Highly reproducible organic field-effect transistor from pseudo 3-dimensional triphenylamine-based amorphous conjugated copolymer

An easily accessible 3D donor-acceptor polymer based on triphenylamine (PTPA-co-DTDPP) is synthesized by a simple and efficient route. Owing to its non-fibrillar structure, PTPA-co-DTDPP features highly reproducible charge carrier mobility of up to 3.3 x 10(-3) cm(2) V(-1) s(-1) at various fabrication conditions.close181

Well-defined donor-acceptor rod-coil diblock copolymers based on P3HT containing C-60: the morphology and role as a surfactant in bulk-heterojunction solar cells

The synthesis of well-defined rod-coil block copolymers consisting of P3HT donor and C-60 acceptor chromophores (P3HT-b-P(S(x)A(y))-C-60) in a molecular architecture is reported for use in bulk-heterojunction (BHJ) solar cells. In thin films of the resulting block copolymer, reproducible self-assembly into well-defined "nanofibrils'' is observed. This is the first example of a block copolymer containing a C-60 derivative that shows exclusively a nanofibrilar structure. We have investigated the potential utility of the block copolymer as a "surfactant'' for controlling the interface morphology of the P3HT: PCBM donor-acceptor phase domains within the composite. We find a substantial improvement in device performance when 5% of block copolymer are introduced to the P3HT: PCBM blend system, resulting in ca. 35% improved efficiency relative to the P3HT: PCBM solar cell fabricated without the "surfactant''.close13212

Stepwise heating in Stille polycondensation toward no batch-to-batch variations in polymer solar cell performance

For a given ??-conjugated polymer, the batch-to-batch variations in molecular weight (Mw) and polydispersity index (??) can lead to inconsistent process-dependent material properties and consequent performance variations in the device application. Using a stepwise-heating protocol in the Stille polycondensation in conjunction with optimized processing, we obtained an ultrahigh-quality PTB7 polymer having high Mw and very narrow ??. The resulting ultrahigh-quality polymer-based solar cells demonstrate up to 9.97% power conversion efficiencies (PCEs), which is over 24% enhancement from the control devices fabricated with commercially available PTB7. Moreover, we observe almost negligible batch-to-batch variations in the overall PCE values from ultrahigh-quality polymer-based devices. The proposed stepwise polymerization demonstrates a facile and effective strategy for synthesizing high-quality semiconducting polymers that can significantly improve device yield in polymer-based solar cells, an important factor for the commercialization of organic solar cells, by mitigating device-to-device variations

A synthetic approach to a fullerene-rich dendron and its linear polymer via ring-opening metathesis polymerization

Through the esterification of an acyl chloride functionalized fullerene precursor with dendritic alcohol, a fullerene-rich dendron containing a norbornene unit at the focal point is prepared for ring-opening metathesis polymerization to obtain its linear polymer with a unimodal and narrow molar mass distribution (PDI = 1.08) by a progressive addition of catalysts.close181

High-efficiency polymer solar cells with a cost-effective quinoxaline polymer through nanoscale morphology control induced by practical processing additives

In the quest to improve the performance of polymer solar cells (PSCs) with a view to realizing economic viability, various solvent additives such as 1,8-octanedithiol (ODT), 1,8-diiodooctane (DIO), diphenylether (DPE) and 1-chloronaphthalene (CN) are used in easily obtainable poly(2,3-bis-(3-octyloxyphenyl)-quinoxaline-5,8-dyl-alt-thiophene-2,5-diyl) (TQ1)-based systems with [6,6]-phenyl C71-butyric acid methyl ester (PC71BM) as an acceptor to optimize the active layer nanomorphology. Utilizing a combination of X-ray diffraction (XRD), atomic force microscopy (AFM), and transmission electron microscopy (TEM), we find that the addition of 5% (v/v) CN leads to smoother films, less heterogeneous surface features, and well-distributed TQ1:PC71BM phases, resulting in more balanced charge transport in the devices and a highly efficient power conversion efficiency (PCE) of 7.08%. This is a record for quinoxaline-based PCSs and is also comparable with the hitherto reported highest efficiency of the PSCs in single junction devices. In addition, the PSCs using an inverted device structure show a satisfactory PCE of 5.83% with high stability to ambient exposure, maintaining over 80% of its initial PCE, even after storage in air for more than 1 month.close282

Towards optimization of P3HT:bisPCBM composites for highly efficient polymer solar cells

The optimization of the polymer solar cells based on regioregular poly(3-hexylthiophene) (P3HT) and the bisadduct of phenyl C(61)-butyric acid methyl ester (bisPCBM) is studied thoroughly as a role of solvent-annealing effect as well as different concentration of bisPCBM. In the case of P3HT: bisPCBM of 1 : 0.8 w/w, more balanced electron and hole mobilities are observed, resulting in better performance of the solar cells. Under the best balance conditions such as P3HT: bisPCBM of 1 : 0.8 w/w, the solvent annealing is employed to further clarify the optimization of the devices. Such a treatment leads to the formation of crystalline P3HT domains in the blend films, which is determined by X-ray diffraction, UV-vis spectroscopy, and atomic force microscopy. From our experiment, one can conclude that the best power conversion efficiency of 3.75% is achieved in a layered structure of P3HT: bisPCBM of 1 : 0.8 w/w for a solvent-annealing time of 24 h.close201

Swapping field-effect transistor characteristics in polymeric diketopyrrolopyrrole semiconductors: Debut of an electron dominant transporting polymer

A fact-finding study on thiophenyl diketopyrrolopyrrole (TDPP)-containing polymers for electronically convertible transport characteristics in organic field effect transistors (OFETs) is presented. In the subject of this consideration, a TDPP-based polymer with bis-benzothiadiazole (BisBT) units that serve as powerful electron-deficient building blocks, namely PDTDPP-BisBT, is prepared in order to achieve an n-channel transistor. The resulting polymer shows n-channel dominant ambipolar OFET characteristics and its electron mobility (1.3 x 10(-3) cm(2) V(-1) s(-1)) is found to be one order of magnitude higher than the hole mobility. Besides, the PDTDPP-BisBT OFET performance is independent of film-deposition conditions due to its completely amorphous microstructure, supported by the atomic force microscopy (AFM) and X-ray diffraction (XRD) analyses. Herein, we report an intriguing discovery in sync with our previous studies that TDPP-based polymers can function as a p-type, n-type, or ambipolar organic semiconductor in accordance with the degree of electron affinity of the comonomers.close211

Isomeric iminofullerenes as acceptors in bulk heterojunction organic solar cells

Two stable iminofullerene isomers, [5,6]-open azafulleroid (open APCBM) and [6,6]-closed aziridinofullerene (closed APCBM) enable us to scrutinize the use of these new acceptors in polymer bulk heterojunction (BHJ) solar cells and compare the effects of open trans- and closed trans-annlar subunits. When we compared the performance of both isomer devices, the poly(3-hexylthiophene)(P3HT):open APCBM device demonstrates an enhancement in photocurrent in comparison with the P3HT: closed APCBM device. From the comparative study, we attribute the enhanced current to the lower degree of symmetry of open APCBM. The alteration of fullerene structure from closed to open breaks its high degree of symmetry and consequently leads to an improved bulk heterojunction with the electron donating conjugated polymer.close242

Synthesis of fluorinated analogues of a practical polymer TQ for improved open-circuit voltages in polymer solar cells

In an attempt to further lower the HOMO of a cost-effective polymer poly(2,3-bis-(3-octyloxyphenyl)quinoxaline-5,8-dyl-alt-thiophene-2,5-diyl) (TQ) by adding F atoms onto the existing quinoxaline acceptor within the polymer backbone, we have synthesized two structurally identical fluorinated analogues of TQ (TQ-F (single F) and TQ-FF (double F)), except for the number of F atoms. The effects of inclusion of F atoms on the optical property, nature of charge transport, and molecular organization are thoroughly investigated. The resulting two fluorinated polymers show a decrease in both the HOMO and the LUMO energy levels relative to non-fluorinated TQ. Moreover, the fluorination of the polymer backbone has lowered the HOMOs more than the LUMOs, slightly widening the energy bandgaps as the number of F atoms increases. Thus, use of these polymers in bulk-heterojunction (BHJ) solar cells, in all cases, leads large VOC values. The power conversion efficiency (PCE) of the optimized PSCs based on TQ-F reaches 4.41%. In addition, it is interesting to note that, despite TQ-FF having the PCE that is lower than TQ-F, an unprecedentedly high VOC of 1.00 V is achieved, which is nearly equaled the highest VOC values ever reported for polymers.close4

Efficient and Moisture-Stable Inverted Perovskite Solar Cells via n-Type Small-Molecule-Assisted Surface Treatment

Defect states at the surface and grain boundaries of perovskite films have been known to be major determinants impairing the optoelectrical properties of perovskite films and the stability of perovskite solar cells (PeSCs). Herein, an n-type conjugated small-molecule additive based on fused-unit dithienothiophen[3,2-b]-pyrrolobenzothiadiazole-core (JY16) is developed for efficient and stable PeSCs, where JY16 possesses the same backbone as the widely used Y6 but with long-linear n-hexadecyl side chains rather than branched side chains. Upon introducing JY16 into the perovskite films, the electron-donating functional groups of JY16 passivate defect states in perovskite films and increase the grain size of perovskite films through Lewis acid-base interactions. Compared to Y6, JY16 exhibits superior charge mobility owing to its molecular packing ability and prevents decomposition of perovskite films under moisture conditions owing to their hydrophobic characteristics, improving the charge extraction ability and moisture stability of PeSCs. Consequently, the PeSC with JY16 shows a high power conversion efficiency of 21.35%, which is higher than those of the PeSC with Y6 (20.12%) and without any additive (18.12%), and outstanding moisture stability under 25% relative humidity, without encapsulation. The proposed organic semiconducting additive will prove to be crucial for achieving highly efficient and moisture stable PeSCs