Dual‐Use Self‐Assembled Monolayer Controlling Charge Carrier Extraction in Organic Solar Cells

Abstract

The development and use of interface materials are essential to the continued advancement of organic solar cells (OSCs) performance. Self‐assembled monolayer (SAM) materials have drawn attention because of their simple structure and affordable price. Due to their unique properties, they may be used in inverted devices as a modification layer for modifying ZnO or as a hole transport layer (HTL) in place of typical poly(3,4‐ethylenedioxythiophene)‐poly(styrenesulfonate) (PEDOT:PSS) in conventional devices. In this work, zinc oxide (ZnO) is modified using five structurally similar SAM materials. This resulted in a smoother surface, a decrease in work function, a suppression of charge recombination, and an increase in device efficiency and photostability. In addition, they can introduced asfor hole extraction layer between the active layer and MoO3, enabling the use of the same material at several functional layers in the same device. Through systematic orthogonal evaluation, it is shown that some SAM/active layer/SAM combinations still offered device efficiencies comparable to ZnO/SAM, but with improved device’ photostability. This study may provide recommendations for future SAM material's design and development as well as a strategy for boosting device performance by using the same material across both sides of the photoactive layer in OSCs.

Self-Assembled Monolayer Engineered ZnO Electron Transport Layer to Improve the Photostability of Organic Solar Cells

“…This could significantly suppress photo-oxidation at the ZnO/active layer interfaces, enhancing device stability and PCE of the i-OSCs. , Furthermore, atomic force microscopy (AFM) studies revealed root-mean-square (RMS) roughness values of 2.24, 1.54, and 1.58 nm for the pristine, ODT-treated, and OTMS-treated ZnO films, respectively, suggesting a smoother surface morphology for SAM-modified ZnO films compared to the pristine film (see Figure S1). These findings suggest successful coverage of the ZnO surface by an ultrathin layer formed by the thiolate and silane ligands, which significantly reduced the surface roughness as evidenced by the AFM results …”

“…17,18 Recently, self-assembled monolayers (SAMs) have emerged as a promising strategy for modifying metal and metal oxide surfaces in OSCs. 19,20 The main effect caused by applying SAMs to metal-oxide surfaces is the formation of interfacial dipoles, which can assist with electron extraction and enhance performance. SAMs have been successfully employed as interface modifiers between the metal oxide and active layers in OSC devices, achieving a record PCE of 18.4% 21 and an extrapolated lifetime of 20 years.…”

“…These findings suggest successful coverage of the ZnO surface by an ultrathin layer formed by the thiolate and silane ligands, which significantly reduced the surface roughness as evidenced by the AFM results. 20 To understand the mechanism behind the improved morphology, we employed density functional theory (DFT) calculations using the 6-31G* basis set and B3LYP level of theory in Gaussian16 software. These calculations revealed dipole moments of 1.6 and 1.4 D for ODT and OTMS SAM molecules, respectively.…”

“…Doping ZnO with metals such as lithium (Li), magnesium (Mg), and tin (Sn) yields remarkable improvements in electron mobility and energy-level alignment. As a result, electron transport and collection are noticeably enhanced. − Nonconjugated polymers such as polyethylenimine (PEI) and ethoxylated polyethylenimine (PEIE) have been recognized as promising candidates for modifying the surface of ZnO because these polymers offer enhanced photostability. , Recently, self-assembled monolayers (SAMs) have emerged as a promising strategy for modifying metal and metal oxide surfaces in OSCs. , The main effect caused by applying SAMs to metal-oxide surfaces is the formation of interfacial dipoles, which can assist with electron extraction and enhance performance. SAMs have been successfully employed as interface modifiers between the metal oxide and active layers in OSC devices, achieving a record PCE of 18.4% and an extrapolated lifetime of 20 years .…”

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

“…Organic solar cells (OSCs) have garnered considerable attention due to their merits including being flexible, lightweight, and solution-processable for manufacturing. − Recently, the maximum power conversion efficiency (PCE) of single-junction OSCs has approached nearly 20%, which is attributed to the emergence of nonfullerene photovoltaic materials together with the continuous optimization of device engineering. − A typical OSC is structured by two electrodes sandwiching a photoactive layer with hole (HTL) and electron (ETL) transport layers between their interfaces, in which the photoactive layer determines light-harvesting and free-carrier production, while the HTL/ETL play a vital role in carrier transport and long-term operational stability. − …”