A futuristic strategy to influence the solar cell performance using fixed and mobile dopants incorporated sulfonated polyaniline based buffer layer
Date
2015
Authors
Sai Anand, G.
Gopalan, A.I.
Lee, K.P.
Venkatesan, S.
Kang, B.H.
Lee, S.W.
Lee, J.S.
Qiao, Q.
Kwon, D.H.
Kang, S.W.
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Journal article
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Solar Energy Materials and Solar Cells, 2015; 141(10):275-290
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Abstract
In this work, we hypothesized and demonstrated a new strategy to tune/modulate the electrochemical, microstructural and opto-electronic properties based on the manipulation of the intentionally included external dopant ion (X-) within the sulfonated polyaniline (SPANs). Through our new strategy, we developed a different type of SPANs comprising of internal (fixed) and external (mobile) dopant. The X- included SPANs were prepared through a sequential doping, dedoping and redoping processes and designated as SPAN-R (X-) (where X- is the anion of toluene sulfonic acid (TSA) or camphor sulfonic acid (CSA) or napthalene sulfonic acid (NSA)) by modifying the structure of 4-aminodiphenylamine-2-sulfonic acid with additional polyaniline chains to accommodate X-. SPAN-R(X-) polymers were characterized by cyclic voltammetry, UV-visible spectroscopy, attenuated total reflectance-Fourier transform infrared spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Atomic force microscopy to elucidate the influence of X- on the electrical, optoelectronic, microstructural properties and surface properties on the performance characteristics of polymer solar cells (PSCs) fabricated with SPAN-R(X-) as a buffer layer. The electrochemical band gap, degree of doping (DD), electrical conductivity and degree of crystallinity (CD) were evaluated and correlated to understand the influence of X- on them. The power conversion efficiency (PCE) of PSCs featuring SPAN-R(TSA(-)) as a buffer layer showed a similar to 3.2 times improvement in the overall PCE, compared with the PSCs having pristine SPAN (not containing X-) as a buffer layer and is higher than that of SPAN-R(CSA(-)) and SPAN-R(NSA(-)) based devices. The superior photovoltaic (PV) characteristics observed for SPAN-R(TSA(-)) is due to the synergistic contributions from appropriate energy-level/work function alignment, higher conductivity, higher DD and induced molecular order with the photoactive layer. Importantly, PSCs with SPAN-R(X-) buffer layer processed at low temperature (30 degrees C) (without thermal treatment) exhibited improved PV characteristics and better air-stability as compared to the device having poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) (thermally annealed at 150 degrees C) as buffer layer. As buffer layers, SPAN-R(X-) polymers, containing fixed and mobile dopants, are most attractive because of low temperature processability and improved solar cell performance. (C) 2015 Elsevier B.V. All rights reserved.
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Copyright 2015 Elsevier