Mitigating Detrimental Effect of Self‐Doping Near the Anode in Highly Efficient Organic Solar Cells

Abstract

Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) has been one of the most established hole transport layers (HTL) in organic solar cells (OSCs) for several decades. However, the presence of PSS − ions is known to deteriorate device performance via a number of mechanisms including diffusion to the HTL-active layer interface and unwanted local chemical reactions. In this study, it is shown that PSS − ions can also result in local p-doping in the high efficiency donor:non-fullerene acceptor blendsresulting in photocurrent loss. To address these issues, a facile and effective approach is reported to improve the OSC performance through a two-component hole transport layer (HTL) consisting of a self-assembled monolayer of 2PACz ([2-(9H-Carbazol-9-yl)ethyl]phosphonic acid) and PEDOT:PSS. The power conversion efficiency (PCE) of 17.1% using devices with PEDOT:PSS HTL improved to 17.7% when the PEDOT:PSS/2PACz two-component HTL is used. The improved performance is attributed to the overlaid 2PACz layer preventing the formation of an intermixed p-doped PSS − ion rich region (≈5-10 nm) at the bulk heterojunction-HTL contact interface, resulting in decreased recombination losses and improved stability. Moreover, the 2PACz monolayer is also found to reduce electrical shunts that ultimately yield improved performance in large area devices with PCE enhanced from 12.3% to 13.3% in 1 cm 2 cells.

Powering the Future: A Critical Review of Research Progress in Enhancing Stability of High‐Efficiency Organic Solar Cells

“…Reproduced with permission. [ 129 ] Copyright 2023, Wiley‐VCH. d) Schematic diagram of adhesion enhancement with SEBS.…”

“…introduced the 2PACz layer between the PEDOT:PSS layer and the active layer to improve the stability of the device. [ 129 ] The results showed that 2PACz could chemically interact with PEDOT:PSS to achieve closer contact between the interfaces ( Figure 11c). Also, 2PACz can reduce the photocurrent loss caused by nongeminate recombination by inhibiting the formation of an intermixed p ‐doped PSS − ion‐rich region between BHJ/PEDOT:PSS contact interface.…”

“…c) Schematic illustration of the film structure in PEDOT:PSS/2PACz. Reproduced with permission [129]. Copyright 2023, Wiley-VCH.…”

Structure Influence of Amine‐Containing Additives on the Solution State and Out‐of‐Plane Conductivity of PEDOT:PSS for Efficient Organic Solar Cells

“…[8] While the secondary dopants are often introduced for busting the conductivity, therefore the processing additives or aftertreatments have been also explored for optimizing the nanostructure of the PEDOT:PSS thin films. [9][10][11] The thin film nanostructure is often focused for modification because the high solubility of PSS allows for the excess PSS remaining in solution while the PEDOT:PSS material aggregates in clusters, and the excess PSS molecules coated on the top of these clusters form an insulating barriers in a core-shell structure. For this reason, acid and polar solvents have been explored for removing excess PSS through soaking or rinsing processes, which results in increased conductivity and tuned energy levels.…”

Recent Advance in Solution‐Processed Hole Transporting Materials for Organic Solar Cells

“…Only the conducting polymer PEDOT:PSS and the transition metal oxide (TMO) MoO 3 have been widely used as HTLs for modifying anodes, and the best photovoltaic efficiencies in OSCs are obtained by utilizing the PE-DOT:PSS and MoO 3 HTLs. [12][13][14][15] However, the strong acidity of PEDOT:PSS severely degrades device stabilities. And the preparation of MoO 3 through energy-consuming vacuum evaporation certainly limits its use in the large-scale manufacturing.…”