Coordination nanostructures for high performing solar cells Kezia Sasitharan Newcastle University, UK This work highlights the role of nano-structured metal-organic coordination polymers (CPs) in opto-electronic applications such as solar cells for enhanced device performance. CPs have emerged as promising materials which allow the creation of diverse, well defined architectures with tailored properties. They are versatile and can be prepared either in the form of free standing 2D nanosheets, or 1D nanowires, which means they can be easily integrated into device architectures. These free standing materials possess a high ordered structure of inorganic materials combined with the chemically tailorable properties and low cost of organics. Thanks to their high external surface area, aspect ratios, nanoscopic dimensions and novele electronic and optical properties, CPs have been found to outperform their precursors and other inorganic low dimensional materials in a wide range of applications. As a pioneering contribution in the field, I with my colleagues from Sheffieldpreviously reported the first example showing incorporation of 2D CPs known as Metal-organicnanosheets (MONs)into the photoactive layer of organic solar cells.Zinc-porphyrin based MONs were added to an archetypal organic solar cell architecture through a simple spin-coating method to create a ternary blend solar cell resulting in a near doubling in device power conversion efficiency (PCE) from 2.7% to 5.2%.Detailed investigations into the morphology of the active layer showed that the relative proportion of crystalline regions in the thin films is improved upon incorporation of MONs leading to improved current density (J SC ). We recently reported the the effect of adding MONs to the active layer of six different organic solar cell devices. Devices based on amorphous polymer donor-systems benefitted from the additional light-absorption of the porphyrin units in MONs, which lead to small increases in the deviceJ SC . However, semi-crystalline polymer systems showed remarkable improvements with enhancedcrystallinity and charge transport. Most remarkably, a power conversion efficiency of 12.3% was achieved which—to the best of our knowledge—is the highest reported fullerene-based organic solar cell. These results establish the templating effect of MONs as a general approach to improve the performance of semi-crystalline polymer-based devices. We believe that it should also be possible to engineer CPs that act as electron donors in different types of solar cells. Enhanced ordering and crystallinity are also desirable properties in other classes of solar cells and CPs hold significant potential as additives to create a new generation of electronic devices having improved performance. CPs with engineered energy levelsaligning withthe photoactive layer can also be used as charge transport layers in perovskite and other solar cells. Currently, at Newcastle I am exploring the role of 1D CP nanowires as hole transport materials in solid state dye-sensitized solar cells, demonstratingthe versatility and wider applicability of CPs for improved performance in emerging solar cell technologies. References
1. Sasitharan, K.,et alAdv. Sci.2022,9, 2200366. 2. Sasitharan K., et al J Mat Chem A 2020,,8,6067.
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