Self-Assembly Metal Chelate as Ultraviolet Filterable Interface Layer for Efficient Organic Solar Cells

Interface engineering plays a vital role in the further improvement of efficiency and stability for organic solar cells (OSCs). Herein, a self-assembly metal chelate based on hafnium and a designed ligand, N-(4-(3-oxobutanoyl)phenyl)acetamide (ACBN) is applied as both interfacial modification layer and UV-light filter in OSCs. The strong hydrogen-bond induced intermolecular interaction enables Hf(ACBN)(4) with the prerequisite of adequate solvent resistance to work as an electron transport layer (ETL) in the inverted OSCs. The self-assembly behavior of Hf(ACBN)(4) on the SnO2 film surface via constructing compact coordination structure has been verified via systematic theory calculations. In addition to optimizing the energy level alignment, the Hf(ACBN)(4) modification effectively passivates the surface defect of SnO2 films for less surface charge recombination and a more efficient charge collection process. Thus, the OSCs with Hf(ACBN)(4) layer yield a maximum PCE of 18.1%, better than that based on the bare SnO2 layer. Moreover, beneficial from the reduced oxygen vacancies via coordination effect and the UV-light filter function of Hf(ACBN)(4), the OSCs based on SnO2/ Hf(ACBN)(4) composite ETL exhibit preferable stabilities under UV-light irradiation or continuous operational conditions.