Research

Organic Materials for Molecular Electronics

Research activities of our group are focused on exploring the manifold of molecular electronics ranging from organic photovoltaics, light-emitting diodes and field-effect transistors. Our interdisciplinary approach includes synthesizing multifunctional conjugated polymers and oligomers with novel properties and studying their characteristics working at the interface of chemistry, physics and materials engineering. We take advantage of molecular structures to fine tune the desired properties through molecular design and robust synthetic strategies.

The group at present is actively engaged in developing organic materials for-

  • Organic Solar Cells
  • Organic Field-Effect Transistors
  • Thermally Activated Delayed Fluorescence (TADF)
  • Singlet Fission
  • Electrochemical Energy Storage Device

Singlet Fission and Thermally Activated Delayed Fluorescence

Spin density encodes intramolecular singlet exciton fission in pentacene dimers

In organic chromophores the first excited singlet and the lowest triplet energy gap is very important in determining its physical and optical properties. Whereas a low energy gap makes it suitable for delayed fluorescence, a high enough energy gap where the triplet is near about half the first excited singlet energy makes it favorable for a phenomenon called Singlet Fission. In our group we explore molecular design principles that allow us to modulate this energy gap for various applications in Organic photovoltaics (OLED’s and Solar Cells). We investigate the excited state dynamics with various steady state and time resolved spectroscopic techniques to understand the various recombination processes, exciton dynamics and charge carrier generation for optimised in-house fabrication of organic photovoltaic devices.

Singlet Fission (SF) is a bichromophoric process whereby a singlet exciton is converted to two triplet excitons through an overall spin conserved process. The initially excited chromophore in its singlet state (S1) decays to its lowest triplet simultaneously exciting another coupled chromophore in its ground state to its lowest triplet state. The singlet state must be nearly double the energy of the triplet state for the molecule to undergo efficient SF which inherently limits the abundance of molecules that exhibit SF. Despite the many challenges, its potential in photovoltaics attracted wide attention in understanding this complex photophysical process in an effort to make it a viable alternative. Our group specialises in designing new materials to explore the mechanistic aspects of singlet fission as well as for application is practical devices. With the help of femtosecond transient absorption spectroscopy and other transient spectroscopic techniques we investigate the detailed excited dynamics in a wide range of molecules from small molecules to molecular dimers and oligomers. Presently, we are involved in understanding the role of CT states and spin densities in singlet fission kinetics. Apart from this we are also concentrated on understanding and realising a long ridden problem in singlet fission, harvesting free triplets for practical applications through both molecular design and device fabrications. Recently, we showed that spin density localisation is crucial in dictating singlet fission kinetics in diketopyrrolopyrrole bridged pentacene dimers. We are also investigating the possibility of exploring biradicaloid nature in chromophores as viable alternatives for SF materials.

Thermally Activated Delayed Fluorescence is a phenomenon commonly observed in organic chromophores with low singlet-triplet energy gap making thermally assisted reverse intersystem crossing feasible. This results in a delayed fluorescence with a much higher lifetime than normally observed in spontaneous emission. Thermally Activated Delayed Fluorescence (TADF) has known applications in Organic Light Emitting Diodes (OLEDs).

Representative Publications:

  • KC Krishnapriya, Palas Roy, Boregowda Puttaraju, Ulrike Salzner, Andrew J Musser, Manish Jain, Jyotishman Dasgupta and Satish Patil, Spin Density Encodes Intramolecular Singlet Exciton Fission in Pentacene Dimers, Nat. Comm. 2019, 10.1038/s41467-018-07736-3.
  • KC Krishnapriya, AJ Musser, S Patil, Molecular design strategies for efficient intramolecular singlet exciton fission, ACS Energy Letters 4 (1), 192-202.
  • T Mukhopadhyay, AJ Musser, B Puttaraju, J Dhar, RH Friend, S Patil, Is the chemical strategy for imbuing “polyene” character in diketopyrrolopyrrole-based chromophores sufficient for singlet fission?, The Journal of Physical Chemistry Letters 8 (5), 984-991

Organic Photovoltaics

Representative Publications:

  • Yaping Zang, Suman Ray, E-Dean Fung, Anders Borges, Marc H Garner, Michael L Steigerwald, Gemma C Solomon, Satish Patil and Latha Venkataraman, Resonant Transport in Single Diketopyrrolopyrrole Junctions, J. Am.Chem. Soc. 2018, 140 (41), 13167–13170.
  •  AA Mohapatra, Y Dong, P Boregowda, A Mohanty, A Sadhanala, X Jiao, Rational Design of Donor–Acceptor Based Semiconducting Copolymers with High Dielectric Constants, The Journal of Physical Chemistry C 125 (12), 6886-6896
  • AA Mohapatra, V Tiwari, S Patil, Energy transfer in ternary blend organic solar cells: recent insights and future directions, Energy & Environmental Science 14 (1), 302-319
  • C. Kanimozhi, N. Y. Gross, K. W. Chou, A. Amassian, T. D. Anthopoulos and and S.Patil, Diketopyrrolopyrrole-Diketopyrrolopyrrole-based Conjugated Copolymer for High-Mobility Organic Field-Effect Transistors, J. Am. Chem. Soc. 2012, 134, 16532.
  • Nidhi Sharma, Shiv Kumar, Yogesh Chandrasekaran, Satish Patil*, Maleimide–based donor-π-acceptor-π-donor derivative for efficient organic light-emitting diodes, Organic Electronics, 2016, 38 180-185
  • Tushita Mukhopadhyay, Boregowda Puttaraju, Satyaprasad P. Senanayak, Aditya Sadhanala, Richard Friend, Hendrik A. Faber, Thomas D. Anthopoulos, Ulrike Salzner, Andreas Meyer, and Satish Patil*, Air-Stable n-channel Diketopyrrolopyrrole−Diketopyrrolopyrrole Oligomers for High Performance Ambipolar Organic Transistors, ACS Appl. Mater. Interfaces, 2016, 38, 25415–25427
  • Satyaprasad P. Senanayak, A. Z. Ashar, Catherine Kanimozhi, Satish Patil, and K. S. Narayan, Room-temperature bandlike transport and Hall effect in a high-mobility ambipolar polymer, Phys. Rev. B, 2015, 91, 115302
  • Sebastian Albert-Seifried, Doo-Hyun Ko, Sven Hüttner, Catherine Kanimozhi, Satish Patil, Richard H Friend, Efficiency limitations in a low band-gap diketopyrrolopyrrole-based polymer solar cell, Phys. Chem. Chem. Phys., 2014, 16, 6743-6752
  • Raja Bhaskar Kanth Siram, Meera Stephen, Farman Ali, and Satish Patil*, Investigation of Phase Separation in Bulk Heterojunction Solar Cells via Supramolecular Chemistry, J. Phys. Chem. C, 2013, 117, 9129–9136

Electrochemical Energy Storage Devices

Demonstration of 12 V / 50 W-250 Wh 8-cell stack of Soluble Lead Redox Flow Battery

Redox Flow Batteries

Redox flow batteries (RFBs) offer an opportunity to make renewable energy storage more affordable and could accelerate prospects for utility-scale development of solar/wind energy storage. RFBs can be almost instantly recharged by replacing the liquid electrolyte. RFBs can be cycled more often and can lend themselves to 100% depth-of-discharge with no negative effects on performance unlike lead-acid and lithium-ion batteries with depths-of-discharge of 60 and 80%, respectively. RFBs can also last for decades (up to 25 years) before being replaced, making them promising for large utility applications, micro-grids and off-grid projects. Our group is currently working on both aqueous and non-aqueous redox flow batteries.

 

Soluble Lead Redox Flow Battery

Soluble lead redox flow batteries (SLRFBs) present several advantages over competing flow battery systems. SLRFBs make use of variable oxidation states of lead. In its simplest form, Pb2+-ions are dissolved in a less toxic and cost-effective aqueous methanesulfonic acid medium as electrolyte that flows through the cells without expensive separators. There are, of course, challenges to surmount such as those related to phase changes at both the positive and negative electrodes. The major challenges are formation of Pb dendrites, PbO2 sludge, O2 evolution and shunt current effect in stacks. Our work is based on addressing each of these problems systematically by studying the effect of binary additives in the electrolyte and achieving extended cycle life of SLRFB. To bring the concepts into context, we have designed, developed and demonstrated the first-ever fully functional SLRFB stack (12 V / 250 Wh) comprising 8-cells with 500 cm2 electrode active area. Developing a stack has its own challenges, for example, occurrence of shunt current. We have studied the origin of shunt current and proposed a novel method to measure and minimize its effect on SLRFB stack. We are currently working towards scaling up the SLRFB technology to demonstrate 1 kWh stack. The studies in our group are primarily directed to propel SLRFBs from laboratory scale to a functional system by addressing key issues of scaling-up materials, fabrication and engineering.

Schematic of an all-organic redox flow battery with Unisol blue and TDPP-Hex-CN4 as positive and negative electrolyte, respectively.

All Organic Non-Aqueous Redox Flow Battery

Organic redox flow batteries (ORFBs) are attractive candidates for large-scale energy storage devices owing to its advantages in terms of cost, structural tunability, molecular diversity, and natural abundance. The operating cell voltages in aqueous redox flow batteries are limited to 1.23 V as beyond this voltage water electrolysis will be taking place leading to oxygen and hydrogen evolution. By contrast non-aqueous redox flow batteries can theoretically deliver the cell voltage up to 4V while utilizing stable organic solvents (e.g. acetonitrile, propylene carbonate and dimethoxyethane etc.) and suitable organic redox active couples. Apart from limited solubility, lack of high-performance membranes and low electrolyte conductivity, stability of constituent electrolyte materials is one of the major issues impeding the development of non-aqueous redox flow batteries. Both redox-active molecules need to be stable during charge-discharge cycling operations while being repeatedly oxidized and reduced with negligible degradation in performance. In this regard, stable anolytes are rare, primarily because of the low stability in the presence of oxygen and moisture. Our group is investigating the suitability of Diketopyrrolopyrrole derivatives as stable anolytes for all organic non aqueous redox flow battery.

Recent Publications

  • Rathod, S.; Jaiswal, N.; Ravikumar, M. K.; Patil, S.; Shukla, A. Effect of Binary Additives on Performance of the Undivided Soluble-Lead-Redox-Flow Battery. Electrochimica Acta 2021, 365, 137361.
  • Sharma, S.; Rathod, S.; Yadav, S.P.; Chakraborty, A.; Shukla, A.; Aetukuri, N.; Patil, S. Electrochemical Evaluation of Diketopyrrolopyrrole Derivatives for Non-aqueous Redox Flow Battery. Chemistry – A European Journal, 2021, manuscript ID chem. 202003279, (Accepted)
  • Rathod, S.; Ravikumar, M. K.; Jaiswal, N.; Patil, S.; Shukla, A. Extending cycle-life of the soluble-lead-redox-flow-battery with an auxiliary gas-diffusion electrode: A Proof-of-Concept study. Ionics, 2021, manuscript ID IONICS-2020-0813, (Accepted)
  • Ravikumar, M. K.; Rathod, S.; Jaiswal, N.; Patil, S.; Shukla, A. The Renaissance in Redox Flow Batteries. Journal of Solid State Electrochemistry 2016, 21, 2467-2488.

 

Patents

  • Shukla, A.K.; Patil, S.; Ravikumar, M.K.; Rathod. S.; Jaiswal, N.; Chandok, J.S.; Singh, V.; Ojha, S. (2019) Soluble Lead Redox Flow Battery with Auxiliary Electrode. Indian patent Application no. 201841025622.
  • Patil, S.; Shukla, A.K.; Aetukuri, N.; Rathod. S.; Sharma, S. (2019) Diketopyrrolopyrrole Based Derivative as Stable Anolyte for Organic Redox Flow Batteries. Indian patent Application no. 201941039240.
  • Shukla, A.K.; Patil, S.; Ravikumar, M.K.; Rathod. S. (2021) Cost-effective soluble lead redox flow battery with prophylactic electrolyte additives. Indian patent Application no. 202141001976

 

Conference papers

  • Suman, R. ; Ravikumar, M. K.; Jaiswal, N.; Patil, S.; Shukla, A. K. On Extending Cycle-Life of the Soluble Lead Redox Flow Battery. ECS Meeting Abstracts 2018,MA2018-01(2): 221.
  • Suman, R.; Ravikumar, M. K.; Jaiswal, N.; Patil, S.; Shukla, A. K. Effect of Sodium Fluoride and Sodium Lignosulphonate Additives on Performance of the Soluble Lead Redox Flow Battery. ECS Meeting Abstracts 2019, MA2019-01(3): 419.
  • Sharma, S.; Suman, R.; Ray, S.; Aetukuri, N.; Shukla, A. K.; Patil, S. Diketopyrrolopyrrole Based Derivative for Non-Aqueous Redox Flow Battery. ECS Meeting Abstracts 2019, MA2019-01(3): 449.
  • Sharma, S.; Suman, R.; Yadav, S.P.; Chakraborty, A.; Shukla, A.; Aetukuri, N.; Patil, S. Diketopyrrolopyrrole Based Organic Anolyte for Non-Aqueous Organic Redox Flow Battery. ACS Spring 2021, Paper ID: 3555863