Plasma induced degradation and surface electronic structure modification of Poly(3-hexylthiophene) films

Plasma treatment is an environmentally friendly solution for modifying or nanostructuring the surface of several materials including photoactive polymers. The detailed characterization of the effect of plasma treatment on chemical and optoelectronic properties of photoactive polymers is, therefore, of specific interest. Herein, the effect of the exposure of poly(3-hexylthiophene) (P3HT) thin films to plasma created in three different gases (oxygen, argon and hydrogen) was studied. A range of spectroscopic techniques, such as x-ray (XPS) and ultraviolet (UPS) photoelectron spectroscopy in conjunction with UV–vis absorption, Fourier transform infrared (FTIR) and photoluminescence (PL) spectroscopies, are employed to quantify the extent of chemical modification occurring in each particular case. It is shown that oxygen plasma treatment leads to the disruption of the π-conjugation via the direct oxidation of the sulfur atom of the thiophene ring while the aliphatic side chain remains nearly unaffected. An oxidation mechanism is proposed according to which the sulfur atom of the thiophene ring is oxidized into sulfoxides and sulfones, which subsequently degraded into sulfonates or sulfonic acids in a relatively small degree. For argon and hydrogen plasma treatments some oxidation products are detected only at the polymer surface. In all cases the polymer surface Fermi level is shifted closer to the highest occupied molecular orbital (HOMO) energy after plasma treatment indicating p-type doping arising from surface oxidation.</p

Surface Modification of ZnO Layers via Hydrogen Plasma Treatment for Efficient Inverted Polymer Solar Cells

Modifications of the ZnO electron extraction layer with low-pressure H plasma treatment increased the efficiency of inverted polymer solar cells (PSCs) based on four different photoactive blends, namely, poly­(3-hexylthiophene):[6,6]-phenyl C₇₁ butyric acid methyl ester (P3HT:PC₇₁BM), P3HT:1′,1″,4′,4″-tetrahydro-di­[1,4]­methano­naphthaleno-[5,6]­ullerene-C₆₀ (P3HT:IC₆₀BA), poly­[(9-(1-octylnonyl)-9H-carbazole-2,7-diyl)-2,5-thio­phenediyl-2,1,3-benzo­thiadiazole-4,7-diyl-2,5-thio­phenediyl]:PC₇₁BM (PCDTBT:PC₇₁BM), and (poly­[[4,8-bis­[(2-ethyl­hexyl)­oxy]­benzo­[1,2-<i>b</i>:4,5-<i>b</i>′]­dithio­phene-2,6-diyl]­[3-fluoro-2-(2-ethyl­hexy)­carbonyl]­thieno­[3,4-<i>b</i>]­thio­phenediyl]]):PC₇₁BM (PTB7:PC₇₁BM), irrespective of the donor:acceptor combination in the photoactive blend. The drastic improvement in device efficiency is dominantly attributable to the reduction in the work function of ZnO followed by a decreased energy barrier for electron extraction from fullerene acceptor. In addition, reduced recombination losses and improved nanomorphology of the photoactive blend in the devices with the H plasma treated ZnO layer were observed, whereas exciton dissociation also improved with hydrogen treatment. As a result, the inverted PSC consisting of the P3HT:PC₇₁BM blend exhibited a high power conversion efficiency (PCE) of 4.4%, the one consisting of the P3HT:IC₆₀BA blend exhibited a PCE of 6.6%, and our champion devices with the PCDTBT:PC₇₁BM and PTB7:PC₇₁BM blends reached high PCEs of 7.4 and 8.0%, respectively

Low Work Function Lacunary Polyoxometalates as Electron Transport Interlayers for Inverted Polymer Solar Cells of Improved Efficiency and Stability

From Crossref via Jisc Publications RouterHistory: epub 2017-06-28, issued 2017-06-28, ppub 2017-07-12Funder: General Secretariat for Research and Technology; FundRef: 10.13039/501100003448Funder: European Regional Development Fund; FundRef: 10.13039/501100008530Funder: European Social Fund; FundRef: 10.13039/50110000489