Renqiang Yang

A novel naphthyl side-chained benzodithiophene polymer for efficient photovoltaic cells with a high fill factor of 75%

To study which strategy (extending side chain π-conjugation with single-bonded or fused aromatic rings) is more effective in improving the photovoltaic properties of benzodithiophene (BDT)-based polymers, naphthyl (NP) and biphenyl (BP) units were introduced to the BDT core as conjugated side chains. Two polymers PBDTNP-DTBO and PBDTBP-DTBO based on NP or BP-substituted BDT and 5,6-bis(octyloxy)-4,7-di(thiophen-2-yl)benzo[c][1,2,5]oxadiazole (DTBO) were designed. These two polymers only exhibited small differences in the chemical structure, but great differences in photovoltaic performance. PBDTNP-DTBO showed a high power conversion efficiency (PCE) of 8.79%, with an open-circuit voltage (Voc) of 0.82 V, a short-circuit current density (Jsc) of 14.34 mA cm−2, and a fill factor (FF) of 74.73%, while PBDTBP-DTBO only showed a maximum PCE of 6.69%, with a Voc of 0.75 V, a Jsc of 13.55 mA cm−2, and a FF of 65.86%. Hence, extending the side chain π-conjugation system of a BDT-based polymer with naphthyl is a more effective method to enhance the photovoltaic properties.

Efficient fullerene-free solar cells with wide optical band gap polymers based on fluorinated benzotriazole and asymmetric benzodithiophene

In this work, α- and β-position naphthalene substituents as side chains on asymmetric BDT were used as donor building blocks to build wide bandgap (WBG) donor materials (PαNBDT-T1 and PβNBDT-T1) with fluorinated benzotriazole (T1) as the acceptor unit. The two co-polymers were used to build polymer solar cells (PSCs) with PC71BM or ITIC acceptor material. In ITIC acceptor material based devices, the PαNBDT-T1 co-polymer with a larger dihedral angle between main backbone and naphthalene ring achieved a higher power conversion efficiency (PCE) of 9.60% with improved short-circuit current density (JSC) and fill factor (FF) compared with PβNBDT-T1, which was ascribed to the excellent morphology of the blended film. The open circuit voltage (VOC) was also maintained at a decent level upon introducing these naphthalene rings due to their high ionization potential and low electron density. Interestingly, for PC71BM based devices, the two polymers show a reverse situation compared with an ITIC system. The PβNBDT-T1 with a small dihedral angle between the main backbone and naphthalene rings shows a slightly higher performance than PαNBDT-T1. However, in the PC71BM system, both polymers did not exhibit ideal optical performance due to their unmatched absorption spectrum. These phenomena indicate that the asymmetric BDTs have great potential towards achieving high optical performance with non-fullerene acceptor materials.

Asymmetric 2D benzodithiophene and quinoxaline copolymer for photovoltaic applications

Two novel copolymer donors based on one-dimensional (1D)–two-dimensional (2D) asymmetrical benzodithiophene (BDT) units (BDTPH-H and BDTPH-OR) and 2,3-diphenyl-5,8-di(thiophen-2-yl)quinoxaline (DTQx) were synthesized and compared with one-dimensional or two-dimensional symmetric BDT unit based photovoltaic polymers. Both asymmetrical polymers exhibited promising photovoltaic performance compared with 1D and 2D symmetric BDT polymers. The power conversion efficiency (PCE) of PBDTPH-DTQx based polymer solar cells is 5.6%, with balanced VOC = 0.7 V, JSC = 11.89 mA cm−2 and FF = 67.3%, which is almost the highest PCE compared with similar BDT unit and fluorine-free substituted DTQx based polymer. What is more, PBDTPH-DTQx shows better performance than PBDTPHO-DTQx due to the single phenyl making DTQx more planar and with better π–π stacking than alkoxy phenyl. These findings demonstrate that the 1D–2D asymmetrical BDT units are also applicable to poor planarity fluorine-free substituted quinoxaline acceptor system.

Amplification of near-infrared fluorescence in semiconducting polymer nanoprobe for grasping the behaviors of systemically administered endothelial cells in ischemia treatment

To date, there have been few studies on using fluorescent cell trackers for non-invasively monitoring the inxa0vivo fate of systemically administered cells. This is because only a relatively small number of cells can reach the disease site post systemic infusion, and thus achieving ideal inxa0vivo cell tracking requires that the fluorescent cell trackers should hold combined merits of ultrahigh near-infrared (NIR) fluorescence, negligible interference on cell behavior and function, excellent retention within cells, as well as accurate long-term cell tracking ability. To address this challenge, we herein developed a highly NIR fluorescent nanoprobe (SPN) based on semiconducting π-conjugated polymers (SPs), by synthesis of a NIR SP-emitter, employment of fluorescence resonance energy transfer (FRET) strategy, and optimization of different FRET donor SPs. Due to the 53.7-fold intra-particle amplification of NIR fluorescence, the SPN could track as few as 2000 endothelial cells (ECs) upon intra-arterial injection into critical limb ischemia (CLI)-bearing mice, showing much higher sensitivity in ECs tracking compared with the most popular commercial cell trackers. Whats more, the SPN could provide precise information on the behaviors of systemically injected ECs in CLI treatment including the inxa0vivo fate and regenerative contribution of ECs for at least 21 days.

Regulating Molecular Aggregations of Polymers via Ternary Copolymerization Strategy for Efficient Solar Cells

For many high-performance photovoltaic materials in polymer solar cells (PSCs), the active layers usually need to be spin-coated at high temperature due to the strong intermolecular aggregation of donor polymers, which is unfavorable in device repeatability and large-scale PSC printing. In this work, we adopted a ternary copolymerization strategy to regulate polymer solubility and molecular aggregation. A series of D-A1-D-A2 random polymers based on different acceptors, strong electron-withdrawing unit ester substituted thieno[3,4-b]thiophene (TT-E), and highly planar dithiazole linked TT-E (DTzTT) were constructed to realize the regulation of molecular aggregation and simplification of device fabrication. The results showed that as the relative proportion of TT-E segment in the backbone increased, the absorption evidently red-shifted with a gradually decreased aggregation in solution, eventually leading to the active layers that can be fabricated at low temperature. Furthermore, due to the excellent phase separation and low recombination, the optimized solar cells based on the terpolymer P1 containing 30% of TT-E segment exhibit high power conversion efficiency (PCE) of 9.09% with a significantly enhanced fill factor up to 72.86%. Encouragingly, the photovoltaic performance is insensitive to the fabrication temperature of the active layer, and it still could maintain high PCE of 8.82%, even at room temperature. This work not only develops the highly efficient photovoltaic materials for low temperature processed PSCs through ternary copolymerization strategy but also preliminarily constructs the relationship between aggregation and photovoltaic performance.