Yuvraj Patil

Aggregation induced emission and mechanochromism in tetraphenylethene substituted pyrazabole

Tetraphenylethene (TPE) substituted pyrazabole 2 was designed and synthesized by the Pd-catalyzed Suzuki cross-coupling reaction. The pyrazabole exhibits strong aggregation induced emission (AIE) and reversible mechanochromic behavior with high color contrast between blue and green. The powder XRD studies show that destruction of crystalline state into amorphous state is responsible for mechanochromism.

Small molecule carbazole-based diketopyrrolopyrroles with tetracyanobutadiene acceptor unit as a non-fullerene acceptor for bulk heterojunction organic solar cells

Herein, we investigated the photovoltaic properties of carbazole-based diketopyrrolopyrroles with tetracyanobutadiene acceptor units as highly efficient non-fullerene acceptors together with a D–A conjugated polymer, P, as a donor for polymer solar cells. After optimization, i.e. donor to acceptor weight ratio and solvent vapour annealing, the polymer solar cells exhibited power conversion efficiencies of up to 4.86% and 7.19% for DPP7 and DPP8 as acceptors, respectively. These results indicate that slight changes in the chemical structure of the small acceptor molecule significantly increase the efficiency of the device. The design and synthesis of these non-fullerene acceptors with broader absorption spectra extended towards the near infrared region may be key for the further development of high-performance and cost-effective solution-processed organic solar cells.

Ferrocene-diketopyrrolopyrrole based non-fullerene acceptors for bulk heterojunction polymer solar cells

Herein we have investigated the photovoltaic properties of ferrocenyl tetracyanobutadiene derivatives of diketopyrrolopyrroles SM1 and SM2 as efficient non-fullerene acceptors along with a donor–acceptor (D–A) conjugated polymer P as a donor for polymer solar cells. The solar cell devices showed a maximum power conversion efficiency of 6.44% and 6.89% for the vacuum dried P:SM1 and P:SM2 active layers respectively. The solar cells based on SM2 showed higher PCE compared to SM1 which may be due to the larger values of both Jsc and FF. The results presented here demonstrate that employing ferrocene as a donor unit can provide great scope for the molecular design of highly efficient non-fullerene acceptors and provides important progress in the development of non-fullerene organic solar cells.

Symmetrical and unsymmetrical triphenylamine based diketopyrrolopyrroles and their use as donors for solution processed bulk heterojunction organic solar cells

Two small molecules DPP3 (D–π–A) and DPP4 (D–π–A–π–D) with triphenylamine (TPA) donors and diketopyrrolopyrrole (DPP) acceptors linked with ethyne linkers were designed and synthesized by the Pd-catalyzed Sonogashira cross-coupling reaction. Their photonic, electronic, thermal and computational properties were investigated. The red shift in the electronic absorption spectra of DPP4 as compared to DPP3 is related to extended conjugation and increased donor–acceptor interaction. We have used DPP3 and DPP4 as electron donors along with PC71BM as an electron acceptor for solution processed bulk heterojunction organic solar cells. The solar cells prepared from DPP3:PC71BM and DPP4:PC71BM (1 : 2) processed from chloroform (CF) exhibit a power conversion efficiency (PCE) of 2.23% (Jsc = 6.74 mA cm−2, Voc = 0.92 V and FF = 0.36) and 3.05% (Jsc = 8.26 mA cm−2, Voc = 0.88 V and FF = 0.42), respectively. The higher PCE of the device with DPP4 compared to DPP3 was demonstrated as to the higher hole mobility and broader IPCE spectra. The devices based on DPP3:PC71BM and DPP4:PC71BM processed with solvent additive (1 v% DIO, 1,8-diiodooctane) showed PCE values of 4.06% and 5.31%, respectively. The device optimization results from the improvement of the balanced charge transport and better nanoscale morphology induced by the solvent additive.

Near-infrared absorbing tetracyanobutadiene-bridged diketopyrrolopyrroles

In order to investigate the effects of end capping donors and secondary acceptors on the photonic and electrochemical properties of diketopyrrolopyrrole (DPP), the tetracyanobutadiene (TCBD) bridged D–A1–A2–π–D type DPPs V–VII have been designed and synthesized by a [2+2] cycloaddition–retroelectrocyclization reaction. Optical, thermal, electrochemical and computational studies are performed and compared with their para N-phenyl carbazole-based analogue DPP-VIII. The TCBD bridged DPPs V–VIII exhibit electronic absorption in the visible to near infrared (NIR) region with low HOMO–LUMO gap values compared to their acetylene bridged precursors DPPs I–IV. The DPPs V–VIII exhibit excellent thermal stability. Electrochemical studies reveal additional reduction waves in DPPs V–VIII corresponding to two successive reductions of the TCBD moiety. The introduction of electron-withdrawing TCBD to acetylene-bridged DPPs extends the absorption and lowers the HOMO–LUMO gap which is supported by computational calculations.

Diketopyrrolopyrrole-Based and Tetracyano-Bridged Small Molecules for Bulk Heterojunction Organic Solar Cells

Research on bulk heterojunction organic solar cells has rapidly grown over the past two decades, and device performance has reached power conversion efficiencies over 13 %. In this focus review, we highlight design strategies used for the development of diketopyrrolopyrrole- and tetracyano-based molecular donors. We also describe how tetracyano-bridged non-fullerene acceptors can be developed by a click-type [2+2]-cycloaddition-electrocyclic ring-opening reaction of acetylene-bridged small molecules with tetracyanoethylene by simple modification.

Small Molecule Based Non-Fullerene Acceptors: A Comparative Study

Organic solar cells (OSCs) have gained attention of the scientific community from the last decade and are now considered as one of the most important source for low-cost power production. The recent rapid progress in non-fullerene acceptors in BHJ indicates that they have potential to compete with fullerene-based BHJ OSCs. The present review addressed the systematic comparison among various acceptors (diketopyrrolopyrrole (DPP), benzothiadiazole (BTD) and perylenediimide (PDI) based acceptors) in order to design and improve the performance of small molecules based non-fullerene acceptors. This review focuses on the performance of small molecule non-fullerene acceptors based on DPP, BTD and PDI for OSCs with respect to the change in molecular structures, energy levels, and PCE. A systematic comparison on the effect of molecular architecture, side chains on their performance is provided with the intention of evaluating the challenge to make highly efficient acceptors for the next generation organic photovoltaics.