Research Area
- Perovskite solar cells
Inorganic-organic hybrid lead try-halide based solar cells are the most promising technology in the field of renewable energy research because of its high efficiency and solution processability. In laboratory, the efficiency of perovskite solar cells has reached 20.1%. But the major concern about this new technology is the device stability under ambient condition and under sunlight. We study the mechanism of various degradation processes and solve this problem by chemical and engineering means. The most important factor is the ion migration under light and heat which causes the degradation of perovskite solar cells.
- Polymer nanoparticles in organic electronics: Molecular scale to meso scale self-assembly
Polymer nanoparticles are the building blocks of next generation organic electronics. Efficient charge transport through surfactant stabilized polymer nanoparticles has been demonstrated recently. Internal packing of the polymer nanoparticles is tuned by the choice of solvent, concentration and the surfactant molecules, where as meso-scale packing is controlled by nanoparticle size, shape and surface charge.
- Photocurrent fluctuation in polymer solar cells
Polymer solar cells exhibit unique feature in the noise spectrum originating from the photocurrent. A peak in the range of 20 to 30 kHz in power spectral density is observed along with 1/f noise in the low frequency range. Charge transport properties and degradation process of polymer solar cells can be understood analyzing noise spectroscopy.
- Polymer/Electrolyte interface - a new strategy for single pixel multi-color sensing.
Optical properties of polymer at electrolyte interface has been utilized for multi-color sensing application. The photocurrent signal generated by polymer at the electrolyte interface is very similar to that of mice retina opens up the opportunity for artificial retina device. The wavelength dependent output of these devices can be tuned to detect three primary colors without any filter arrangement.
- Intensity modulated photocurrent response of Bulk-heterojunction polymer solar cells.
A universal feature in the frequency dependence of intensity modulated photocurrent based on studies of a variety of efficient bulk-heterojunction polymer solar cells has been observed. This feature appears in the form of a local maximum in the 5 kHz to 10 kHz range and is observed to be largely independent of the external parameters such as modulated light intensity, wavelength, temperature, and external field over a wide range. A simplistic kinetic model involving carrier generation, recombination and extraction processes is used to interpret the overall essential features of photocurrent spectrum and correlate it to the device parameters.
- Electric field induced instability study on conducting metal alloy and its application in the area of organic electronics.
The behavior of a metallic liquid drop in the presence of an external electric field has been studied. The droplet profile is governed by the stabilizing surface energy and the destabilizing electrostatic energy, with a critical voltage beyond which the droplet becomes unstable. The electric field induced behavior of low melting temperature alloy in the liquid state is utilized in organic electronics devices. It has been observed that the droplet modifications in the linear response regime can be retained upon cooling the drop to the solid state. This procedure can be used as an electrode with precise dimensions for applications in molecular and polymer electronics.
- Area dependence of solar cells efficiency.
Efficiency of an organic solar cell is observed to be dependent on the dimensions of electrode defining the active area. Efficiency of devices follows inverse law with the dimension of the active electrode area. The increase in efficiency for smaller active areas can be explained by the reduced electrical resistive loss, the enhanced optical effects, and the finite additional fraction of photogenerated carriers in the vicinity of the perimeter defined by the metal electrode.
- Polymer electrode interface study of organic/polymer solar cells.
A probable limiting factor for efficiency and fill factors of organic solar cells originates from the cathode-polymer interface. Various forms of cathode layer such as Al, Ca, oxidized Ca, and low melting point alloys have been used in model systems to emphasize this aspect in these studies. Intimate contact (conformal coating of cathode materials) of a polymer/electrode interface gives better fill factor and hence higher efficiency, where as fast deposition of electrode leads to a non-conformal coating and hence reduced fill factor has been observed. Use of low melting point alloy gives a better option to control the interface by changing the phase of the alloy (solid to melt phase).