Tailoring the Energy Manifold of Quasi-Two-Dimensional Perovskites for Efficient Carrier Extraction

Harvesting the excess energy from absorbed above bandgap photons is a promising approach to overcome the detailed balance limit for higher solar cell efficiencies. However, this remains very challenging for 2D layered halide perovskites as the fast excess energy loss competes effectively with charge extraction. Herein, the authors engineer the energy cascade manifold of quantum well (QW) states in quasi-2D Ruddlesden–Popper perovskites by facile tuning of the organic spacer to decelerate the energy loss. The resulting excess energy loss rate is up to two orders slower compared to 3D perovskites, thus enabling efficient carrier extraction. 2D electronic spectroscopy reveals further insights into the structural and energetic disorder of these layered systems. Importantly, a judicious choice of the organic spacer holds the key to tailoring the coherent coupling between QWs that strongly influences the competition between the energy cascade and charge extraction. Ministry of Education (MOE) National Research Foundation (NRF) Accepted version The authors acknowledge Dr. Teddy Salim from the Facility for Analysis Characterization Testing and Simulation (FACTS), School of Material Science and Engineering, Nanyang Technological University, for the UPS measurement. This research/project was supported by the Ministry of Education under its AcRF Tier 2 grants (MOE2019-T2-1-006, MOE2019-T2-1-097, and MOE-T2EP50120-0004); and the National Research Foundation (NRF) Singapore under its NRF Investigatorship (NRF-NRFI-2018-04). E.C. acknowledges the “CQ-TECH” STARS Grant 2019 (2019-UNPD0Z9-0166571). E.F. acknowledges a Ph.D. fellowship from the Department of Excellence program “NExuS.