Understanding the synergistic effect of mixed solvent annealing on perovskite film formation

Morphology control of perovskite films is of critical importance for high-performance photovoltaic devices. Although solvent vapor annealing(SVA) treatment has been widely used to improve the film quality efficiently, the detailed mechanism of film growth is still under construction, and there is still no consensus on the selection of solvents and volume for further optimization. Here, a series of solvents(DMF, DMSO, mixed DMF/DMSO) were opted for exploring their impact on fundamental structural and physical properties of perovskite films and the performance of corresponding devices. Mixed solvent SVA treatment resulted in unique benefits that integrated the advantages of each solvent, generating a champion device efficiency of 19.76% with improved humidity and thermal stability. The crystallization mechanism was constructed by conducting grazing-incidence wide-angle x-ray diffraction(GIWAXS) characterizations, showing that dissolution and recrystallization dominated the film formation. A proper choice of solvent and its volume balancing the two processes thus afforded the desired perovskite film. This study reveals the underlying process of film formation, paving the way to producing energy-harvesting materials in a controlled manner towards energy-efficient and stable perovskite-based devices.

Reveal the growth mechanism in perovskite films via weakly coordinating solvent annealing

In this study, we investigated the nucleation mechanism of perovskite films by employing isopropanol(IPA), a weakly coordinating solvent, to anneal both PbI2 and CH3 NH3 PbI3 in the sequential deposition and CsPbI3 in the one-step deposition. IPA solvent annealing(IPA SA) of PbI2 films was carried out at different temperatures. The grain size,compactness, roughness and morphology of PbI2 and CH3 NH3 PbI3 films were seriously affected by annealing methods. Similarly, weakly coordinating solvent annealing process was also employed to anneal all inorganic CsPbI3 perovskite in a one-step method. A continuous and dense CsPbI3 film with uniform grain size was obtained. We recognized that weakly coordinating solvent annealing for perovskite could regulate the dissolution-recrystallization process via controlling the volume of residual solvent in perovskite intermediate films. The power conversion efficiency(PCE) of conventional CH3 NH3 PbI3 perovskite solar cells(PSCs)reached 17.4% and that of CsPbI3 PSCs reached 2.5% based on this sequential IPA SA process.

Polymersome formation by solvent annealing-induced structural reengineering under 3D soft confinement

A solvent annealing-induced structural reengineering approach is exploited to fabricate polymersomes from block copolymers that are hard to form vesicles through the traditional solution self-assembly route.More specifically,polystyrene-b-poly(4-vinyl pyridine)(PS-b-P4VP)particles with sphere-within-sphere structure(SS particles)are prepared by three-dimensional(3D)soft-confined assembly through emulsion-solvent evaporation,followed by 3D soft-confined solvent annealing upon the SS particles in aqueous dispersions for structural engineering.A water-miscible solvent(e.g.,THF)is employed for annealing,which results in dramatic transitions of the assemblies,e.g.,from SS particles to polymersomes.This approach works for PS-b-P4VP in a wide range of block ratios.Moreover,this method enables effective encapsulation/loading of cargoes such as fluorescent dyes and metal nanoparticles,which offers a new route to prepare polymersomes that could be applied for cargo release,diagnostic imaging,and nanoreactor,etc.

Effects of Thermal Annealing on the Solvent Additive P3HT PC61BM Bulk Heterojunction Solar Cells

Effects of thermal annealing on the optical, electrical and structural properties of 3 vol% 1,8-diiodoctane added P3HT：PC61BM active layers are investigated, concerning the performance of the bulk heterojunction polymer so- lar cells by changing the heat temperature. The structure information of the active layer is analyzed by using the grazing incidence wide angle scattering diffraction combined with the optical microscope, light absorption, pho- toluminescence and the external quantum efficiency spectra. The relationship between the detail of morphology and the optical, electrical properties is investigated.

Effect of dual annealing upon photovoltaic properties of polymer solar cells based on poly(3-hexylthiophene)

A dual annealing method comprised of toluene vapor treatment and post thermal annealing was employed to fabricate polymer solar cells （PSCs） based on poly（3-hexylthiophene） （P3HT） and [ 6,6 J-phenyl-C61-butyric acid methyl ester （PCBM） film. It is found that the P3HT crystallinity and chain ordering can be dramatically enhanced by this annealing process as compared with the films treated merely with solvent vapor annealing, which is verified by a higher X-ray diffraction intensity peak and clearly visible fibrillar crystalline domains of P3HT. The result suggests that a favorable e- quilibrium condition was established by dual annealing in the morphology reorganization. Due to the morphological improvement of active layer, the dually annealed PSCs show better overall perform- ances, with a mean power conversion efficiency of 4. 06% and an increase in each electrical parame- ter, than any solely annealed ones.

Self-assembly of Blended PS-b-P2VP Block Copolymers

Directed Self-Assembly(DSA)of block copolymers(BCPs)is a promising technique for sub-10 nm nanofabrication,which is highly compatible with conventional lithography.DSA relies on the microphase separation of block copolymers to form nanostructures of different morphologies.The pitch size of the obtained nanostructure depends largely on the intrinsic properties of BCPs and is usually fixed when BCPs are produced.One effective way of tuning the pitch size of BCPs is by blending BCPs of different molecular weight.In this paper,we have demonstrated the pitch tuning capability by blending the triblock poly(2-vinyl pyridine-bpolystyrene-b-poly 2-vinyl)pyridine(P2VP-b-PS-b-P2VP)with another triblock P2VP-b-PS-b-P2VP or diblock copolymer(PS-b-P2VP)at various volume ratios by solvent annealing.The nanopatterns of blended BCPs after sequential infiltration synthesis(SIS)and plasma etching process,were characterized by scanning electron microscopy.It’s observed that the blended BCPs can form highly ordered lamellar nanostructures of different pitch sizes at different blending ratios.The method of blending BCPs of varying molecular weights greatly extends the functionality of existing BCPs,with the capability of fine-tuning nanopatterning pitch at nanometer resolution.

Solvent Vapor Annealing Induced Polymorphic Transformation of Polybutene-1

Solvent annealing is a facile method for changing the aggregated microstructure and physical properties of polymer materials. In this paper, we addressed the effects of solvent vapor annealing, including chloroform and water vapor, on the polymorphic transformation in both hot-pressed film and electrospun nonwoven of isotactic polybutene-1 （PB-1） by means of in situ Fourier transform infrared spectroscopy （FTIR）. The pretty rapid transition rate caused by the increased motion of molecular chains under chloroform vapor is associated with a lowest crystallinity. Also, a decreased crystallinity with the crystal transition occurred in electrospun nonwovens resulting from the relaxation of the stretched molecular chains into amorphous state rather than realignment into crystal form I predominating the crystal transition process.

Synergistic Effects of External Electric Field and Solvent Vapor Annealing with Different Polarities to Enhance β-Phase and Carrier Mobility of the Poly(9,9-dioctylfluorene)Films

In this work,the synergistice efects of external electric field(EEF)and solvent vapor annealing to enhanceβ-phase and carrier mobility of poly(9,9-dioctylfuorene)(PFO)films were investigated.It is found that EEF can promote the PFOβ-phase conformation transition and orientate the PFO chains along the EEF direction with the as-sistance of polar solvent vapor annealing.PFO chain orderness is closely related to the solvent polarity.In particular,the B-phase content in the annealed film of strong polar chloroform vapor increases from 18.7%to 34.9%after EEF treatment.Meanwhile a characteristic needle-like crystal is formed in the flm,as a result,the hole mobility is en-hanced by an order of magnitude.The mechanism can be attributed to the fast polarization of solvent dipole under the action of EEF,thus forming a driving force that greatly facilitates the orientation of PFO dipole unit.Research also reveals that EEF driving of the PFO chains does not occur with an insoluble solvent vapor since the solvent molecules cannot swell the film,thus there is insufficient free volume for PFO chains to adjust their conformation.This research enriches the understanding of the relationship between solvent vapor annealing and EEF in orientation polymers,and this method is simple and controlled,and capable of integrating into large-area thin film process,which provides new insights to manufacture low-cost and highly ordered polymer films,and is of great significance to enhance carrier mobility and efficiency of photoelectric devices based on polymer condensed matter physics.

Nanopattern Transformation ofABC Triblock Copolymer Thin Films Induced by Strong Solvent Selectivity and Annealing

Nanopattem transformation behaviors of polyisoprene-block-polystyrene-block-poly（2-vinylpyridine） （PI-b-PS-b-P2VP） asymmetric ABC triblock copolymer were investigated systematically with various control para- meters, including different solvents for polymer solution and annealing conditions in this paper. Ordered nanopattern of PI-b-PS-b-P2VP with hexagonal cylinders could be obtained when PI-b-PS-b-P2VP toluene solution was spin-coated on silicon substrate followed by toluene vapor annealing process. When the film with hexagonal and cylindrical nanopattern was exposed to saturated toluene vapor, the order-order transition of cylindrical nanopattern to parallel nanopattern was observed due to the strong selectivity of toluene to PS and PI blocks. Furthermore, fingerprint nanopattern could also be obtained by solvent annealing in tetrahydrofuran vapor. The nanopattern trans- formation was due to different selectivity of solvents and incompatibilities of the three blocks of PI-b-PS-b-P2VP under various solvent annealing conditions.

Morphology optimization of photoactive layers in organic solar cells

Organic solar cells(OSCs)have unique advantages of light weight,low-cost solution processing,and capability to be fabricated into flexible and semitransparent devices,which are widely recognized as a promising photovoltaic technology.Photoactive layers of the OSCs are composed of a blend of a p-type organic semiconductor as a donor(D)and an n-type organic semiconductor as acceptor(A).The morphology of the active layer with D/A nano-scaled aggregation and face-onπconjugated packing,and D/A interpenetrating network is crucial for achieving high photovoltaic performance of the OSCs.Therefore,great efforts have been devoted to control and optimize morphology of the active layers.This perspective focuses on the morphological control by solvent/solid processing additives and the morphology optimization by postdeposition treatment with thermal annealing and/or solvent vapor annealing,which have been extensively adopted and exhibit promising positive effect in optimizing the morphology.Representative examples are given and discussed to understand the foundation of the postdeposition treatments on tuning the morphology.Insights into the role of the postdeposition treatments and additive treatments on the morphology optimization will be beneficial to further improvement in morphology optimization for practical organic photovoltaic application.

A Facile Method to Form a Densely Grafted PEO-b-P4VP Brush on Gold Surface

Here we report a facile method for the preparation of a PEO113-b-P4VP93 brush on gold surface with a grafting density as high as 1.32 chains/nm2; the P4VP blocks were physically adsorbed on gold surface forming an inner layer while the PEO blocks stretched towards the solution forming PEO brush. PEOl13-b-P4VPq3 micelles with P4VP core and PEO shell formed in methanol/water mixed solvents were used as the precursor. By adsorbing PEOII3-b-P4VP93 micelles from pure water, in which the density of the micelles is the largest, maximum amount of the micelles was adsorbed onto gold surface, and the adsorbed micelles existed as individual domains on the surface To prepare the polymer brush with a density as high as possible, we annealed the adsorbed micelles by metha- nol/water mixed solvent at the volume fraction of methanol （VF） of 20%, which was the proper proportion at which the core-forming P4VP chains began to be flexible but the integrity of the micelles was remained. At this volume fraction, almost all the adsorbed micelles originally existing as individual domains were transformed into a dense polymer brush.

18.01%Efficiency organic solar cell and 2.53%light utilization efficiency semitransparent organic solar cell enabled by optimizing PM6:Y6 active layer morphology

Optimizing the photoactive layer morphology is a simple,promising way to improve the power conversion efficiencies(PCEs)of organic solar cells(OSCs).Here,we compared different post-processing treatments on PM6:Y6 blend films and relevant effects on device performances,including as-cast,thermal annealing and solvent annealing.This solvent annealing processes can effectively improve the vertical distribution and aggregation of polymer donors and small molecule acceptors,then optimize the active layer film morphology,ultimately elevating PCE.Thus,one of champion efficiencies of 18.01%was achieved based on the PM6:Y6 binary OSCs.In addition,a relatively high light utilization efficiency(2.53%)was achieved when a transparent electrode made of Cu(1 nm)and Ag(15 nm)was utilized to fabricate a semitransparent OSC with a remarkable PCE of 13.07%and 19.33%average visible-light transmittance.These results demonstrated that carefully optimizing morphology of active layer is conducive to achieving a high-performance OSC.