HIGHLIGHTED RESEARCH
When sunlight hits a solar cell, it sends some of the light energy into the cell. The solar cell then turns this light energy into electricity. However, some of the light energy goes into other parts of the cell, and is lost very fast and the remaining energy gets extracted. In this paper we explain our idea to slow this down this fast energy loss, making it possible to capture it, allowing solar cells to be more efficient.
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By tuning the cascade energy transfer in quasi-2D perovskite (that contains many layered phases), the carriers in the material created by light lose their energy (called excess energy) much slower than usual (up to two orders of magnitude slower compared to common 3D perovskites). The slower relaxation allows time for the carriers to be extracted before the excess energy is lost, which means that using this approach solar cells can be made more efficient.
Importantly, the material composition can lead to 'quantum effects' in the energy cascade that make it faster: a shorter organic spacer molecule can coherently delocalize the excitation among layered phases for more efficient energy cascade. This will ultimately limit carrier extraction, telling us that in this approach the material composition needs to be designed prudently.
2D materials like lead halide Ruddlesden-Popper perovskites (RPP), have a structure like a stack of sandwiches, with alternating organic and inorganic layers. The sandwich layers are really thin and really close together. The layers are so close together that they can share their electrons. This means that if one layer is excited by light, it can give the energy to an adjoining layer very quickly. This is important because it means that we might be able to use this material to make more efficient solar panels and other devices that use light.
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We explain the unique optical properties of RPP considering them as a superlattice of finite-potential quantum wells (like a sandwich stack). Using our approach, we trace the origin of the ultrafast energy transfer in them to wavefunction delocalization across the quantum well barriers (which are the organic molecules), giving the important message that the organic molecule can actually tune properties in these materials.