Abhay Gusain

Investigation on the effects of thermal annealing on PCDTBT:PCBM bulk-heterojunction polymer solar cells

Bulk heterojunction solar cells of 3×3 array have been fabricated using a blend of PCDTBT:PCBM as active layer. Among nine devices fabricated, the best device exhibited efficiency 5% with standard deviation ∼ 20% in efficiency. Thermal annealing of the devices resulted in decrease of photovoltaic properties of all devices which was attributable to the change at the active layer/cathode interface of devices as supported by electrical and spectroscopic studies.

Graphene composite for improvement in the conversion efficiency of flexible poly 3-hexyl-thiophene:[6,6]-phenyl C71 butyric acid methyl ester polymer solar cells

The solution of thin graphene-sheets obtained from a simple ultrasonic exfoliation process was found to chemically interact with [6,6]-phenyl C71 butyric acid methyl ester (PCBM) molecules. The thinner graphene-sheets have significantly altered the positions of highest occupied molecular orbital and lowest unoccupied molecular orbital of PCBM, which is beneficial for the enhancement of the open circuit voltage of the solar cells. Flexible bulk heterojunction solar cells fabricated using poly 3-hexylthiophene (P3HT):PCBM-graphene exhibited a power conversion efficiency of 2.51%, which is a ∼2-fold increase as compared to those fabricated using P3HT:PCBM. Inclusion of graphene-sheets not only improved the open-circuit voltage but also enhanced the short-circuit current density owing to an improved electron transport.

Effect of Co-sensitization and acid treatment on TiO2 photoanodes in dye-sensitized solar cells

The performance of dye-sensitized solar cells is improved by simple formic acid treatment of TiO2 photoanodes. The treatment increases number of hydroxyl groups at TiO2 surface and thereby result in enhanced dye-loading and device efficiency. The best device showed an open circuit voltage of 0.62V, short-circuit current density 6.34mA/cm2, fill factor of 60%, and a power conversion efficiency of ∼12 % under 20mW/cm2 white light illumination.

Poly(2,7-carbazole) derivative based air stable and flexible organic field effect transistor

Poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) which is known to be air stable, has been used as active layer to fabricate flexible organic field effect transistor. Poly(methyl methacrylate) has been used as gate dielectric. The mobility and on-off ratio for these devices were found to be 7×10−4cm2V−1s−1 and 1.5×102, respectively.

Interfacial charge trapping in the polymer solar cells and its elimination by solvent annealing

The PCDTBT:PCBM solar cells were fabricated adopting a tandem layer approach to investigate the critical issues of charge trapping, radiation absorption, and efficiency in polymer solar cells. This layered structure was found to be a source of charge trapping which was identified and confirmed by impedance spectroscopy. The low efficiency in multilayered structures was related to trapping of photo-generated carriers and low carrier mobility, and thus an increased recombination. Solvent annealing of the structures in tetrahydrofuran vapors was found beneficial in homogenizing the active layer, dissolving additional interfaces, and elimination of charge traps which improved the carrier mobilities and eventually the device efficiencies.

Efficiency enhancement in PCDTBT:PCBM solar cells using graphene nanosheets

Experiments were carried out to improve the efficiency of PCDTBT:PCBM solar cells using thinner graphene sheets as an additive in the hole transport layer (HTL) and active layers of these solar cells. The required graphene nano-sheets were exfoliated by mechanical process using rigorous sonication of graphene flakes. It has been found that devices with graphene nanosheets mixed in the HTL have shown improvement in the efficiency, however other devices shown a degradation. The improvement in the efficiency in the devices has been attributed to the improved charge transport for photo-generated carriers across the interfaces.

Conducting polymers based counter electrodes for dye-sensitized solar cells

Conducting polymer films were synthesized and employed as an alternative to expensive platinum counter electrodes for dye-sensitized solar cells. poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) thin films were spin-coated and polypyrrole films were electrochemically deposited via cyclic voltammetry method on ITO substrates. The morphology of the films were imaged by SEM and AFM. These films show good catalytic activity towards triiodide reduction as compared to Pt/FTO electrodes. Finally the photovoltaic performance of DSSC fabricated using N3 dye were compared with PT/FTO, PEDOT/ITO, and e-PPy counter electrodes.

Improved efficiency of organic dye sensitized solar cells through acid treatment

We have improved the efficiency of the dye sensitization solar cells (DSSCs) by adopting an innovative and simpler methodology of oxalic acid treatment of TiO2. It is observed that the efficiency of the DSSC is improved to 2.3% after treatment. The improvement has been understood in terms of reduced dark current and enhanced dye loading as supported by UV-Visible, electrical and electrochemical impedance measurements.