Synthesis and Photovoltaic Properties of Copolymers Based on Benzo[1,2-b:4,5-b′]dithiophene and Thiophene with Different Conjugated Side Groups

Recent developments in the synthesis of regioregular thiophene-based conjugated polymers for electronic and optoelectronic applications using nickel and palladium-based catalytic systems

Thiophene-based conjugated polymers are important conjugated polymers due to their exceptional optical and conductive properties, over the past few decades many researchers have designed novel strategies to reach more efficient materials for electronic applications.

High-Performance Polymer Solar Cells Based on a Wide-Bandgap Polymer Containing Pyrrolo[3,4-f]benzotriazole-5,7-dione with a Power Conversion Efficiency of 8.63

A novel donor-acceptor type conjugated polymer based on a building block of 4,8-di(thien-2-yl)-6-octyl-2-octyl-5H-pyrrolo[3,4-f]benzotriazole-5,7(6H)-dione (TZBI) as the acceptor unit and 4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo-[1,2-b:4,5-b']dithiophene as the donor unit, named as PTZBIBDT, is developed and used as an electron-donating material in bulk-heterojunction polymer solar cells. The resulting copolymer exhibits a wide bandgap of 1.81 eV along with relatively deep highest occupied molecular orbital energy level of -5.34 eV. Based on the optimized processing conditions, including thermal annealing, and the use of a water/alcohol cathode interlayer, the single-junction polymer solar cell based on PTZBIBDT:PC71BM ([6,6]-phenyl-C71-butyric acid methyl ester) blend film affords a power conversion efficiency of 8.63% with an open-circuit voltage of 0.87 V, a short circuit current of 13.50 mA cm-2, and a fill factor of 73.95%, which is among the highest values reported for wide-bandgap polymers-based single-junction organic solar cells. The morphology studies on the PTZBIBDT:PC71BM blend film indicate that a fibrillar network can be formed and the extent of phase separation can be mani-pulated by thermal annealing. These results indicate that the TZBI unit is a very promising building block for the synthesis of wide-bandgap polymers for high-performance single-junction and tandem (or multijunction) organic solar cells.

Synthesis of Main Chain Purine-Based Copolymers and Effects of Monomer Design on Thermal and Optical Properties

The ability to incorporate diverse monomeric building blocks enables the development of advanced polymeric materials possessing a wide range of properties that suits them for myriad applications. Herein, that synthetic toolbox is expanded through the first report of purine-based copolymers in which purines are incorporated directly into the polymer main chain. Stille cross-coupling of dibromopurine monomers with benzodithiophene (BDT) comonomers is used to generate these "poly(purine)s", and variations in the substitution pattern of the purine monomer and BDT side-chains provides insight into the role of monomer design on their resultant thermal and photophysical properties. Specifically, thermal analyses show that poly(purine)s exhibit high thermal stability and high glass transition temperatures depending on the BDT side-chain substituents and substitution pattern of the purine-derived comonomer. Furthermore, optical properties measured via UV-vis and fluorescence spectroscopies show dependence on monomer substitution pattern. These findings demonstrate the viability of synthesizing poly(purine)s via metal-catalyzed cross-coupling reactions and highlight the potential to tailor poly(purine) properties via simple alterations of comonomers.

The effect of branching in a semiconducting polymer on the efficiency of organic photovoltaic cells

The impact of branching in a diketopyrrolopyrrole polymer on the performance of polymer–fullerene photovoltaic cells is investigated.

N. A, B. H. Rational design of benzodithiophene based conjugated polymers for better solar cell performance

We present a concise review of conjugated polymers based on benzodithiophenes (BDTs) for high-performance polymer solar cells (PSCs).

Synthesis and properties of low band gap polymers based on thienyl thienoindole as a new electron-rich unit for organic photovoltaics

A series of polymers based on 6-(2-thienyl)-4H-thieno[3,2-b]indole, a new electron-rich unit for organic photovoltaics, was synthesized. The best-performing device demonstrated a power conversion efficiency of 3.35%.

Impact of constitution of the terthiophene-vinylene conjugated side chain on the optical and photovoltaic properties of two-dimensional polythiophenes

The effects of the spatial arrangement of the conjugated side chains of two-dimensional polymers on their optical, electrochemical, molecular-packing, and photovoltaic characteristics were investigated. Accordingly, novel polythiophenes with horizontally (PBTTTV-h) and vertically (PBTTTV-v) grafted terthiophene–vinylene (TTV) conjugated side chains were synthesized that display two and one UV-vis peaks, respectively; the difference is due to the different constitutions of the conjugated side-chains. Because the spatial arrangement affects the molecular self-assembly, PBTTTV-h shows stronger crystallinity than PBTTTV-v, which enhances the charge mobility in devices. Moreover, PBTTTV-h has a lower HOMO energy level (−5.49 eV) than PBTTTV-v (−5.40 eV). Bulk heterojunction solar cells fabricated from PBTTTV-h/PC71BM and PBTTTV-v/PC71BM exhibit power conversion efficiencies of 4.75% and 4.00%, respectively, and Voc values of 800 and 730 mV, respectively, under AM1.5G illumination (100 mW cm(−2)). Thus, the architecture of the TTV conjugated side chains affects the optical, electrochemical, and photovoltaic properties; this study provides more ideas for improving 2-D conjugated polymers for semiconductor devices.