Periodic Reporting for period 1 - FaWB ChaLT (Fabrication of Wide Bandgap Chalcopyrite Photovoltaics at Low Temperatures for Prospective Tandem Solar Cells)
Reporting period: 2022-07-01 to 2024-12-31
The project FaWB ChaLT focuses on the development of wide-bandgap chalcopyrite solar absorber materials and devices for the prospective, new, and innovative chalcopyrite/Si tandem solar cells. These chalcopyrite/Si tandem solar cells can be reliable, cost-effective, and environmentally friendly. For such an innovative tandem cell design, the top cell absorber is made of wide-bandgap chalcopyrite material, and the bottom cell absorber is made of low-bandgap crystalline or multicrystalline Si. However, the experimental demonstration of such a new high-efficiency tandem solar cell device is limited by the fabrication temperature of chalcopyrite materials. In general, chalcopyrite semiconductors are deposited at high temperatures close to 600°C. The use of such high temperatures when creating a monolithic tandem configuration with Si solar cells degrades the bottom Si cell material layers, negatively affecting the overall performance of the resulting tandem solar cell. Another challenge is the use of toxic CdS material in chalcopyrite solar cell devices, which needs to be replaced with an environmentally friendly material. Furthermore, the design aspects of monolithic integration of wide-bandgap chalcopyrite materials with Si cell structures must be improved while overcoming these challenges.
The following are the overall objectives of the project.
(i) Tailor the chalcopyrite absorber composition by incorporating Ag to partially replace Cu, forming the wide-bandgap (Ag, Cu)(In, Ga)Se2. Investigate the role of Ag in reducing the deposition temperature. The first approach is to test the effectiveness of Ag in lowering the deposition temperature of known low-bandgap compositions and then extend the findings to produce advanced wide-bandgap chalcopyrite compositions.
(ii) Replace the traditional toxic CdS buffer layers typically used in chalcopyrite solar cells with alternative environmentally friendly oxide materials.
(iii) Introduce advanced tandem cell architecture to improve the integration of wide-bandgap chalcopyrite with Si structures, avoiding the degradation of Si cell quality.
The following are the overall objectives of the project.
(i) Tailor the chalcopyrite absorber composition by incorporating Ag to partially replace Cu, forming the wide-bandgap (Ag, Cu)(In, Ga)Se2. Investigate the role of Ag in reducing the deposition temperature. The first approach is to test the effectiveness of Ag in lowering the deposition temperature of known low-bandgap compositions and then extend the findings to produce advanced wide-bandgap chalcopyrite compositions.
(ii) Replace the traditional toxic CdS buffer layers typically used in chalcopyrite solar cells with alternative environmentally friendly oxide materials.
(iii) Introduce advanced tandem cell architecture to improve the integration of wide-bandgap chalcopyrite with Si structures, avoiding the degradation of Si cell quality.
The following works have been performed in addressing the identified project objectives.
(i) Chalcopyrite absorbers are deposited using the co-evaporation process. Ag incorporation is achieved through a seed layer approach, enabling the possibility of low-temperature chalcopyrite material deposition.
(ii) Wide-bandgap chalcopyrite devices are produced using environmentally friendly Zn(O,S) buffer layers as an alternative to the traditionally used toxic CdS.
(iii) A practical approach for integrating wide-bandgap chalcopyrites with Si for monolithic tandem solar cell design is established
(i) Chalcopyrite absorbers are deposited using the co-evaporation process. Ag incorporation is achieved through a seed layer approach, enabling the possibility of low-temperature chalcopyrite material deposition.
(ii) Wide-bandgap chalcopyrite devices are produced using environmentally friendly Zn(O,S) buffer layers as an alternative to the traditionally used toxic CdS.
(iii) A practical approach for integrating wide-bandgap chalcopyrites with Si for monolithic tandem solar cell design is established
Working towards the project objectives the following results have been obtained beyond the state of the art.
(i) While Ag incorporation has proven effective in reducing the deposition temperature of chalcopyrite materials, particularly in low-bandgap compositions—aligning with existing literature—the project's results demonstrate that even a minor Ag incorporation of as little as 0.5–1.4 at% is sufficient to achieve this effect, surpassing the state of the art. Furthermore, a complete material-level transformation occurring with such minimal Ag incorporation and its implications for the open-circuit voltage of chalcopyrite solar cells have been demonstrated, also exceeding the state of the art. A publication for the same can be found at https://doi.org/10.1002/solr.202400863(opens in new window).
(ii) The implementation of a Zn(O,S) buffer layer deposited via a scalable sputtering process in wide-bandgap chalcopyrite solar cells has yielded 80-95% quantum efficiency over a broad absorption range within the absorption limits set by the chalcopyrite absorber’s bandgap. The Zn(O,S) bufferlayer has been proven to be an effective, environmentally friendly alternative to the traditionally used toxic CdS yielding competing photoconversion efficiency for the wide-bandgap chalcopyrite devices.
(iii) An innovative monolithic configuration for (wide-bandgap chalcopyrite)/Si tandem architecture has been demonstrated while preserving the carrier lifetime of the bottom Si cell structure. A patent application has been filed to support this invention.
(i) While Ag incorporation has proven effective in reducing the deposition temperature of chalcopyrite materials, particularly in low-bandgap compositions—aligning with existing literature—the project's results demonstrate that even a minor Ag incorporation of as little as 0.5–1.4 at% is sufficient to achieve this effect, surpassing the state of the art. Furthermore, a complete material-level transformation occurring with such minimal Ag incorporation and its implications for the open-circuit voltage of chalcopyrite solar cells have been demonstrated, also exceeding the state of the art. A publication for the same can be found at https://doi.org/10.1002/solr.202400863(opens in new window).
(ii) The implementation of a Zn(O,S) buffer layer deposited via a scalable sputtering process in wide-bandgap chalcopyrite solar cells has yielded 80-95% quantum efficiency over a broad absorption range within the absorption limits set by the chalcopyrite absorber’s bandgap. The Zn(O,S) bufferlayer has been proven to be an effective, environmentally friendly alternative to the traditionally used toxic CdS yielding competing photoconversion efficiency for the wide-bandgap chalcopyrite devices.
(iii) An innovative monolithic configuration for (wide-bandgap chalcopyrite)/Si tandem architecture has been demonstrated while preserving the carrier lifetime of the bottom Si cell structure. A patent application has been filed to support this invention.