High-Efficiency Nonfullerene Organic Solar Cells Enabled by Atomic Layer Deposited Zirconium-Doped Zinc Oxide

Organic solar cells (OSCs) are promising photovoltaic devices and zinc oxide (ZnO) is a commonly used electron transport layer (ETL) in OSCs. However, the conventional spin-coating ZnO layer is currently limiting its efficiency potential. Herein, it is shown for the first time that atomic layer deposition (ALD), which allows for controlled thin film growth with atomic-scale control, can effectively be used to optimize the ZnO for nonfullerene OSCs. First, density functional theory (DFT) calculations are discussed to show the impact of doping ZnO with zirconium (Zr) on its density of states and detail the synthesis of Zr doped ZnO films by ALD using a supercycle approach. A 2.4% Zr concentration is found to be optimal in terms of optoelectronic properties and sufficiently low defect density. The champion efficiency of 14.7% for a PM6:N3-based nonfullerene OSC with Zr-doped ZnO ETL are obtained, which is approximate to 1% absolute higher compared to a device with an undoped ZnO ETL. This improvement is attributed to a lower series resistance, a suppressed surface recombination, and an enhanced current extraction resulting from the Zr-doped ZnO. This work demonstrates the potential of atomic-scale engineering afforded by ALD towards achieving the ultimate efficiency of OSCs.