0038] FIG. 2 shows the same photovoltaic module, which is now electrically connected to the regulation device so that the photovoltaic module can be operated at the maximum power point,

[0039] FIG. 3 shows the same photovoltaic module, which is now short-circuited, and

[0040] FIG. 4 shows the developments of the efficiencies of two perovskite solar cells over time.

DETAILED DESCRIPTION OF THE INVENTION

[0041] FIGS. 1 to 3 (also referred to as FIGS. 1 to 3) show an exemplary embodiment of a photovoltaic device 1 according to the invention. The photovoltaic device 1 has a photovoltaic module 10 having a multiplicity of perovskite solar cells 11, of which only one is shown in FIG. 1 for reasons of clarity. Each of the perovskite solar cells 11 has an electron transport layer, a light-absorbing layer (also referred to as “absorber”) and a hole transport layer. The absorber contains a perovskite having the general structural formula ABX.sub.3, where, for example, A=CH.sub.3NH.sub.3, B=Pb and X=I.sub.3. Furthermore, the solar cell has a front contact 111 and a rear contact 112. The front contact 111 is advantageously transparent to electromagnetic radiation from a specific wavelength range for which the solar cell is designed. The rear contact can be configured to cover the full area and to be non-transparent (for example comprising an aluminum alloy). The perovskite solar cells 11 are embedded in glass sheets which are intended to protect it from, for example, contamination and damage.

[0042] FIGS. 1 to 3 also show electromagnetic radiation 2 of the Sun (also referred to as “solar radiation”) which impinges on the front of the photovoltaic module 10 and therefore also on the front of the perovskite solar cell 11.

[0043] The front and rear contacts 111, 112 of the solar cell 11 shown in FIG. 1 are electrically conductively connectable to a regulation device 20. The photovoltaic module 10 can namely be electrically connected to or electrically decoupled from the regulation device 20 by means of a switch 30. In addition, the photovoltaic module 10 can also be short-circuited by means of the switch 30.

[0044] FIG. 1 shows a sketch of a first position 301 of the switch 30. In the first position 301, the switch is open and the photovoltaic module 10 is electrically disconnected from the regulation device 20. Therefore, an open circuit voltage is present at the photovoltaic module 10. No energy is withdrawn from the photovoltaic module 10.

[0045] FIG. 2 shows a sketch of a second position 302 of the switch 30. In the second position 302, the switch is closed and the electrical connection between the photovoltaic module 10 and the regulation device 20 has been produced. The regulation device 20 is capable of withdrawing the maximum power (or correspondingly the maximum energy) from the photovoltaic module by virtue of matching its load resistance to the currently present internal resistance of the photovoltaic module.

[0046] FIG. 3 shows a sketch of a third position 303 of the switch 30. In the third position 303, the switch connects the front contact 111 and the rear contact 112 of the photovoltaic module 10 and therefore short-circuits the latter. A corresponding short-circuit current flows at the photovoltaic module 10, and it is not possible for any energy to be withdrawn from the photovoltaic module 10 either.

[0047] In particular, the regulation device 20 itself can set the switch 30 into the respectively appropriate position 301, 302, 303. When the irradiance is sufficiently high, the switch is closed (position 302) and maximum power point tracking of the photovoltaic module 10 takes place. However, if the irradiance falls below a predetermined threshold value, the photovoltaic module 10 is either decoupled from the regulation device (position 301) or short-circuited. In both cases, the result is that maximum power point tracking of the photovoltaic module by means of the regulation device 20 is no longer possible, and therefore degradation of the perovskite solar cell(s) 11 of the photovoltaic module 10 is prevented or at least reduced.

[0048] FIG. 4 (also referred to as FIG. 4) shows the characteristic of the efficiency of a first perovskite solar cell 53 over time and the characteristic of the efficiency of a second perovskite solar cell 54 over time. The time in hours is plotted on the x axis 51, and the standardized efficiency is plotted on the y axis 52. The efficiency is plotted in standardized form, i.e., it was set to the relative value of 1.0 for both solar cells at the beginning of the measurements. Both solar cells are comparable in terms of design, material and power. Both solar cells have been artificially illuminated for in each case six hours, in each case interrupted by a six-hour time period in darkness. This should simulate the day/night rhythm, shortened in time. The illumination corresponded in terms of intensity and spectrum to real illumination by sunlight, for example.

[0049] The first solar cell was connected to a conventional regulation device for operating the solar cell at the maximum power point, i.e., a so-called “maximum power point tracking regulation device”, throughout the measurement time period of 100 hours (approximately 8 day/night cycles). In particular, the solar cell was also connected to the mentioned regulation device or “loaded” during the dark periods.

[0050] This resulted in a considerable degradation of the efficiency of the solar cell under investigation. At the end of the 100-hour measurement time period, the efficiency of the solar cell was now only approximately a quarter of the value at the beginning of the investigations.

[0051] The second solar cell was disconnected from the “maximum power point tracking regulation device” during the time periods during which the cell was in darkness (8×6 hours). Here too, firstly a certain degradation of the cell efficiency can be observed during the light phases and secondly a certain degradation of the efficiency can be observed during the dark times. However, the degradation was much less than the first solar cell which was permanently connected to the regulation device. At the end of the 100-hour measurement time period, the efficiency of the solar cell was even so still approximately three-quarters of the value at the beginning of the investigations.

[0052] The disconnection of a photovoltaic module having a perovskite solar cell from the MPPT regulation device during darkness (or weak light) can therefore diminish the degradation of the perovskite solar cell, possibly even completely eliminate it or at least limit it.

LIST OF REFERENCE SYMBOLS

[0053] 1 photovoltaic device [0054] 2 electromagnetic radiation [0055] 10 photovoltaic module [0056] 11 perovskite solar cell [0057] 111 front contact [0058] 112 rear contact [0059] 20 regulation device [0060] 30 switch [0061] 301 first position [0062] 302 second position [0063] 303 third position [0064] 51 x axis [0065] 52 y axis [0066] 53 efficiency of a first perovskite solar cell [0067] 54 efficiency of a second perovskite solar cell