Brominated Quaternary Ammonium Salt-Assisted Hybrid Electron Transport Layer for High-Performance Conventional Organic Solar Cells

Abstract

Interlayer engineering is crucial for achieving efficient and stable organic solar cells (OSCs). Herein, by introducing a commercialized brominated quaternary ammonium salt, hexamethonium bromide (HB), into a perylene diimide (PDI)-structured electron transport layer (ETL), a PDINN:HB hybrid ETL with enhanced charge collection ability and environmental/operational stability is realized. Molecular dynamics simulations and Kelvin probe force microscopy indicate that strong polar bromine and amine groups can form extra interfacial dipoles in the hybrid interlayer, while X-ray photoelectron spectroscopy and electron paramagnetic resonance suggest the hybrid ETL can interact with the Ag cathode, thereby regulating the energy level arrangement at the interface. As for the results, the PDINN:HB hybrid ETL enables improved power conversion efficiency (PCE) from 17.8 to 18.4% and 18.8 to 19.4% in PM6:C5-16 bulk heterojunction-and PM6/L8-BO pseudobulk heterojunction-based OSCs, respectively. The versatility of this method is further verified by introducing a range of brominated quaternary ammonium salts into PDINN, in which a superior PCE and stability are all obtained compared to the reference device.

Synergistically Modulating the Bay and Amid Sites of a Perylene Diimide Cathode Interface Layer for High-Efficiency and High-Stability Organic Solar Cells

“…Thus, it is imperative to substantially enhance the stability without sacrificing the remarkable PCE. As a primary composition in OSCs, the cathode interface layers (CILs) possess a momentous function in tuning the work function ( W f ), optimizing interface contact, and improving the properties of the OSCs. − The capacity of adjusting W f is closely related to the doping, interfacial dipole, and polar groups. − , Compared to the inorganic CIL (LiF, TiO x , and ZnO, etc. ), the organic CIL has a considerable number of applications because of its favorable interfacial dipole for ohmic contact, eco-friendly solution processing, excellent morphology, and stability. − Hence, numerous n-type organic semiconductors have been progressed for the efficient CILs, for instance, amine-functionalized polyfluorenes (PFN and PFN-Br), , N-oxide amine (PDINO), aliphatic amine or bay -functionalized PDI derivatives (PDINB, PDINN, H75), ,, and hydroxylated PDI (PDI-Br-0O, PDI-Br-1O, and PDI-Br-3O) .…”

“…), the organic CIL has a considerable number of applications because of its favorable interfacial dipole for ohmic contact, eco-friendly solution processing, excellent morphology, and stability. − Hence, numerous n-type organic semiconductors have been progressed for the efficient CILs, for instance, amine-functionalized polyfluorenes (PFN and PFN-Br), , N-oxide amine (PDINO), aliphatic amine or bay -functionalized PDI derivatives (PDINB, PDINN, H75), ,, and hydroxylated PDI (PDI-Br-0O, PDI-Br-1O, and PDI-Br-3O) . Moreover, inserting a quaternary ammonium salt in the PDI derivates can form extra interfacial dipoles and further adjust the performance of OSCs owing to their strong polar bromine and amine groups . Consequently, numerous PDI-based small molecules are developed and applied as high-performance CILs due to their exceptional electron transfer properties and appropriate energy levels for abstracting electrons, ,,− whereas CILs with hydrophilic polar side chains are vulnerable to moisture erosion, which makes CILs obtain high surface energies (γ s ) and interfacial energies (γ ac ) and possess a poor inferior interfacial link with the active layer, ultimately affecting the PCE and stability of the device. − Besides, the highly coplanar PDI core can generate unconscionable molecular aggregation, leading to a rough interface morphology and a high obstacle for electron extraction, finally hindering further elevation in the performances of OSCs. , With these concerns, in numerous studies, some bay -functionalized PDI-based CILs have been reported to tune aggregation and energy levels to meet the excellent properties of OSCs. , However, the problems of stability and PCE are rarely addressed simultaneously.…”

“…Moreover, inserting a quaternary ammonium salt in the PDI derivates can form extra interfacial dipoles and further adjust the performance of OSCs owing to their strong polar bromine and amine groups . Consequently, numerous PDI-based small molecules are developed and applied as high-performance CILs due to their exceptional electron transfer properties and appropriate energy levels for abstracting electrons, ,,− whereas CILs with hydrophilic polar side chains are vulnerable to moisture erosion, which makes CILs obtain high surface energies (γ s ) and interfacial energies (γ ac ) and possess a poor inferior interfacial link with the active layer, ultimately affecting the PCE and stability of the device. − Besides, the highly coplanar PDI core can generate unconscionable molecular aggregation, leading to a rough interface morphology and a high obstacle for electron extraction, finally hindering further elevation in the performances of OSCs. , With these concerns, in numerous studies, some bay -functionalized PDI-based CILs have been reported to tune aggregation and energy levels to meet the excellent properties of OSCs. , However, the problems of stability and PCE are rarely addressed simultaneously. Therefore, more efficient and stable PDI-based CILs need to be explored. ,, …”