Energy-efficient cooling of perovskite solar cells

Abstract

Energy-efficient cooling of perovskite solar cells. The invention relates to a control of a cooling device for actively cooling a perovskite solar cell, wherein the perovskite solar cell is part of a perovskite photovoltaic module. The method comprises the following steps: - taking a measure of an internal temperature of the perovskite solar cell; and - activating the cooling device when the taken measure of the internal temperature of the perovskite solar cell is greater than a corresponding measure of a predetermined temperature threshold. The invention further relates to a photovoltaic device having a perovskite photovoltaic module with at least one perovskite solar cell and a cooling device for actively cooling the perovskite solar cell.

Description

Technical Field

[0001] This invention relates to a method for controlling the active cooling of a perovskite solar cell. The invention also relates to a photovoltaic device having a perovskite photovoltaic module and a cooling device, the perovskite photovoltaic module having at least one perovskite solar cell, and the cooling device being used for actively cooling the perovskite solar cell. Background Technology

[0002] It is known that the efficiency of perovskite solar cells typically decreases at high temperatures. This decrease or degradation in efficiency at high temperatures is often not only more pronounced than in conventional crystalline silicon solar cells, but may also be irreversible. The following temperature is also known as the critical temperature: above which there is a risk of permanent damage to the perovskite solar cell. Therefore, it is important that the temperature of the perovskite solar cell remains below this critical temperature, even under conditions such as high solar radiation.

[0003] The critical temperature is strongly related to the structure, material composition, and processing of perovskite solar cells. Under certain conditions, the critical temperature of perovskite solar cells can be as low as 50°C or 60°C—temperatures that solar cells typically reach quickly during operation.

[0004] The first approach to addressing the challenge of perovskite solar cells degrading above their critical temperature is to modify their structure, material composition, and / or processing. This modification is undertaken with the objective of raising the level (in other words, increasing) the critical temperature of the perovskite solar cell.

[0005] The second approach involves finding methods and means to at least partially "cure" the efficiency degradation caused by the high temperatures experienced by perovskite solar cells. In other words, this approach aims to at least partially reverse the assumed irreversible damage to the perovskite material.

[0006] To date, neither the first nor the second approach has been able to achieve a completely satisfactory and practical solution. Summary of the Invention

[0007] The purpose of this invention is to develop an alternative design concept to reduce the risk of permanent damage to perovskite solar cells due to thermal effects.

[0008] The objective is achieved by the method for controlling a cooling device and a photovoltaic device according to the present invention. Advantageous improvements and embodiments are disclosed in the specification and drawings.

[0009] The method according to the invention relates to the control of a cooling device for actively cooling perovskite solar cells, wherein the perovskite solar cells are part of a perovskite photovoltaic module. The method includes the following steps:

[0010] - Determine the measurement of the internal temperature of a perovskite solar cell, and

[0011] - When the measured internal temperature of the perovskite solar cell exceeds the measured value corresponding to a predetermined temperature threshold, the cooling device is activated.

[0012] In other words, the perovskite solar cell is cooled when necessary, specifically when the temperature exceeds a certain threshold that is advantageously below the critical temperature of the perovskite solar cell. This prevents the perovskite solar cell from being subjected to temperatures higher than its critical temperature. This avoids potentially irreversible damage to the solar cell from the outset.

[0013] Cooling is controlled based on the internal temperature of the perovskite solar cell or a corresponding measurement of that temperature. Specifically, the internal temperature of the perovskite solar cell is measured continuously or intermittently. If the measurement exceeds a predetermined threshold, the cooling system is activated. If the internal temperature measurement drops below the threshold again, the cooling system is deactivated. This achieves energy-efficient, efficient, and demand-compliant cooling of (multiple) perovskite solar cells.

[0014] An important aspect of this invention is the activation of a cooling device based on the internal temperature of the perovskite solar cell. The internal temperature (also known as "bulk temperature" in English technical terms) should be understood here as distinct from the surface temperature. The internal temperature of a solar cell particularly relates to the temperature of its light-absorbing layer. In the case of a perovskite solar cell with a pin structure, i.e., having a hole-conducting layer, an intrinsic layer, and an electron-conducting layer, the light-absorbing layer particularly includes the intrinsic layer. In a perovskite solar cell, the intrinsic layer, for example, has a (crystalline) structure CH3NH3PbI3. Because the inherent perovskite-based layer in a perovskite solar cell will irreversibly degrade when subjected to temperatures above the critical temperature, the temperature of said region of the solar cell, i.e., its internal temperature, is particularly important. On the other hand, if, for example, the temperature at the front contact of the perovskite solar cell is above the critical temperature, but the actual temperature of the light-absorbing layer is below the critical temperature, then the perovskite solar cell remains in the "green zone" and activation of solar cell cooling is not necessary.

[0015] Another important aspect of the invention is the active cooling of perovskite solar cells according to the method described in the invention. This is particularly considered to be different from permanent cooling. Because the internal temperature of the perovskite solar cell, or its corresponding measurement, is used as a regulating variable for the cooling device, cooling is ensured to operate only when there is also a need for cooling. Therefore, the method according to the invention is energy-efficient, thereby saving money and resources.

[0016] Active cooling has the particular advantage of being energy-efficient because it only cools when needed. Advantageously, active cooling has relatively high cooling power so as to also safely prevent the internal temperature from exceeding the critical temperature of the solar cell with the highest possible probability. That is, the method according to the invention provides a reliable and energy-efficient cooling mechanism for perovskite solar cells that reduces the risk of persistent damage to perovskite solar cells due to thermal effects.

[0017] Active cooling is also considered different from so-called back ventilation. Back ventilation of photovoltaic modules is known from photovoltaic modules with conventional crystalline silicon solar cells. For this purpose, the photovoltaic modules are installed at a certain distance from the roof. To achieve adequate back ventilation of the photovoltaic modules, it is recommended to maintain a distance of approximately 10 cm between the roof and the modules. Back ventilation of the modules works through convection of air. A chimney effect is generated in the space between the photovoltaic modules and the roof cladding, and the intensity of this effect (and thus cooling) is related not only to the size of the distance between the roof and the modules, but also to the material of the roof cladding and the underside of the modules. Height-adjustable roof hooks exist, which make it easier to adhere to the desired distance.

[0018] Clearly, perovskite photovoltaic modules typically have more than one perovskite solar cell, i.e., multiple perovskite solar cells. Perovskite solar cells can also be part of a series cell constructed from a perovskite solar cell and another solar cell, such as a conventional silicon solar cell. For such series solar cells, an impressive efficiency of 28% has recently been achieved in laboratory standards.

[0019] The first method step includes measuring the internal temperature of the perovskite solar cell. If the perovskite photovoltaic module has multiple perovskite solar cells, then the first method step can also include measuring the internal temperature of the multiple perovskite solar cells of the perovskite photovoltaic module.

[0020] The measurement of internal temperature can be understood as any parameter suitable for characterizing the internal temperature of a perovskite solar cell. This can be a real temperature directly in Kelvin (or Celsius or Fahrenheit). However, it can also be a current intensity in amperes or a voltage in volts, which cannot be directly converted into a specific temperature, but can still be used to estimate whether the current internal temperature of the perovskite solar cell is above or below a predetermined temperature threshold.

[0021] The predetermined temperature threshold is advantageously selected such that it is slightly below the critical temperature. Depending on the design of the cooling device, particularly in terms of cooling power, the temperature threshold should be selected such that, after exceeding the temperature threshold and activating the cooling device, the temperature typically only rises further to such that the temperature is always kept below the critical temperature of the perovskite solar cell.

[0022] The "predetermined" temperature threshold should be understood as a preset temperature threshold. Given that the critical temperature of perovskite solar cells is strongly correlated with the specific cell type, the corresponding temperature threshold should be determined individually, from which the perovskite solar cell faces irreversible efficiency degradation.

[0023] Different methods can be considered to specifically determine the internal temperature or a measure of the internal temperature.

[0024] The first method is based on impedance spectroscopy, particularly electrochemical impedance spectroscopy. To do this, an alternating voltage is applied to the perovskite solar cell, and the resulting current flow is measured at different frequencies of the alternating voltage. Based on a suitable depiction of the measurement results, for example in the form of a so-called Bode plot or Nyquist plot, conclusions can then be drawn about the internal parameters of the perovskite solar cell, such as carrier transport or recombination rate. In particular, the internal temperature of the perovskite solar cell can also be determined using impedance spectroscopy, as described in, for example, international patent application PCT / EP2019 / 074317 filed on September 12, 2019.

[0025] A second method for determining the internal temperature of a perovskite solar cell involves using a thermocouple. A thermocouple consists of a pair of metal conductors made of different materials, connected at one end and suitable for temperature measurement due to the thermoelectric effect. In principle, the thermocouple provides electrical energy from heat when there is a temperature difference along the conductors. The voltage appearing at the ends of the metal conductors is relatively small and ranges from tens of μV per 1°C temperature difference. The two metal conductors of the thermocouple are advantageously directly connected to the light-absorbing layer of the perovskite solar cell, i.e., its intrinsic layer, for example. This connection is typically permanent, allowing continuous monitoring of the internal temperature of the solar cell during operation of the perovskite photovoltaic module.

[0026] Different implementation schemes can be considered for the specific design of cooling equipment used for actively cooling perovskite solar cells.

[0027] For example, it is feasible to cool solar cells using a cooling liquid. The cooling liquid can be guided in a pipe or hose near the solar cell. The cooling device in this case meaningfully has an inlet and an outlet, where the temperature of the cooling liquid in the inlet is below a predetermined temperature threshold, at which cooling is activated. The cooling liquid can be substantially composed of water, with optional additives added to the water to lower the freezing point and / or raise the boiling point.

[0028] Liquid-based cooling of perovskite solar cells, for example by means of rainwater, is also feasible. The rainwater is collected and controlledly guided onto the tilted surface of the perovskite photovoltaic module. In this case, when a predetermined temperature threshold is exceeded, rainwater is guided onto the module surface, where the water temperature is lower than the photovoltaic module temperature, thereby causing cooling of the module and the perovskite solar cells contained therein. Cooling is controlled based on the internal temperature of the perovskite solar cell or a corresponding measurement of the internal temperature. That is, the measurement of the internal temperature of the perovskite solar cell is taken continuously or intermittently. If the measurement exceeds the predetermined threshold, then the cooling device is activated by means of a rainwater reservoir, for example by opening a valve at the reservoir's outlet. Using rainwater is advantageous in that it can thereby avoid possible calcium-containing residues on the module surface. However, alternative cooling liquids can, of course, be considered in principle. Furthermore, the use of rainwater in an open system, where the rainwater can evaporate and utilize the heat of evaporation (also known as "latent heat of vaporization"), is also considered. () to cool the (multiple) perovskite solar cells of the photovoltaic module.

[0029] In another embodiment of the invention, the cooling device has a radiator for outputting heat via thermal radiation. The radiator is, for example, made of a metal with good thermal conductivity and has a surface with high emissivity.

[0030] Radiators (and other designs for cooling devices) are particularly positioned on the side of the perovskite photovoltaic module facing away from the sun. This has the advantage that the design causes absolutely no shading of the solar cells. Furthermore, it minimizes the heating of the cooling devices.

[0031] In another embodiment of the invention, the cooling device has a Peltier element. When the cooling device is activated, the current flowing through the Peltier element causes a decrease in the internal temperature of the perovskite solar cell.

[0032] Here, a Peltier element is understood as an electrothermal converter that generates a temperature difference based on the Peltier effect when current flows through it. Therefore, a Peltier element can be used to cool objects thermally connected to it. In this application, the Peltier element is also referred to as a Peltier cooler or TEC (thermoeletric cooler).

[0033] In another embodiment of the invention, the cooling device has multiple channels in the cover plate of the perovskite photovoltaic module. The cover plate is, for example, a glass sheet, particularly a monolithic safety glass. The channels have a small size compared to the rest of the photovoltaic module and are technically referred to as microchannels. When the cooling device is activated, a cooling liquid flows through the channels. Compared to the component to be cooled, i.e., the perovskite solar cell, the cooling liquid again has a lower temperature. Therefore, the cooling liquid absorbs a portion of the heat energy of the perovskite solar cell, thereby ensuring the cooling of the internal temperature of the perovskite solar cell.

[0034] When the cooling device is located, for example, outside the perovskite photovoltaic module, there is an advantage to good thermal conduction from the cooling medium to the perovskite solar cell to be cooled.

[0035] In addition to the method for controlling a cooling device according to the invention described herein, the invention also relates to a photovoltaic device having a perovskite photovoltaic module and a cooling device. The perovskite photovoltaic module has one or more perovskite solar cells. The cooling device is adapted to actively cool the perovskite solar cells. The photovoltaic device also has a control device for controlling the cooling device. The control device is particularly designed for implementing the method according to one of the above embodiments.

[0036] Active cooling of perovskite photovoltaic modules can also be optionally combined with passive cooling mechanisms of the module or with passive temperature stabilization mechanisms of the perovskite photovoltaic module. Known passive temperature stabilization mechanisms for this purpose provide a large thermal mass, for example, in the form of a water tank on the back side of the photovoltaic module, or use a latent heat storage device that stores most of the thermal energy delivered to it in the form of latent heat (e.g., for a phase change from solid to liquid).

Claims

1. A method for controlling a cooling apparatus for active cooling of a perovskite solar cell, wherein the perovskite solar cell is part of a perovskite photovoltaic module, the method comprising the following steps: - Determine the measurement of the internal temperature of the perovskite solar cell, and - When the calculated internal temperature of the perovskite solar cell exceeds a predetermined temperature threshold, the cooling device is activated. The perovskite solar cell has a light-absorbing layer and the measure of the internal temperature is the actual temperature of the light-absorbing layer of the perovskite solar cell.

2. The method according to claim 1, The internal temperature of the perovskite solar cell is determined by means of impedance spectroscopy.

3. The method according to claim 1, The internal temperature of the perovskite solar cell is measured using a thermocouple.

4. The method according to any one of claims 1 to 3, The cooling device is located on the side of the perovskite photovoltaic module that is away from the sun.

5. The method according to any one of claims 1 to 3, The cooling device includes a Peltier element, and when the cooling device is activated, the current flowing through the Peltier element causes a decrease in the internal temperature of the perovskite solar cell.

6. The method according to any one of claims 1 to 3, The cooling device includes a cooling liquid that has a temperature lower than the temperature threshold at least when the cooling device is activated, in the inlet portion of the cooling device.

7. The method according to any one of claims 1 to 3, The cooling device described therein has a radiator for outputting heat through thermal radiation.

8. The method according to any one of claims 1 to 3, The cooling device described therein has multiple channels in the cover plate of the perovskite photovoltaic module.

9. The method according to claim 8, When the cooling device is activated, the cooling liquid flows through the channel and absorbs a portion of the thermal energy of the perovskite solar cell.

10. The method according to any one of claims 1 to 3, The perovskite photovoltaic module has a frame, and the perovskite solar cell is thermally connected to the frame.

11. A photovoltaic device, the photovoltaic device comprising: A perovskite photovoltaic module, wherein the perovskite photovoltaic module has at least one perovskite solar cell; A cooling device for actively cooling the perovskite solar cell, wherein the photovoltaic device further comprises a control device for controlling the cooling device, wherein the control device is designed to perform the method according to any one of claims 1 to 10.