Nafion-Modified PEDOT:PSS as a Transparent Hole-Transporting Layer for High-Performance Crystalline-Si/Organic Heterojunction Solar Cells with Improved Light Soaking Stability

Abstract

We demonstrate the chemistry of amphiphilic perfluorosulfonic copolymer Nafion-coated conductive poly(3,4-ethyelenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and its effect on the photovoltaic performance of PEDOT:PSS/crystalline Si (c-Si) heterojunction solar cells. The highly hydrophilic sulfonate group of insulating, chemically stable Nafion interacts with PSS in PEDOT:PSS, which reduce the Coulombic interaction between PEDOT and PSS. The highly hydrophobic fluorocarbon backbone of Nafion favorably interacts with hydrophobic PEDOT of PEDOT:PSS. These factors give rise to the extension of π-conjugation of PEDOT chains. Silver paste used as a top grid electrode diffused into the Nafion layer and contacted with underneath Nafion-modified PEDOT:PSS layer. As a consequent, solution-processed Nafion-coated PEDOT:PSS/c-Si heterojunction solar cells exhibited a higher power conversion efficiency of 14.0% with better stability for light soaking rather than that of the pristine PEDOT:PSS/c-Si device by adjusting the layer thickness of Nafion. These findings originate from the chemical stability of hydrophobic fluorocarbon backbone of Nafion, diffusivity of silver paste into Nafion and contact with PEDOT:PSS, and Nafion as an antireflection layer.

Highly Conductive and Wettable PEDOT:PSS for Simple and Efficient Organic/c‐Si Planar Heterojunction Solar Cells

“…These results suggest that DMSO solvent induces a rearrangement of the PEDOT chains, from coil‐like benzoid to a more fibrillary‐like quinoid structure. In the fibrillary‐like quinoid structure conformation, charges could be more delocalized in the PEDOT:PSS film, which increase the number of the carrier concentration duo to the delocalization of π‐electrons in the linear backbone of the structure . This is consistent with Hall measurement.…”

“…It shows that as the DMSO doping increases, the total peak of the starching vibration of C a C b band weakly moves to a lower frequency, and the position peak of the benzoid (D: 1457 cm −1 ) shows a peak collapse trend. This means that the content of benzoid structural components gradually decreases . Figure b shows normalized Raman spectra data for Triton X‐100‐doped PEDOT:PSS films (5 wt% DMSO doped) with or without DMF washing treatment.…”

“…To investigate structural variations in the PEDOT:PSS films, Raman spectra of the PEDOT:PSS films were measured. Raman spectroscopy is a powerful tool for studying the molecular‐level changes in a polymer . Figure S2, Supporting Information, shows micro‐Raman spectra of c‐Si substrate and pristine PEDOT:PSS (PH‐1000) film on c‐Si substrate.…”

“…Raman spectroscopy is a powerful tool for studying the molecular-level changes in a polymer. [33] Figure S2, Supporting Information, shows micro-Raman spectra of c-Si substrate and pristine PEDOT:PSS (PH-1000) film on c-Si substrate. The positions of bands typical for PEDOT:PSS are shown in Table S3, Supporting Information.…”

“…[34] The deconvolution of this vibration peak gives three peaks at 1435, 1457, and 1405 cm À1 , which correspond to quinoid symmetric C a -C b (-O) stretching, benzoid symmetric C a ═C b (-O) stretching, and an intermediate state absorption mode, respectively. [33,35] Figure 2a shows normalized Raman spectra data for DMSO-doped PEDOT:PSS films on c-Si at around 1430 cm À1 . It shows that as the DMSO doping increases, the total peak of the starching vibration of C a ═C b band weakly moves to a lower frequency, and the position peak of the benzoid (D: 1457 cm À1 ) shows a peak collapse trend.…”