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Hierarchically Engineered Inorganic Nanomaterials from the atomic to supra-nanocrystalline level as a novel platform for SOLution Processed SOLar cells

Periodic Reporting for period 4 - HEINSOL (Hierarchically Engineered Inorganic Nanomaterials from the atomic to supra-nanocrystalline level as a novel platform for SOLution Processed SOLar cells)

Reporting period: 2021-08-01 to 2022-01-31

The control and engineering of the optoelectronic properties of colloidal nanocrystal and quantum dot solids underpins the performance of optoelectronic devices and solar cells that can be produced in low cost and large scale from such a material platform. Solution processed optoelectronics can bring about a revolution in a large spectrum of critical applications ranging from biomedical imaging, spectroscopy, night vision, surveillance and of course photovoltaics. All the above is of paramount importance for they address critical societal needs on health monitoring, safety and security as well as renewable energies. The lack of engineering methodologies of such materials has limited the report of highly performant devices and solar cells, produced thereof, to being based on Pb and Cd containing nanocrystals. One of the primary goals of HEINSOL has been to investigate and develop advanced engineering methodologies from the atomic to the supra-nanocrystalline levels of such materials and devices in order to reach performance that was previously considered unreachable and further to employ such methodologies in materials that comprise non-toxic and Earth abundant elements to allow facile commercialization of this technology in the future with minimal regulatory concerns. Moreover HEINSOL has explored new synthetic routes for such materials that minimize their manufacturing cost and are compatible with large scale volume manufacturing as well as make use of chemicals (solvents, precursors) that are less harmful to the environment and of lower cost in order to further reduce manufacturing costs of the materials employed in the devices. Rendering solution processed nanocrystal technologies competitive in performance for consumer electronics and eliminating RoHS restrictions enables their facile market uptake and provides access to applications that had been considered to date impossible given the cost and low-volume manufacturing of currently available technologies. In the field of photovoltaics the introduction of envirnomentally frienldy materials and PV production thereor unleashes the potential of solar harvesting towards ubiquitous integration with consumer and portable devices for IoT applications, building or car integrated photovoltaics and further eliminates the needs for expensive closed-cycle reycling and disposal of heavy metal toxic elements. The above bring about significant benefits to society at large towards a cleaner and more sustainable economy and will boost the European manufacturing roadmap based on this new generation of materials and optoelectronic and photovoltaic devices.
Heinsol has thus far made important contributions to this end as we have developed novel approaches in colloidal quantum dot and nanocrystal devices with record low trap state densities by simultaneously passivating defects chemically (at the atomic level) and electronically (at the suprananocrystalline level). HEINSOL has demonstrated new ways of engineering nanocomposite structures comprising colloidal quantum dots by control of their energetic landscape and their density of states reaching record performance in infrared LEDs and solar cells. We have also shown that by combining 2D materials with colloidal quantum dots can reach to very high efficiency low cost tandem solar cells. On the other hand, we have further explored and synthesized novel semiconducting metal chalcogenide nanocrystals and quantum dots that are free of Pb and Cd and we envision to apply our developed engineering methodologies to those new materials towards environmentally friendly low cost solar cells. So far, we have further developed synthetic protocols for such environmentally free materials to enable low cost large scale production in the absence of needs for vacuum and high temperatures in order to increase also the manufacturing readiness level of this technology. We have indeed demonstrated solar cells based on AgBiS2 colloidal nanocrystals that are synthesized at room temperature in ambient conditions, with power conversion efficiency on par with that reported from such material produced previously using high temperature and vacuum-based hot injection techniques. By engineering such nanocrystals at the atomic level we have developed a material that exhibits the highest optical absorption among materials developed to date for solar cells. By doing so and by further optimizing surface passivation and device structure engineering we have reported the most efficient ultra-thin film solution processed solar cell [Nat. Photon. 16, 235–241 (2022)]. In the process of discovering new strategies of electronic doping of such materials we have realized the implications in adjacent application fields and have demonstrated the first solution processed Silicon compatible infrared laser opening new paths towards silicon photonics, low-cost LIDAR and optical communication applications [Nat. Photon. 15, 738–742 (2021)]. Last but not least, HEINSOL discovered new ways of controlling optoelectronic properties of quantum dots by engineering the energetic potential landscape at the supra-nanocrystalline level. This created a paradigm shift in designing and optimizing colloidal quantum dot optoelectronic devices. We have exploited those finding to produce colloidal quantum dot solar cells with open circuit voltage approaching the radiative limit and light emitting diodes with record high performance in the short-wave infrared. The latter allows the introduction of a new low-cost CMOS compatible LED technology with applications ranging from automotive safety to 3D imaging and biomedical and spectroscopy for health, environmental and product quality inspection [Nature Nanotech 14, 72–79 (2019)].
HEINSOL will push the limits of engineering such complex materials and demonstrate real-world high performance devices made of this low cost material platform. In doing so, HEINSOL will discover new physics and mechanisms at play in the nanoscale that in turn may lead to novel device functionalities and performance records not only in solar cells but also in light emitters and lasers. At the same time HEINSOL will develop the synthesis of materials in the colloidal nanocrystal form that had not been explored before and that are based on environmentally friendly elements paving the way for bringing this technology closer to the consumer market