Vishal Bharti

Diacetylene bridged triphenylamines as hole transport materials for solid state dye sensitized solar cells

We have synthesized and characterized a series of triphenylamine-based hole-transport materials (HTMs), and studied their function in solid-state dye sensitized solar cells (ss-DSSCs). By increasing the electron-donating strength of functional groups (–H < –Me < –SMe < –OMe) we have systematically shifted the oxidation potential and ensuing photocurrent generation and open-circuit voltage of the solar cells. Correlating the electronic properties of the HTM to the device operation highlights a significant energy offset required between the Dye – HTM highest occupied molecular orbital (HOMO) energy levels. From this study, it is apparent that precise control and tuning of the oxidation potential is a necessity, and usually not achieved with most HTMs developed to date for ss-DSSCs. To significantly increase the efficiency of solid-state DSSCs understanding these properties, and implementing dye-HTM combinations to minimize the required HOMO offset is of central importance.

Improved hole mobility and suppressed trap density in polymer-polymer dual donor based highly efficient organic solar cells

Here we report, the charge transport properties of polymer-polymer dual donor blended film, viz., polythieno[3,4-b]-thiophene-co-benzodithiophene (PTB7) and poly [N-9″-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′benzothiadiazole) (PCDTBT) in the optimized concentration. Trap density and hole mobility in polymer-polymer (PTB7-PCDTBT) dual donor system have been studied by means of current density–voltage (J-V) characteristics at various temperatures, i.e., 280 K–120 K in hole only device configuration, i.e., indium tin oxide/poly(3,4-ethylenedioxythiophene):poly(styrenesulphonate) (PEDOT:PSS)/Polymer film/gold (Au). The J-V curves exhibit the space charge limited conduction behavior. The corresponding hole mobility for PTB7 and PCDTBT are 3.9 × 10−4 cm2 V−1 s−1 and 2.1 × 10−4 cm2 V−1 s−1, respectively, whereas it is 9.1 × 10−4 cm2 V−1 s−1 in the polymer-polymer blend of PTB7:PCDTBT (0.7:0.3). This enhancement in mobility can be attributed to the suppressed trap density in PTB7:PCDTBT (0...

In-situ Growth of CdS Nanorods in PTB7 by Solvothermal Process for Hybrid Organic Inorganic Solar Cell applications

We demonstrate a high yielding, green approach using solvothermal, in situ growth of CdS nanorods (NRs) in a low band gap polymer, poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b’]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl] thieno[3,4-b]thiophenediyl]] (PTB7). The use of chloroaniline dithiocarbamate and chloroaniline as ligands to functionalize the Cd (II) ions provides a new path for solubilization of Cd (II) complex in the chlorobenzene solvent. It removes use of volatile and hazardous chemicals such as pyridine as ligand which are conventionally used to enhance solubility of such complexes. It is the first example of solvothermal process used for in situ growth of CdS NRs in a polymer matrix. This nanocomposite is used to fabricate hybrid-organic–inorganic-solar cells (HOISC) as donor–acceptor combination in the bulk hetrojunction (BHJ) geometry. The incorporation of CdS NRs shows significant decrease in the band gap of PTB7 from 1.71 eV to 1.59 eV and the photoluminescence (PL) studies show significant quenching in the PL of PTB7 by the addition of CdS NRs. This suggests that the PTB7:CdS NRs is a potential nanocomposite for the bulk heterojunction active layer in the HOISCs. The HOISCs fabricated using the PTB7:CdS as donor–acceptor combination give power conversion efficiency of the order of 1.16 %. This work has implication in the development of green economical and efficient HOISC by using highly controlled synthetic process.

Sustainable Organic Polymer Solar Cells Using TiO2 Derived From Automobile Paint Sludge

We demonstrate green synthesis of TiO2 nanoparticles (Nps) derived from automobile paint sludge (APG) and its application in the development of sustainable and solution processable polymer solar cells (PSCs). The APG contains TiO2 > 35 % of its weight with several surfactants, organic polymers and ~ 2 to 10 % inorganic matter depending on the type of paints used. The TiO2 is generally present as micro sized particles in the APG which on hydrothermal treatment transform into nano sized particles. These organic matter is thermally extracted by a specially designed reaction vessel, where as the inorganic impurities are removed by repeated washing with dilute acids and bases. The TiO2 Nps are characterized by SEM imaging, EDX analysis, powder XRD, TG/DTA and FTIR, spectroscopy techniques. The TiO2 Nps are re-suspended in methanol for application in PSCs as an efficient electron transport layer. The TiO2 layer was spin coated on bulk hetero junction active layer of low band gap donor polymers P3HT with PCBM as electron acceptor. The performance of the TiO2 Nps is analyzed by fabricating devices in ITO/PEDOT:PSS/active layer/TiO2/Al configuration. The present work has implication for ultra low cost and sustainable PSCs with advantage of recycling of a highly hazardous industrial waste.

Charge Transport Studies in Pure and CdS Doped PBDTTPD:CdS Nanocomposite for Solar Cell Application

The recent trends in organic photovoltaic is towards the development of hybrid solar cells using the active absorption layer of a nancomposite layer having conjugated polymer incorporated with inorganic quantum dots, nanorods, nanoparticles, etc. The dispersion of nanomaterials in polymer matrix leads to inadequate charge transfer, agglomeration etc., which is a hindrance towards achieving high efficiency in the hybrid solar cells. On the other hand if nanomaterials are grown in situ into polymer matrix, it may enable to overcome the above disadvantage. Keeping this in view, we have synthesized a nanocomposite of PBDTTPD:CdS by in situ growth of CdS nanorods into polymer matrix. The charge transport mechanism was studied and the nanocomposite showed improvement in charge carrier mobility over the pure polymer which has been attributed to improvement in inter-chain charge transport by the presence of inorganic nanocrystals in polymer matrix.

Realization of highly efficient polymer solar cell based on PBDTTT-EFT and [71]PCBM

In this work, we have fabricated highly efficient polymer solar cells based on the blend of PBDTTT-EFT:PC71BM in the inverted device configuration. By using low temperature processed zinc oxide (ZnO) nanoparticles as an electron-transport layer (ETL) and 1,8-diiodooctane (DIO) as additive in chlorobenzene (CB) solvent we have achieved PCE of 9.43% with an excellent short-circuit current density (Jsc) of 17.6 mAcm−2, open circuit voltage (Voc) of 0.80 V and fill factor (FF) of 0.67. These results reveals that addition of 3% DIO additive in CB solvent improve the morphology (lower charge carrier recombination and better metal/organic semiconductor interface) and provide uniform interpenetrating networks in PBDTTT-EFT:PC71BM blend active layer.In this work, we have fabricated highly efficient polymer solar cells based on the blend of PBDTTT-EFT:PC71BM in the inverted device configuration. By using low temperature processed zinc oxide (ZnO) nanoparticles as an electron-transport layer (ETL) and 1,8-diiodooctane (DIO) as additive in chlorobenzene (CB) solvent we have achieved PCE of 9.43% with an excellent short-circuit current density (Jsc) of 17.6 mAcm−2, open circuit voltage (Voc) of 0.80 V and fill factor (FF) of 0.67. These results reveals that addition of 3% DIO additive in CB solvent improve the morphology (lower charge carrier recombination and better metal/organic semiconductor interface) and provide uniform interpenetrating networks in PBDTTT-EFT:PC71BM blend active layer.