Abstract
The open circuit voltage (VOC) deficit in perovskite solar cells (PSCs) is greater in wide bandgap (>1.7 eV) cells than in ~1.5 eV perovskites.1,2 Quasi-Fermi level splitting (QFLS) measurements reveal VOC-limiting recombination at the electron transport layer (ETL) contact.3-5 This, we find, stems from inhomogeneous surface potential and poor perovskite-ETL energetic alignment. Common monoammonium surface treatments fail to address this; instead we introduce diammonium molecules to modify the perovskite surface states and achieve a more uniform spatial distribution of surface potential. Using 1,3-propane diammonium (PDA), QFLS increases by 90 meV, enabling 1.79 eV PSCs with a certified 1.33 V VOC, and > 19% power conversion efficiency (PCE). Incorporating this layer into a monolithic all-perovskite tandem, we report a record VOC of 2.19 V (89% of the detailed balance VOC limit) and > 27% PCE (26.3% certified quasi-steady-state). These tandems retain more than 86% of their initial PCE after 500 hrs operation.
This research was made possible by the US Department of the Navy, Office of Naval Research Grant (N00014-20-1-2572 and N00014-20-1-2725), the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE) under the Solar Energy Technologies Office Award Number DE-EE0008753. This work was supported in part by the Ontario Research Fund-Research Excellence program (ORF7-Ministry of Research and Innovation, Ontario Research Fund-Research Excellence Round 7). This work was also supported by the King Abdullah University of Science and Technology (KAUST) under Award No. OSR-CRG2020-4350. This work was authored in part by the National Renewable Energy Laboratory, operated by Alliance for Sustainable Energy, LLC , for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. NREL authors acknowledge support from Operational Energy Capability Improvement Fund (OECIF) of the Department of Defense. The views expressed in the article do not necessarily represent the views of the DOE or the U.S. Government. The CLS is funded by NSERC, the Canadian Institutes of Health Research, CFI, the Government of Saskatchewan, Western Economic Diversification Canada, and the University of Saskatchewan. This work was also supported by the Natural Sciences and Engineering Council of Canada and the Vanier Canada Graduate Scholarship. .The authors thank Dr. Jonathan Warby for a useful discussion that contributed to our understanding of perovskite/ETL interfaces and Tao Song and Nikos Kopidakis at NREL for device certification. Z.W. acknowledges the Banting Postdoctoral Fellowships Program of Canada. GIWAXS patterns were collected at the BXDS-WLE Beamline at the Canadian Light Source (CLS) with the assistance of Dr. Chang-Yong Kim and Dr. Adam Leontowich.