Conjugated polymers are a promising candidate for large-area stretchable electronics because of their tunable electrical and mechanical properties, light weight, and low-cost solution processing. Significant research progress has been achieved in stretchable polymer electronics by synthesizing novel conjugated polymer materials and designing new device geometries. However, the inherent competition between high charge mobility and good mechanical compliance has long existed for conjugated polymer films. In this Perspective, we will provide an understanding of how to balance the electrical properties and mechanical properties from the point of view of multiple length scale microstructures of conjugated polymers. After a brief introduction of microstructure features, charge transport, and mechanical properties in thin films, we focus on how to design the percolation morphology with the aggregates, tie chains, and amorphous phase via controlling solution preaggregation and film-formation dynamics. Furthermore, the rational transfer of film morphology from small-area coating to large-area printing is discussed in terms of film uniformity and crystallization control. Finally, we summarize the challenges and opportunities in microstructure control of stretchable conjugated polymer films.

Even though the perovskite solar cell has been so popular for its skyrocketing power conversion efficiency, its further development is still roadblocked by its overall performance, in particular long-term stability, large-area fabrication and stable module efficiency. In essence, the soft component and ionic–electronic nature of metal halide perovskites usually chaperonage large number of anion vacancy defects that act as recombination centers to decrease both the photovoltaic efficiency and operational stability. Herein, we report a one-stone-for-two-birds strategy in which both anion-fixation and associated undercoordinated-Pb passivation are in situ achieved during crystallization by using a single amidino-based ligand, namely 3-amidinopyridine, for metal-halide perovskite to overcome above challenges. The resultant devices attain a power conversion efficiency as high as 25.3% (certified at 24.8%) with substantially improved stability. Moreover, the device without encapsulation retained 92% of its initial efficiency after 5000 h exposure in ambient and the device with encapsulation retained 95% of its initial efficiency after >500 h working at the maximum power point under continuous light irradiation in ambient. It is expected this one-stone-for-two-birds strategy will benefit large-area fabrication that desires for simplicity.

Two‐dimensional alternating cation (ACI)‐type perovskites self‐assemble in solution to form highly ordered periodic stacks with unique physical properties and improved optoelectronic devices. Tailoring composition and distribution of quantum wells (QWs) is of vital importance for the optoelectronic properties and stability, which, however, have been less reported in contrast to their Ruddlesden–Popper (RP) and Dion–Jacobson (DJ) counterparts. Herein, crystallization control via solvent engineering for ACI perovskite (GA)MA n Pb n I3n+1 ( = 5, GA = guanidinium, MA = methylammonium) that enables preferential QW distribution within the film and augments the crystallinity and smoothness of the films is proposed. It is found that such morphological improvements are further reflected in the optoelectronic properties, including enhanced charge carrier transport/extraction and suppressed nonradiative charge recombination. Thus, efficient and stable ACI perovskite solar cells with a power conversion efficiency (PCE) of 19.18%, standing the highest among all reported RP, DJ, and ACI ( ≤ 5) solar cells, are realized. Meanwhile, the device exhibits superior reproducibility and environmental stability. These findings highlight the importance of crystallization control and pave the way for the realization of high‐performance 2D perovskite solar cells.

High concentration of ascorbic acid (vitamin C) has been found in corneal epithelium of various species. However, the specific functions and mechanisms of ascorbic acid in the repair of corneal epithelium are not clear. In this study, it was found that ascorbic acid accelerates corneal epithelial wound healing in vivo in mouse. In addition, ascorbic acid enhanced the stemness of cultured mouse corneal epithelial stem/progenitor cells (TKE2) in vitro, as shown by elevated clone formation ability and increased expression of stemness markers (especially p63 and SOX2). The contribution of ascorbic acid on the stemness enhancement was not dependent on the promotion of Akt phosphorylation, as concluded by using Akt inhibitor, nor was the stemness found to be dependent on the regulation of oxidative stress, as seen by the use of two other antioxidants (GMEE and NAC). However, ascorbic acid was found to promote extracellular matrix (ECM) production, and by using two collagen synthesis inhibitors (AzC and CIS), the increased expression of p63 and SOX2 by ascorbic acid was decreased by around 50%, showing that the increased stemness by ascorbic acid can be attributed to its regulation of ECM components. Moreover, the expression of p63 and SOX2 was elevated when TKE2 cells were cultured on collagen I coated plates, a situation that mimics the in vivo situation as collagen I is the main component in the corneal stroma. This study shows direct therapeutic benefits of ascorbic acid on corneal epithelial wound healing and provides new insights into the mechanisms involved. Stem Cells Translational Medicine 2017;6:1356–1365

Conjugated polymers exhibit potential for the development of next-generation stretchable electronics. However, an understanding of molecular aggregation during solution processing and its influence on thin-film morphology is still underexplored. Here, the influences of molecular aggregation on the film morphology, phase purity and phase separation, and mechanical and electrical properties of a partially compatible blend of conjugated polymer poly(indacenodithiophene-co-benzothiadiazole) (IDTBT) and elastomer polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS) were systematically examined. When using high-boiling-point (b.p.) solvents, namely, toluene and chlorobenzene, large-scale liquid−liquid phase separation predominates IDTBT aggregation in blend films, leading to isolated IDTBT domains and, thus, poor electrical performance. In contrast, fast solvent evaporation from low-b.p. chloroform suppresses large-scale phase separation and enhances IDTBT aggregation via nanoconfinement effect. The nanoconfinement effect enables us to achieve a stretchable film with a low elastic modulus of 72 MPa, a respectable crack-onset strain of 326% (ca. 3−14 times larger than the neat IDTBT films), and a negligible loss of mobility (ca. 0.7 cm 2 V −1 s −1 ) at 100% strain. These results provide insight into molecular aggregation and thin-film morphology in conjugated polymer/elastomer blends for high-performance stretchable electronics.

optical absorption coefficient, [1] high carrier mobility, [2] low exciton binding energy, [3] long carrier diffusion length, [4] adjustable bandgap, [5] and low manufac turing cost. [6] To date, the certified photo electric conversion efficiency (PCE) for perovskite solar cells (PSCs) has reached 25.5%, [7] which makes PSCs a strong future competitor in the photovoltaic industry. FAPbI 3 has been widely used as the light absorber for singlejunction PSCs due to its narrower bandgap and higher Shockley-Queisser limit efficiency compared with MAPbI 3 . [8] However, the perovskite devices based on FAPbI 3 poly crystalline films face the problem of phase and environmental instability. [9] The black α phase easily transforms to the yellow δ phase, which destroys the optoelectronic properties. [10] The phase instabilities are accelerated by the poor quality of the perovskite polycrystalline film, which is closely correlated with the crystallization process. [11] At present, rapid crystallization by the mostused solution method with N,Ndimethylformamide (DMF) or dime thyl sulfoxide (DMSO) solvent will inevi tably lead to the formation of a solution-complex intermediate phase, such as FAI-PbI 2 -DMSO, in the perovskite crystalliza tion process. [12] However, the final product will not be pure and stable αFAPbI 3 after the process of hightemperature annealing With its power conversion efficiency surpassing those of all other thin-film solar cells only a few years after its invention, the perovskite solar cell has become a superstar. Controlling the intermediate phase of crystallization is a key to obtaining high-quality perovskite films. Herein, a single molecule additive, N,N-dimethylimidodicarbonimidic diamide hydroiodide (DIAI), is incorporated into the perovskite precursor to eliminate the influence of intermediate phases. By taking advantage of the interaction of DIAI and dimethyl sulfoxide (DMSO), the intermediate phase FAI-PbI 2 -DMSO complex is eliminated, and δ-FAPbI 3 is entirely converted to the desired α-FAPbI 3 during the crystallization step, resulting in enlarged grain size and improved crystalline quality. This is the first observation in the solution method that FAPbI 3 can be obtained without an intermediate phase for high-performance perovskite solar cells. Furthermore, DIAI is effective at passivating surface defects, resulting in reduced defect density, increased carrier lifetime, and improved device efficiency and stability. The champion device achieves an efficiency of 24.13%. Furthermore, the bare device without any encapsulation maintains 94.1% of its initial efficiency after ambient exposure over 1000h. This work contributes a strategy of synergistic crystallization and passivation to directly form α-FAPbI 3 from the precursor solution without the influence of intermediate impurities for high-performance perovskite applications.

New structural type of 2D AA′ n−1 M n X 3n+1 type halide perovskites stabilized by symmetric diammonium cations has attracted research attention recently due to the short interlayer distance and better charge-transport for high-performance solar cells (PSCs). However, the distribution control of quantum wells (QWs) and its influence on optoelectronic properties are largely underexplored. Here effective phase-alignment is reported through dynamical control of film formation to improve charge transfer between quantum wells (QWs) for 2D perovskite (BDA)(MA) n-1 Pb n I 3n+1 (BDA = 1,4-butanediamine, 〈n〉 = 4) film. The in situ optical spectra reveal a significantly prolonged crystallization window during the perovskite deposition via additive strategy. It is found that finer thickness gradient by n values in the direction orthogonal to the substrate leads to more efficient charge transport between QWs and suppressed charge recombination in the additive-treated film. As a result, a power conversion efficiency of 14.4% is achieved, which is not only 21% higher than the control one without additive treatment, but also one of the high efficiencies of the low-n (n ≤ 4) AA′ n−1 M n X 3n+1 PSCs. Furthermore, the bare device retains 92% of its initial PCE without any encapsulation after ambient exposure for 1200 h.

Eco-friendly printing is important for mass manufacturing of thin-film photovoltaic (PV) devices to preserve human safety and the environment and to reduce energy consumption and capital expense. However, it is challenging for perovskite PVs due to the lack of eco-friendly solvents for ambient fast printing. In this study, we demonstrate for the first time an eco-friendly printing concept for high-performance perovskite solar cells. Both the perovskite and charge transport layers were fabricated from eco-friendly solvents via scalable fast blade coating under ambient conditions. The perovskite dynamic crystallization during blade coating investigated using in situ grazing incidence wide-angle X-ray scattering (GIWAXS) reveals a long sol-gel window prior to phase transformation and a strong interaction between the precursors and the eco-friendly solvents. The insights enable the achievement of high quality coatings for both the perovskite and charge transport layers by controlling film formation during scalable coating. The excellent optoelectronic properties of these coatings translate to a power conversion efficiency of 18.26% for eco-friendly printed solar cells, which is on par with the conventional devices fabricated via spin coating from toxic solvents under inert atmosphere. The eco-friendly printing paradigm presented in this work paves the way for future green and high-throughput fabrication on an industrial scale for perovskite PVs.