The influence of three different solvents and a solvent additive on the morphology and photovoltaic performance of bulk heterojunction films made of the copolymer based on thieno[3,4-b]thiophene-alt-benzodithiophene unit PTB7-F40 blended with [6,6]-phenyl-C71-butyric acid methyl ester (PCBM) is investigated. Optical microscopy and atomic force microscopy are combined with X-ray reflectivity and grazing incidence small and wide-angle X-ray scattering (GISAXS and GIWAXS, respectively), enabling the characterization of the morphology of the whole photoactive film. The detailed study reveals that different length scales of PCBM clusters are observed using different solvents, while adding a solvent additive results in the PCBM clusters being selectively dissolved. Vertical and lateral phase separation occurs during spin coating and depends on the solvent used. A hierarchical morphology is detected within the bulk film through GISAXS measurements. Furthermore, GIWAXS shows that a rather amorphous film with low crystallinity was probed, which substantiates that high crystallinity is not necessarily required for high performance organic solar cells. Different models for the morphology are proposed through the combination of all the findings and correlated with the corresponding device properties. Consequently, the solvent-induced different device performance is mainly ascribed to the varied lateral structure sizes, whereas the highest device performance is a result of the smallest average multilength scale lateral structure sizes with the smallest length scale matching the exciton diffusion length.

The degradation of poly(3-hexylthiophene) (P3HT)− titania-based solid-state dye-sensitized solar cells (ssDSSCs) is studied to better understand device aging mechanisms. The correlation of temporal evolution between P3HT crystallite structures and device performance is discussed for the first time using in situ measurements. For comparison, two types of mesoporous titania photoanodes with different pore sizes are prepared. Grazing incidence wide-angle X-ray scattering is used in situ under continuous solar illumination to obtain information about the impact of pore size on P3HT crystalline order and on temporal evolution of the P3HT crystallites. The development of the photovoltaic characteristics is explored in parallel. The lattice constants, crystal sizes, and volume fraction of crystalline P3HT in the large-pore active layer remain stable over 30 min, while the volume fraction of crystalline P3HT decreases in the small-pore active layer. Thus, the pore size of titania photoanodes is important for the stability of P3HT−titania-based ssDSSCs.

From a morphological perspective, the understanding of the influence of the [6,6]-phenyl C71-butyric acid methyl ester (PC71BM) content on the morphology of the active layer is not complete in organic solar cells (OSCs) with bulk heterojunction (BHJ) configuration based on the low-bandgap polymer poly­[4,8-bis­(5-(2-ethylhexyl)­thiophen-2-yl)­benzo­[1,2-b;4,5-b′]­dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno­[3,4-b]­thiophene-)-2-carboxylate-2-6-diyl] (PTB7-Th). In this work, we obtain the highest power conversion efficiency (PCE) of 10.5% for BHJ organic solar cells (OSCs) with a PTB7-Th/PC71BM weight ratio of 1:1.5. To understand the differences in PCEs caused by the PC71BM content, we investigate the morphology of PTB7-Th/PC71BM blend films in detail by determining the domain sizes, the polymer crystal structure, optical properties, and vertical composition as a function of the PC71BM concentration. The surface morphology is examined with atomic force microscopy, and the inner film morphology is probed with grazing incidence small-angle X-ray scattering. The PTB7-Th crystal structure is characterized with grazing incidence wide-angle X-ray scattering and UV/vis spectroscopy. X-ray reflectivity is employed to yield information about the film vertical composition. The results show that in PTB7-Th/PC71BM blend films, the increase of PC71BM content leads to an enhanced microphase separation and a decreased polymer crystallinity. Moreover, a high PC71BM concentration is found to decrease the polymer domain sizes and crystal sizes and to promote polymer conjugation length and formation of fullerene-rich and/or polymer-rich layers. The differences in photovoltaic performance are well explained by these findings.

Novel hydrogen evolution system based on hybrid nanogel films are successfully prepared with capabilities of spontaneous moisture collection and high light harvesting. Hybrid nanogels are synthesized by homogenously dispersing graphitic...

Morphology regulation and electronic structure modulation are very important means to improve the photocatalytic H2 evolution of metal-free graphitic carbon nitride (g-C3N4) photocatalyst. Herein, we constructed a multiple ordered porous...

The simultaneous and efficient removal of oleophilic and hydrophilic stains from polyurethane (PU) is realized by combining the easy-cleaning from the hydrophilic thermoresponsive hydrogel coating containing acrylamide (AAm), gum arabic (GA), and (ethylene glycol) methyl ether methacrylate (OEGMA300) P­(GA/AAm/OEGMA300) and the self-cleaning from the embedded nonmetallic photocatalyst g-C3N4. Due to the existence of strong hydrogen bonds between the hydroxyl groups in the hybrid hydrogel coating and the hydroxyl/carboxyl groups in the plasma-treated PU, the hybrid hydrogel coating is very stable on PU. Simultaneously, the acrylamide network in the hybrid hydrogel coating enhances its mechanical strength. Because the transition temperature of OEGMA300 is well above the room temperature, the cross-linked coating remains hydrophilic in ambient conditions. Thus, oleophilic stains, such as oil and grease, can be easily removed from the coating surface. In addition, the embedded photocatalyst g-C3N4 in the hybrid hydrogel coating introduces the extra capability of decomposing organic compounds under sunshine, which favors the removal of hydrophilic stains such as dyes and wines. After sunlight illumination and simply rinsing with water, both hydrophilic and oleophilic stains can be easily removed. Moreover, this joint cleaning performance can work for a long time. Even after four consecutive cycles, both the easy-cleaning to oleophilic stains by the hydrophilic hydrogel surface and self-cleaning to the hydrophilic stains by the embedded g-C3N4 remain unchanged.

Metal-free graphitic carbon nitride (g-C3N4) has become one of the most up-and-coming photocatalyst candidates for the hydrogen evolution reaction. However, the improvement in photocatalytic property is strongly suppressed by the limited active reaction sites due to the bulk microstructure of g-C3N4. On this basis, we exploit a moderate and economical approach to prepare an ordered and one-dimensionally ultralong carbon nitride nanotube (CN-NT) via the in-air chemical vapor deposition (CVD) with SiO2 nanofiber templates synthesized by electrostatic spinning. Due to the uniform size, fluffiness, and easy removal, SiO2 nanofiber templates are conducive to prepare ordered and tubular CN-NT. The obtained CN-NT sample exhibits an excellent photocatalytic hydrogen evolution rate (HER) of 4605.2 μmol·h–1·g–1 under visible light, which is 33.4 times higher than that of the original bulk g-C3N4. The apparent quantum efficiency reaches 6.49% at 420 nm. The enhancement in the photocatalytic activity is ascribed to the increased specific surface area, faster electron transfer pathway, advanced light absorption ability, and furthermore the lower recombination rate of photogenerated electrons.

The durability of titania and titania composite films under mechanical stress is studied and modeled with respect to the morphology.