Effect of aggregation behavior and phenolic hydroxyl group content on the performance of lignosulfonate doped PEDOT as a hole extraction layer in polymer solar cells

Abstract

†Electronic Supplementary Information (ESI) available: [the results including SEM images of various block-like self-assemblies from LS and ALS; DLS measurement of LS solution and ALS solution in H2O/EtOH (v/v, 1/3); Proposed schematic for the polymerization of EDOT in the presence of LS and ALS; UV absorption spectra of PEDOT:LS and PEDOT:ALS aqueous dispersion]. SeeUsing lignosulfonate (LS) and alkyl chain-coupled lignosulfonate-based polymer (ALS) as raw material, the aggregation behavior of LS and ALS was investigated, which all showed unique aggregation behavior to form block-like self-assembly for the first time. The aggregation behavior and mechanism of LS and ALS was investigated by SEM, TEM and DLS. The block-like aggregates prepared from ALS (micron size) were larger than that of LS (nano size). The unique aggregates were also further confirmed by XPS, meanwhile, SAXS was applied to explore the regular intrinsic characteristics of the blocklike aggregates. Inspired by the aggregation behavior of LS and ALS, the electron transfer properties of LS and ALS were also studied including electrochemical property and hole mobility measurement. The oxidation peaks at 1.2 V and 1.4 V were observed at the LS and ALS modified electrode, respectively. We studied hole transport property of LS and ALS with space-charge-limited current method (SCLC). The average hole mobilities of 2.95×10 -6 cm 2 V -1 s -1 and 3.18×10 -7 cm 2 V -1 s -1 were estimated for LS and ALS, respectively. The above results indicated that LS and ALS are potential water soluble polymeric p-type semiconductors, and the electron transfer property of LS is better than that of ALS. Based on the unique aggregation behavior and hole mobility above which will facilitate charge transport, water soluble PEDOT:LS and PEDOT:ALS were prepared and applied as hole extraction layer (HEL) in polymer solar cells. The PCE decreased with the decrease of phenolic hydroxyl group content (-OH), which suggested that -OH is important for the property of PCE. The application properties were consistent with the results of aggregation behavior and electron transfer properties. The power conversion efficiency (PCE) of 5.19% from PEDOT:LS-1:1 as HTL was achieved with device structure of ITO/HEL/PTB7:PC71BM/Al in our study. Our results showed the phenolic hydroxyl group content and conjugation structure of amorphous LS contribute its promising potential as dopant of semiconductors, such as PEDOT in organic electronics. Our result provides a novel perspective for the design of dopant for semiconductive polymer.All in one word, phenolic hydroxyl group of polymer will provide hole transport capability due to its oxidation during device orperation.

“Waste to Wealth”: Lignin as a Renewable Building Block for Energy Harvesting/Storage and Environmental Remediation

“…(A) Lignin and its derivatives in DSSCs: (i) modified lignophenols as photosensitizer, and (ii) lignin‐derived carbon electrode. (B) Lignin/conductive polymer as a HTL in perovskite solar cells: (i) device architecture, (ii) energy‐level diagram, and (iii) proposed electron‐transfer process of lignin‐based HTL: PEDOT:LS (up) and PEDOT:ALS (down) . (iii) Reproduced with permission .…”

Lignin-Based Composite Materials for Photocatalysis and Photovoltaics

“…Block-like aggregation behavior was more dominant in ASL compared to SL due to cross-linked alkyl chain polymerization in SL. Based on the aggregation behavior and electron transport characteristics of the SL and ASL, the materials have been applied as dopants to improve the conductivity of PEDOT [ 109 ]. The power conversion efficiency of polymer solar cell also depends on the aggregation behavior of the dopants that is ultimately affected by the hydroxyl group content [ 105 , 109 ].…”

“…The results of the study also showed that hydroxyl group content is directly related to the hole mobility and PCE, whereas increase in hydroxyl group increased hole transport ability and PCEs and vice versa. Furthermore, the high pH of SL and ASL is an advantage of the conductive polymers over conventional dopant PSS that will prevent corrosion of ITO layers [ 109 ].…”

Investigation of the hole transport characterization and mechanisms in co-evaporated organic semiconductor mixtures

“…So far the charge carrier transport characteristics in organic semiconductors have been usually analyzed by several techniques, such as time of ight (TOF), 9,10 transient electroluminescence (TEL), 11,12 space charge limited current (SCLC) [13][14][15] and admittance spectroscopy (AS). [16][17][18][19][20][21] In these techniques, notably, AS has been shown to be a feasible and powerful tool to explore the charge carrier transport kinetics and relaxation processes and involved in optoelectronic devices.…”