Perylene Diimide‐Based Low‐Cost and Thickness‐Tolerant Electron Transport Layer Enables Polymer Solar Cells Approaching 19% Efficiency

Abstract

The materials for electron transport layers (ETLs) play a significant role in the performance of polymer solar cells (PSCs) but face challenges, such as low electron transport mobility and conductivity, low solution processibility, and extreme thickness sensitivity, which will undermine the photovoltaic performance and hinder compatibility of large‐scale fabrication technique. To address these challenges, a new n‐type perylene diimide‐based molecule (PDINB) with two special amine‐anchored long‐side chains is designed and synthesized feasibly. PDINB shows very high solubility in common organic solvents, such as dichloromethane (>75 mg ml−1) and methanol with acetic acid as an additive (>37 mg ml−1), which leads to excellent film formability when deposited on active layers. With PDINB as ETLs, the photovoltaic performance of the PSCs is boosted comprehensively, leading to power conversion efficiency (PCE) up to 18.81%. Thanks to the strong self‐doping effect and high conductivity of PDINB, it displays an appreciable thickness‐tolerant property as ETLs, where the devices remain consistently high PCE values with the thickness varying from 5 to 30 nm. Interestingly, PDINB can be used as a generic ETL in different types of PSCs including non‐fullerene PSCs and all‐polymer PSCs. Therefore, PDINB can be a potentially competitive candidate as an efficient ETL for PSCs.

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

“…PDINN-NOPN and PDI-4NOPN exhibit a deeper HOMO than PDINN, which can effectively block hole transfer from the donor to the electrode and avoid exciton recombination. This possesses a virtual effect on improving the photovoltaic performance of OSCs. , …”

“…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. ,, …”

“…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) . 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 .…”