Periodic Reporting for period 1 - TERASUN (Towards Terawatt Production of c-Si Solar Photovoltaics)
Periodo di rendicontazione: 2024-06-01 al 2025-11-30
The overall objectives of the TERASUN project are threefold:
**Objective #1** - Boosting the power conversion efficiency (PCE) of silicon heterojunction (SHJ) solar cells. The project aims to achieve this objective by increasing the amount of light captured by the crystalline silicon (c-Si) wafer. To this end both plasma-based dry etching and wet chemical etching process are developed to improve the surface structure and augment the light trapping. Another approach to capture more light is addressed through the structuration of the module cover glass, including an anti-reflective coating. Furthermore, the project strives to avoid the use of critical raw materials such as silver (Ag) and indium (In). Therefore Ag-free metallisation based on copper (Cu) plating is developed holding the potential for high throughput and gains in PCE due to improved contact properties and reduced shading. Also, In-free transparent conductive oxides (TCO) are developed, namely aluminium-doped zinc oxide (AZO) and tin oxide (SnO2), applied either by slot-die coating and curing (AZO) or the state-of-the-art sputtering technique (AZO and SnO2). Here the benefit mainly relies on the avoidance of the use of In. And finally, novel passivating contacts are developed employing thermally evaporated or sputtered molybdenum oxide (MoOx) that are to be used in interdigitated back-contacted (IBC) SHJ devices with a potential for very high efficiencies due to the elimination of shading and absorption losses [EÖ1.1][JS1.2][EÖ1.3][EÖ1.4]at the front side of the devices (metallisation at the rear only).
**Objective #2** - Combination of new components in photovoltaic (PV) cells and modules. This second objective is closely aligned with Objective #1, and aims to integrate the developed components into devices, i.e. solar cells and modules.
**Objective #3** - Provide clear direction for technology roadmap for policymakers and industry. This final objective is to develop the TERASUN Decision Support Tool for industrial stakeholders and policymakers. The goal is to provide a tool that merges three types of information: (1) environmental impact through lifecycle assessment data, (2) economic impact through lifecycle costing data, and (3) potential gains in performance (PCE) for solar cells and modules using the TERASUN components.
**Objective #1** - Boosting the power conversion efficiency (PCE) of silicon heterojunction (SHJ) solar cells. The project aims to achieve this objective by increasing the amount of light captured by the crystalline silicon (c-Si) wafer. To this end both plasma-based dry etching and wet chemical etching process are developed to improve the surface structure and augment the light trapping. Another approach to capture more light is addressed through the structuration of the module cover glass, including an anti-reflective coating. Furthermore, the project strives to avoid the use of critical raw materials such as silver (Ag) and indium (In). Therefore Ag-free metallisation based on copper (Cu) plating is developed holding the potential for high throughput and gains in PCE due to improved contact properties and reduced shading. Also, In-free transparent conductive oxides (TCO) are developed, namely aluminium-doped zinc oxide (AZO) and tin oxide (SnO2), applied either by slot-die coating and curing (AZO) or the state-of-the-art sputtering technique (AZO and SnO2). Here the benefit mainly relies on the avoidance of the use of In. And finally, novel passivating contacts are developed employing thermally evaporated or sputtered molybdenum oxide (MoOx) that are to be used in interdigitated back-contacted (IBC) SHJ devices with a potential for very high efficiencies due to the elimination of shading and absorption losses [EÖ1.1][JS1.2][EÖ1.3][EÖ1.4]at the front side of the devices (metallisation at the rear only).
**Objective #2** - Combination of new components in photovoltaic (PV) cells and modules. This second objective is closely aligned with Objective #1, and aims to integrate the developed components into devices, i.e. solar cells and modules.
**Objective #3** - Provide clear direction for technology roadmap for policymakers and industry. This final objective is to develop the TERASUN Decision Support Tool for industrial stakeholders and policymakers. The goal is to provide a tool that merges three types of information: (1) environmental impact through lifecycle assessment data, (2) economic impact through lifecycle costing data, and (3) potential gains in performance (PCE) for solar cells and modules using the TERASUN components.
**Advanced Light Management**: In order to increase the texturization of crystalline silicon wafers, we made progress in developing both dry (plasma) and wet chemical etching processes, aimed at maximising light absorption within photovoltaic cells. The plasma-based process has demonstrated a potential short-circuit current density (Jsc) gain of up to 3.72 mA/cm².
**Ag-free Metallisation**: Promising results have been obtained for double-side copper-plated silicon heterojunction (SHJ) devices, with fill factor (FF) values >81% and power conversion efficiency (PCE) >23%. This was achieved through optimisation in seed layer structuring and electrolytes, demonstrating a viable pathway to replace silver.
**Indium-free Transparent Conductive Oxides (TCOs)**: Development of alternative TCO materials is advancing on two fronts. Aluminium-doped zinc oxide (AZO) layers have been successfully deposited via slot-die coating for initial passivation tests. Furthermore, promising opto-electrical properties have been achieved with sputtered materials (tin oxide, SnO2 and AZO). Initial integration of an optimised AZO/SiN stack into the front side of SHJ cells has yielded a PCE of 23.54%, comparable to the indium-based reference.
**Novel Passivating Contacts**: The development of molybdenum oxide (MoOx) layers using both sputtering and thermal evaporation has been successful. Lab-scale devices employing thermally evaporated MoOx have achieved a high PCE of 23.94%. Newly developed wet-chemical textures have also been successfully passivated, with implied open-circuit voltages (Voc) reaching up to 747 mV.
**Decision Support Tool (DST)**: The development of the TERASUN Decision Support Tool (DST) is underway, including the establishment of its core logic, database structure, and the framework for integrating life-cycle assessment (LCA) and life-cycle costing (LCC) data. Progress has been made on the non-technical, data-centric aspects of the project.
**Ag-free Metallisation**: Promising results have been obtained for double-side copper-plated silicon heterojunction (SHJ) devices, with fill factor (FF) values >81% and power conversion efficiency (PCE) >23%. This was achieved through optimisation in seed layer structuring and electrolytes, demonstrating a viable pathway to replace silver.
**Indium-free Transparent Conductive Oxides (TCOs)**: Development of alternative TCO materials is advancing on two fronts. Aluminium-doped zinc oxide (AZO) layers have been successfully deposited via slot-die coating for initial passivation tests. Furthermore, promising opto-electrical properties have been achieved with sputtered materials (tin oxide, SnO2 and AZO). Initial integration of an optimised AZO/SiN stack into the front side of SHJ cells has yielded a PCE of 23.54%, comparable to the indium-based reference.
**Novel Passivating Contacts**: The development of molybdenum oxide (MoOx) layers using both sputtering and thermal evaporation has been successful. Lab-scale devices employing thermally evaporated MoOx have achieved a high PCE of 23.94%. Newly developed wet-chemical textures have also been successfully passivated, with implied open-circuit voltages (Voc) reaching up to 747 mV.
**Decision Support Tool (DST)**: The development of the TERASUN Decision Support Tool (DST) is underway, including the establishment of its core logic, database structure, and the framework for integrating life-cycle assessment (LCA) and life-cycle costing (LCC) data. Progress has been made on the non-technical, data-centric aspects of the project.
As described in the previous section ("Work performed and main achievements"), the TERASUN project already pushed the boundaries of the state-of-the-art across all the activities. Improved wafer surface textures developed in the project may help to significantly increase the current output of SHJ devices, given that efficient surface passivation can be ensured. This remains to be demonstrated in the second part of the project. The development of the Cu plating processes made significant progress also with respect to the simultaneous metallisation of both sides of the solar cell. Regarding the development of novel passivating contacts promising results have been obtained and will be tested in IBC devices in the second half of the project. Besides, excellent surface passivation has been achieved with newly developed wet-chemical textures that have the potential to enable high performance devices.