Showing papers by "Mingliang Sun published in 2018"

Rational design of asymmetric benzodithiophene based photovoltaic polymers for efficient solar cells

Abstract: Extending π-conjugation in the benzodithiophene (BDT) side chains has been proven useful to improve the efficiencies of the BDT-based polymer solar cells (PSCs). Herein, combined with a symmetry-breaking strategy of a BDT unit, we further designed a new asymmetric 1D–2D (one dimensional–two dimensional) monomer asy-BDTBP with an alkoxyl group as the 1D part and a π-extending alkoxybiphenyl as the 2D substituted group. Medium band-gap donor–acceptor (D–A) conjugated polymer P1 was synthesized with asy-BDTBP and 4,7-di(4-(2-ethylhexyl)-2-thienyl)-5,6-difluoro-2,1,3-benzothiadiazole (DTffBT) as the donor and acceptor unit, respectively. Encouragingly, P1 blended with PC71BM exhibited an obviously enhanced power conversion efficiency (PCE) compared to the reported symmetric analogue PBDTBP–DTffBT (6.70%). The PCE increased to 8.45% with an open-circuit voltage (VOC) of 0.838 V, a short-circuit current density (JSC) of 14.35 mA cm−2 and a fill factor (FF) of 70.27%. However, P1 coupled with a classical non-fullerene acceptor ITIC revealed a relatively poor efficiency of 6.35% due to the bad complementarity of absorption spectra. To match the absorption of ITIC, a wide band-gap D–A polymer P2 was further designed with a weak electron-withdrawing group benzo[1,2-c:4,5-c′]dithiophene-4,8-dione (BDD) instead of DTffBT as the acceptor unit. As a result, P2 possessed a complementary absorption spectrum with ITIC, and the resulting devices presented an excellent photovoltaic performance. The optimal efficiency boosted to 10.04% with VOC of 0.873 V, JSC of 17.60 mA cm−2 and FF of 65.37%. This work demonstrates the great potential of asymmetric BDTs for high efficient PSCs and the importance of the rational design of polymers for different types of PSCs.

Fusing Benzo[c][1,2,5]oxadiazole Unit with Thiophene for Constructing Wide-bandgap High-performance IDT-based Polymer Solar Cell Donor Material.

Abstract: Benzo[c][1,2,5]oxadiazole (BO) moiety is a strong electron-withdrawing unit compared to benzo[c][1,2,5]thiadiazole (BT). It is usually introduced as an acceptor to construct narrow band-gap donor-acceptor (D-A) materials. Herein, the -extended conjugated moiety dithieno[3',2':3,4 '';2,3 '':5,6]-benzo[1,2-c][1,2,5]oxadiazole (BOT) was adopted as the acceptor moiety to design D-A polymers. Considering the more extended pi-conjugated molecular system of BOT compared to the BO unit, a narrower optical band-gap is expected for BOT-based IDT polymer (PIDT-BOT). Unexpectedly, the UV-vis absorption spectra of PIDT-BOT films display a great hypochromatic shift of about 60 nm compared to a BO-based analog (PIDT-BO). The optical band-gaps of the materials are broadened from 1.63 eV (PIDT-BO) to 2.00 eV (PIDT-BOT) accordingly. Although the range of external quantum efficiency (EQE) of PIDT-BOT-based polymer solar cell (PSC) devices is not as wide as for PIDT-BO-based devices, the EQE response intensities of the PIDT-BOT based device are evidently high. As a result, PSC devices based on PIDT-BOT reveal the best power conversion efficiency at 6.08%.

Single-Component Oligomer Nanoparticle-Based Size-Dependent Dual-Emission Modulation

Abstract: Multichromophoric oligomers offer a versatile platform for nanoparticle multicolor fluorescent modulation. A donor–acceptor–donor (D–A–D) type oligomer (DDBTD), with blue emitting antenna and red emitting core, is chosen to assemble into fluorescent colloidal nanoparticles (FCNs) using a nanoprecipitation method. By modulating the DDBTD concentrations in good solvent, the DDBTD nanoparticles with average diameters ranging from sub-10 to 300 nm are obtained by the nanoprecipitation process in aqueous solution. Interestingly, multicolor photoluminescence (PL) can be realized from bright blue (∼440 nm) to rose red (∼630 nm) based on FCNs size control. The size-dependent PL originates from the aggregation-enhanced fluorescence resonance energy transfer (FRET) from diphenyl-aminofluorenyl antenna unit (blue emitter) to benzothiadiazole-based core (red emitter). Furthermore, the lifetime measurement of the FCNs in excited state shows a size-dependent behavior, which confirms that the size-dependent multicolor P...