Periodic Reporting for period 5 - CapTherPV (Integration of Capacitor, Thermoelectric and PhotoVoltaic thin films for efficient energy conversion and storage )
Berichtszeitraum: 2021-10-01 bis 2022-07-31
In this project the feasibility of producing a unique device that integrates thermoelectric energy conversion, photovoltaic energy conversion and energy storage was demonstrated.
To achieve this, a thermoelectric device based on transparent materials (thin film oxides) was developed, which, through appropriate engineering, allowed the NIR wavelengths of the solar spectrum to be converted into electrical energy. This combined with a transparent capacitor allowed its integration on top of a solar cell. In this way it was possible to capture the wavelengths not captured by the cells and add a voltage on the order of 0.5 V to the solar cells. This voltage is present even without light. In addition, another capacitor on the back of the solar cells made it possible to store energy that can be supplied during the night or without direct sunlight. This will allow solar cells and photovoltaic panels to have greater flexibility in terms of providing energy in an autonomous manner at low cost.
The demonstration that it is possible to integrate photovoltaic power production and storage in a single device is of great importance, as photovoltaic electricity production combined with energy storage will mitigate the seasonal and daytime limitation of photovoltaic power supply. Furthermore, all the technologies developed are based on environmentally friendly materials, chemicals and techniques, which together with the low cost of the manufacturing process used, the abundance of materials and their easy recyclability enable widespread use and a circular economy.
To achieve this, a thermoelectric device based on transparent materials (thin film oxides) was developed, which, through appropriate engineering, allowed the NIR wavelengths of the solar spectrum to be converted into electrical energy. This combined with a transparent capacitor allowed its integration on top of a solar cell. In this way it was possible to capture the wavelengths not captured by the cells and add a voltage on the order of 0.5 V to the solar cells. This voltage is present even without light. In addition, another capacitor on the back of the solar cells made it possible to store energy that can be supplied during the night or without direct sunlight. This will allow solar cells and photovoltaic panels to have greater flexibility in terms of providing energy in an autonomous manner at low cost.
The demonstration that it is possible to integrate photovoltaic power production and storage in a single device is of great importance, as photovoltaic electricity production combined with energy storage will mitigate the seasonal and daytime limitation of photovoltaic power supply. Furthermore, all the technologies developed are based on environmentally friendly materials, chemicals and techniques, which together with the low cost of the manufacturing process used, the abundance of materials and their easy recyclability enable widespread use and a circular economy.
Several tests were performed to define the best combination of the elements considered in the CapTherPV device. The devices with the best characteristics were placed in a south facing window and the open circuit voltage values were monitored over 18 months (until the end of the project) during day and night. For this period the CapTherPV device provided 0.6V at night and 1.1V during the day (corresponding to the value of the solar cell which depends on the intensity of the solar radiation) with almost no capacitor degradation. Since the solar cells used were commercial polycrystalline silicon, they are known to be stable over several years. Therefore, in this concept, the degradation of the capacitor is the most critical and fundamental point to verify the durability and reliability of the concept. Although the design and concept demonstration is over the monitoring of the devices will continue, given the importance of these results for future possible industrial applications.
The main objectives of the projects were demonstrated:
1) Transparent thermoelectrics - new photothermal devices were designed and demonstrated, using different layer structures (single layer or multilayer) and/or processing (annealing or not) that allow NIR absorption. A transparent capacitor with up to 0.7 V open circuit voltage and 70% transmittance in the visible range of spectra was demonstrated.
2) Organic solar cells - the possibility of being made under atmospheric conditions and using electrospray was demonstrated. Although performance improvements were still needed, it was possible to demonstrate their integration with transparent capacitors on both rigid and flexible substrates. In addition, the inclusion of sulfide nanoparticles was used to improve the efficiency of the solar cell by about 30% over the initial value.
3) Graphene-based capacitors - these were realized using film application techniques that allow them to be applied directly to solar cells in a stacked graphene-electrolyte-graphene layer. This was possible using a very simple, economical and fast graphite exfoliation method developed during the project.
1) Transparent thermoelectrics - new photothermal devices were designed and demonstrated, using different layer structures (single layer or multilayer) and/or processing (annealing or not) that allow NIR absorption. A transparent capacitor with up to 0.7 V open circuit voltage and 70% transmittance in the visible range of spectra was demonstrated.
2) Organic solar cells - the possibility of being made under atmospheric conditions and using electrospray was demonstrated. Although performance improvements were still needed, it was possible to demonstrate their integration with transparent capacitors on both rigid and flexible substrates. In addition, the inclusion of sulfide nanoparticles was used to improve the efficiency of the solar cell by about 30% over the initial value.
3) Graphene-based capacitors - these were realized using film application techniques that allow them to be applied directly to solar cells in a stacked graphene-electrolyte-graphene layer. This was possible using a very simple, economical and fast graphite exfoliation method developed during the project.