Quaternary 2D Transition Metal Dichalcogenides (TMDs) with Tunable Bandgap

Alloying/doping in 2D material is important due to wide range bandgap tunability. Increasing the number of components would increase the degree of freedom which can provide more flexibility in tuning the bandgap and also reduces the growth temperature. Here, synthesis of quaternary alloys Mo_x W_1?x S_2y Se_{2(1?y )} is reported using chemical vapor deposition. The composition of alloys is tuned by changing the growth temperatures. As a result, the bandgap can be tuned which varies from 1.61 to 1.85 eV. The detailed theoretical calculation supports the experimental observation and shows a possibility of wide tunability of bandgap.     

High-Performance All-Polymer Solar Cells Enabled by n-Type Polymers with an Ultranarrow Bandgap Down to 1.28 eV

Compared to organic solar cells based on narrow-bandgap nonfullerene small-molecule acceptors, the performance of all-polymer solar cells (all-PSCs) lags much behind due to the lack of high-performance n-type polymers, which should have low-aligned frontier molecular orbital levels and narrow bandgap with broad and intense absorption extended to the near-infrared region. Herein, two novel polymer acceptors, DCNBT-TPC and DCNBT-TPIC, are synthesized with ultranarrow bandgaps (ultra-NBG) of 1.38 and 1.28 eV, respectively. When applied in transistors, both polymers show efficient charge transport with a highest electron mobility of 1.72 cm² V⁻¹ s⁻¹ obtained for DCNBT-TPC. Blended with a polymer donor, PBDTTT-E-T, the resultant all-PSCs based on DCNBT-TPC and DCNBT-TPIC achieve remarkable power conversion efficiencies (PCEs) of 9.26% and 10.22% with short-circuit currents up to 19.44 and 22.52 mA cm⁻², respectively. This is the first example that a PCE of over 10% can be achieved using ultra-NBG polymer acceptors with a photoresponse reaching 950 nm in all-PSCs. These results demonstrate that ultra-NBG polymer acceptors, in line with nonfullerene small-molecule acceptors, are also available as a highly promising class of electron acceptors for maximizing device performance in all-PSCs.     

In Situ Oxidation Synthesis of p‐Type Composite with Narrow‐Bandgap Small Organic Molecule Coating on Single‐Walled Carbon Nanotube: Flexible Film and Thermoelectric Performance

Although composites of organic polymers or n‐type small molecule/carbon nanotube (CNT) have achieved significant advances in thermoelectric (TE) applications, p‐type TE composites of small organic molecules as thick surface coating layers on the surfaces of inorganic nanoparticles still remain a great challenge. Taking advantage of in situ oxidation reaction of thieno[3,4‐b]pyrazine (TP) into TP di‐N‐oxide (TPNO) on single‐walled CNT (SWCNT) surface, a novel synthesis strategy is proposed to achieve flexible films of TE composites with narrow‐bandgap (1.19 eV) small molecule coating on SWCNT surface. The TE performance can be effectively enhanced and conveniently tuned by poly(sodium‐p‐styrenesulfonate) content, TPNO/SWCNT mass ratio, and posttreatment by various polar solvents. The maximum of the composite power factor at room temperature is 29.4 ± 1.0 µW m^?1 K^?2. The work presents a way to achieve flexible films of p‐type small organic molecule/inorganic composites with clear surface coating morphology for TE application.     

An Ultrahigh Output Rechargeable Electrode of a Hydrophilic Radical Polymer/Nanocarbon Hybrid with an Exceptionally Large Current Density beyond 1 A cm−2

Facile charge transport by a hydrophilic organic radical‐substituted polymer and the 3D current collection by a self‐assembled mesh of single‐walled carbon nanotube bundles lead to the operation of an ultrahigh‐output rechargeable electrode. Exceptionally large current density beyond 1 A cm^?2 and high areal capacity around 3 mAh cm^?2 are achieved, which are 10^1?2 times larger than those of the previously reported so‐called “ultrafast electrodes.” A sub‐millimeter‐thick, flexible, highly safe organic redox polymer‐based rechargeable device with an aqueous sodium chloride electrolyte is fabricated to demonstrate the superior performance.     

High‐Efficiency All‐Small‐Molecule Organic Solar Cells Based on an Organic Molecule Donor with Alkylsilyl‐Thienyl Conjugated Side Chains

Two medium‐bandgap p‐type organic small molecules H21 and H22 with an alkylsily‐thienyl conjugated side chain on benzo[1,2‐b:4,5‐b′]dithiophene central units are synthesized and used as donors in all‐small‐molecule organic solar cells (SM‐OSCs) with a narrow‐bandgap n‐type small molecule 2,2′‐((2Z,2′Z)‐((4,4,9,9‐tetrahexyl‐4,9‐dihydro‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene‐2,7‐diyl)bis(methanylylidene))bis(3‐oxo‐2,3‐dihydro‐1H‐indene‐2,1‐diylidene))dimalononitrile (IDIC) as the acceptor. In comparison to H21 with 3‐ethyl rhodanine as the terminal group, H22 with cyanoacetic acid esters as the terminal group shows blueshifted absorption, higher charge‐carrier mobility and better 3D charge pathway in blend films. The power conversion efficiency (PCE) of the SM‐OSCs based on H22:IDIC reaches 10.29% with a higher open‐circuit voltage of 0.942 V and a higher fill factor of 71.15%. The PCE of 10.29% is among the top efficiencies of nonfullerene SM‐OSCs reported in the literature to date.