Optimization of solvent swelling for efficient organic solar cells via sequential deposition

Compared to bulk heterojunction(BHJ)organic solar cells(OSCs)prepared by the blend casting in“one step process”,sequential deposition(SD)processed OSCs can realize an ideal profile of vertical component distribution due to the swelling of polymer films.Herein,we did trials on several kinds of second solvents for swelling the polymer layer,and investigated the packing structure and morphology of the swollen films and the performance of the resulting devices.We found that an optimized morphology can be achieved by solvent swelling while using orthodichlorobenzene(o-DCB)as the second layer processing-solvent,with polymer donor PffBT-3 as bottom layer,PC71BM as top layer and bicontinuous networks in the middle.Such solvent swelling process also makes the SD method exempt from thermal annealing treatment.The device based on SD yields a power conversion effi-ciency(PCE)up to 8.7%without any post-treatment,outperforming those from the devices based on SD using other solvents and that(7.06%)from BHJ device,respectively.We also extended the use of this approach to allpolymer blend system,and successfully improved the efficiency from 4.72%(chloroform)to 9.35%(o-DCB),which is among the highest PCEs in all-polymer-based OSCs fabricated with SD method.The results demonstrate that the swelling of the polymer by the second layer solvent is a necessity for SD,paving the way towards additivefree high-performance OSCs.

Improving performance of direct coal liquefaction through swelling with solvent under the radiation of ultrasonic wave

Three kinds of lower rank bituminous coals from Yanzhou mine and Tengxian mine from Shandong Province were treated and hydrogenated in the study. The test re- sults show that the performance of hydrogenation liquefaction of the pretreated coals is improved markedly. Under the test condition of H2 initial pressure 8.2 MPa, addition of FeSO4·7H2O and S as catalyst, final reacting temperature 400 ℃ and reacting time 1.5 h, the oil yield of pretreated YZ1 coal is 69.76% compared with 62.53% of oil yield of un- treated YZ1. Seminally the oil yield of pretreated YZ2 coal is 55.43% compared with 20.88% of untreated YZ2 coal. The results of tests also prove that the improving degree of hydrogenation liquefaction of the pretreated coals is related with radiation duration when the radiation frequency and radiation power of ultrasonic wave are fixed.

Swelling Process of Thin Polymer Film Studied via in situ Spectroscopic Ellipsometry

The swelling process of thin polystyrene films in quantity was studied in this paper using the in situ spec- troscopic ellipsometry. We systematically investigated the influence of film thickness on the swelling process of thin polystyrene films. The results show that in the case of high Mw polystyrene（Mw=400000）, the curve of the swelling degree as a function of time discloses that the relaxation of the long polymer chains accompanies the diffusion of acetone molecules, The swelling process is via the Fickian relaxation mechanism. Both the values of the equilibrium swelling degree and the diffusion coefficient of acetone molecules in the polystyrene film decrease as the film thick- ness reduces under confinement. However, in the case of lowMw PS（Mw=4100）, the dewetting process is so fast be- fore the equilibrium of swelling that the whole swelling process cannot be observed.