Aqueous Processed All-Polymer Solar Cells with High Open-Circuit Voltage Based on Low-Cost Thiophene-Quinoxaline Polymers.

Eco-friendly solution processing and the low-cost synthesis of photoactive materials are important requirements for the commercialization of organic solar cells (OSCs). Although varieties of aqueous-soluble acceptors have been developed, the availability of aqueous-processable polymer donors remains quite limited. In particular, the generally shallow highest occupied molecular orbital (HOMO) energy levels of existing polymer donors limit further increases in the power conversion efficiency (PCE). Here, we design and synthesize two water/alcohol-processable polymer donors, poly[(thiophene-2,5-diyl)-alt-(2-((13-(2,5,8,11-tetraoxadodecyl)-2,5,8,11-tetraoxatetradecan-14-yl)oxy)-6,7-difluoroquinoxaline-5,8-diyl)] (P(Qx8O-T)) and poly[(selenophene-2,5-diyl)-alt-(2-((13-(2,5,8,11-tetraoxadodecyl)-2,5,8,11-tetraoxatetradecan-14-yl)oxy)-6,7-difluoroquinoxaline-5,8-diyl)] (P(Qx8O-Se)) with oligo(ethylene glycol) (OEG) side chains, having deep HOMO energy levels (∼-5.4 eV). The synthesis of the polymers is achieved in a few synthetic and purification steps at reduced cost. The theoretical calculations uncover that the dielectric environmental variations are responsible for the observed band gap lowering in OEG-based polymers compared to their alkylated counterparts. Notably, the aqueous-processed all-polymer solar cells (aq-APSCs) based on P(Qx8O-T) and poly[(N,N'-bis(3-(2-(2-(2-methoxyethoxy)-ethoxy)ethoxy)-2-((2-(2-(2-methoxyethoxy)ethoxy)ethoxy)-methyl)propyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl)-alt-(2,5-thiophene)] (P(NDIDEG-T)) active layer exhibit a PCE of 2.27% and high open-circuit voltage (VOC) approaching 0.8 V, which are among the highest values for aq-APSCs reported to date. This study provides important clues for the design of low-cost, aqueous-processable polymer donors and the fabrication of aqueous-processable OSCs with high VOC.

On the Conformation of Dimeric Acceptors and Their Polymer Solar Cells with Efficiency over 18 .

The determination of molecular conformations of oligomeric acceptors (OAs) and their impact on molecular packing are crucial for understanding the photovoltaic performance of their resulting polymer solar cells (PSCs) but have not been well studied yet. Herein, we synthesized two dimeric acceptor materials, DIBP3F-Se and DIBP3F-S, which bridged two segments of Y6-derivatives by selenophene and thiophene, respectively. Theoretical simulation and experimental 1D and 2D NMR spectroscopic studies prove that both dimers exhibit O-shaped conformations other than S- or U-shaped counter-ones. Notably, this O-shaped conformation is likely governed by a distinctive "conformational lock" mechanism, arising from the intensified intramolecular π-π interactions among their two terminal groups within the dimers. PSCs based on DIBP3F-Se deliver a maximum efficiency of 18.09 %, outperforming DIBP3F-S-based cells (16.11 %) and ranking among the highest efficiencies for OA-based PSCs. This work demonstrates a facile method to obtain OA conformations and highlights the potential of dimeric acceptors for high-performance PSCs.

Polymer Acceptors with Flexible Spacers Afford Efficient and Mechanically Robust All-Polymer Solar Cells.

High efficiency and mechanical robustness are both crucial for the practical applications of all-polymer solar cells (all-PSCs) in stretchable and wearable electronics. In this regard, a series of new polymer acceptors (PA s) is reported by incorporating a flexible conjugation-break spacer (FCBS) to achieve highly efficient and mechanically robust all-PSCs. Incorporation of FCBS affords the effective modulation of the crystallinity and pre-aggregation of the PA s, and achieves the optimal blend morphology with polymer donor (PD ), increasing both the photovoltaic and mechanical properties of all-PSCs. In particular, an all-PSC based on PYTS-0.3 PA incorporated with 30% FCBS and PBDB-T PD demonstrates a high power conversion efficiency (PCE) of 14.68% and excellent mechanical stretchability with a crack onset strain (COS) of 21.64% and toughness of 3.86 MJ m-3 , which is significantly superior to those of devices with the PA without the FCBS (PYTS-0.0, PCE = 13.01%, and toughness = 2.70 MJ m-3 ). To date, this COS is the highest value reported for PSCs with PCEs of over 8% without any insulating additives. These results reveal that the introduction of FCBS into the conjugated backbone is a highly feasible strategy to simultaneously improve the PCE and stretchability of PSCs.

Printable Off-On Thermoswitchable Fluorescent Materials for Programmable Thermally Controlled Full-Color Displays and Multiple Encryption.

Thermoswitchable fluorescent materials (TFMs) have received special attention due to their unique fluorescent colorimetric responses to temperature. Conventional TFMs generally display unicolor with switching from one color to another, showing unprintable and unsatisfied performances. These limitations greatly hinder their development and expansion toward advanced applications. Herein, the superior integration of full-color, off-on switching mode, printability, and high performance to TFMs is achieved successfully. The success is due to a thermally induced synchronous "dual/multichannel" stimulus-response mode regulated by a self-crystalline phase-change material; that is, synergistic changes of the molecular existence states and subsequent colors/spectra of the fluorescent modifier and fluorophores, accompanied by corresponding high-efficiency on-off switching of Förster resonance energy transfer. These TFMs are simple to prepare and show good performance, such as high fluorescence emission contrast (>100), great reversibility (>200 cycles), and easy-to-adjust response temperature. Particularly, these R/G/B TFMs can be prepared as tricolor fluorescent inks, and thus full-color emissions on flexible substrate can be easily obtained by printing. Finally, their great potential in switchable dynamic interior decoration, programmatic temperature-control information display, and senior information encryption are illustrated. This successful exploration offers a new perspective for designing and optimizing various other switchable materials with higher comprehensive performances.

Photooxidation of oxazolidine molecular switches: uncovering an intramolecular ionization facilitated cyclization process.

Photooxidation of oxazoline (OXA) molecular switches through media-induced intramolecular ionization is reported. The formation of the photooxidation product occurs by attack of the flexible donor group (-CH2CH2OH) to the adjacent C[double bond, length as m-dash]C with 1O2 as the oxidant. The novel seven-membered ring sub-structure of the photooxidation product was inferred by HRMS, IR and 1H NMR spectroscopy. Additionally, acid released from solvent photolysis was found to affect the product formation and efficiency of the photooxidation.

Oxazolidine Transient Bases as Molecular Platforms for Testing Dynamic CO2 Capture in Biochemical Systems.

Understanding the dynamic processes of CO2 capture in biosystems is important because of the great effect CO2 has on the carbon cycle, human health, the global climate, and living environments. After years of multidisciplinary studies, researchers have gained only basic mechanistic knowledge about how enzymes or protein-aggregates capture and deliver CO2, a process involving reversible bonding of CO2 with basic amino acid residues. However, vital mechanistic details of how the activated basic residues within these enzymes or protein-aggregates are initially formed, a crucial step for CO2 capture, are still lacking. Herein, we designed specific molecules, i.e., oxazolidines, which are able to reversibly change their alkalinity via ultrafast isomerizations. Serving as so-called transient bases, these oxazolidines mimic the activated/deactivated states of enzymes or protein-aggregates responsible for dynamic CO2 capture/release. A detailed mechanism for CO2 capture, which involves dynamic covalent bonding and multimolecular cooperative interactions among functional groups that occur with the help of a polyhydroxyl environment, is demonstrated by UV-vis and multiple NMR spectroscopies as well as theoretical calculations. Using suitable oxazolidine transient bases, applications for visual CO2 detection under different detection limit requirements were also developed. Insights for further understanding the process of dynamic CO2 capture in biosystems are also discussed. This oxazolidine-inspired biomimetic CO2 capture serves as a platform for the future development of additional biomimicking systems, as well as offers unique perspectives for other complicated life processes.

Endowing Hydrochromism to Fluorans via Bioinspired Alteration of Molecular Structures and Microenvironments and Expanding Their Potential for Rewritable Paper.

Interest and effort toward new materials for rewritable paper have increased dramatically because of the exciting advantages for sustainable development and better nature life cycle. Inspired by how nature works within living systems, herein, we have used fluorans, as a concept verification, to endow original acidochromic, basochromic or photochromic molecules with broader properties, such as switchable with solvent, water, heat, electricity, stress, other force, etc., via simplified methods (i.e., via variation of submolecular structure or microenvironments). The hydrochromic visual change and reversible behavior of selected molecules have been explored, and the primary mechanism at the atomic or subatomic level has been hypothesized. In addition, several newly demonstrated hydrochromic fluorans have been utilized for water-jet rewritable paper (WJRP), which exhibit great photostability, high hydrochromic contrast, and fast responsive rate and which can be reused at least 30 times without significant variation. The water-jet prints have good resolution and various colors and can keep legibility after a few months or years. This improved performance is a major step toward practical applications of WJRP.

Facile synthesis of manganese oxide loaded hollow silica particles and their application for methylene blue degradation.

A facile poly acrylic acid (PAA) soft templating method was developed to fabricate manganese oxide loaded hollow silica particles (MHSPs). The synthesis involves PAA-Mn aggregation to form spherical particles and silica coating layer formation on the outer surface of the particles. Subsequent calcination in air at 500 °C removes the polymer inside the particles, and hollow silica spheres with trapped metal oxide particles are thus formed. The PAA traps the Mn ions and forms aggregates which template the silica shell formation in this process. The Mn content and the structure of the MHSPs can be tuned by changing doses of the Mn salt initially added. Moreover, decomposition of PAA during calcination endows high surface areas of the MHSPs. Catalytic oxidation of methylene blue (MB) with H2O2 was tested on the MHSPs. The results show that the MHSPs with hollow structure and high surface areas enhance the catalytic activity compare to the corresponding manganese oxide solid particles (MSPs). This strategy can also be used to synthesize other metal oxides (such as MgO and NiO) loaded hollow silica particles.