Firoz Alam

ZnO anchored graphene hydrophobic nanocomposite-based bulk heterojunction solar cells showing enhanced short-circuit current

Hydrophobic and surfactant-free ZnO nanoparticles and ZnO decorated graphene nanocomposite (Z@G) with narrow and uniform size distribution were synthesized by a time-efficient microwave-assisted hydrothermal reaction that can be used specifically for application in hybrid photovoltaics. The synthesized ZnO nanoparticles and Z@G nanocomposite showed stable and clear dispersion in chloroform and methanol (with volume ratio of 9:1) and chloroform and ethanol (volume ratio 9:1). Being hydrophobic, these inorganic samples blend very well with organic polymer solution in chlorobenzene, which is a prerequisite to cast smooth and undisrupted film for hybrid solar cell application. The introduction of these hydrophobic nanoparticles into PCPDTBT:PCBM-based bulk-heterojunction polymer solar cells resulted in significant improvement in solar cell J–V characteristics with enhancement in open circuit voltage (VOC), short circuit current density (JSC) and thereby overall improvement in cell efficiency. With the optimization of the weight ratio of polymer, fullerene and synthesized ZnO nanoparticles/Z@G nanocomposite, the power conversion efficiencies 1.76% and 3.65% were achieved.

Effect of electric field on the spray deposited poly (3,4-ethylenedioxythiophene): poly(styrenesulfonate) layer and its use in organic solar cell

Spray process under different applied voltages (0 V to 700 V) is used for the deposition of poly (3, 4-ethylenedioxythiophene): poly (styrenesulfonate) (PEDOT:PSS) hole transport layer (HTL). The deposition of PEDOT:PSS film by spray process under the effect of electric field results in smoother film morphology, increase in conductivity and reduction in the sheet resistance. The improvement in surface morphology and conductivity enhancement of PEDOT: PSS films are the key to the improvement in the J–V characteristics of ITO/PEDOT:PSS/P3HT:PCBM/Al solar cell structures. The XPS peak height for PEDOT at 164.4 eV increased by 47% and that for PSS at 169.0 eV decreased by 30%, showing that the enhancement in the conductivity of the films deposited under electric field is due to the change in the PEDOT: PSS ratio. The organic solar cell using the electric field (created using 700 V) assisted spray deposited PEDOT:PSS film exhibit 42% and 69% improvement in the short circuit current density(Jsc) and power conve...

Role of zinc oxide and carbonaceous nanomaterials in non-fullerene-based polymer bulk heterojunction solar cells for improved cost-to-performance ratio

Cost-effective carbonaceous allotropes other than fullerene (i.e. carbon quantum dots or C-dots), ZnO nanoparticles and their nanocomposites were synthesized as alternatives to expensive fullerene in polymer-based bulk heterojunction solar cells. A facile microwave-assisted hydrothermal route was used to synthesize nanomaterials in a short time span along with inexpensive precursors to reduce the cost. Taking into account the cost-to-performance ratio, devices were fabricated in direct configuration as ITO/PEDOT:PSS/PFO-DBT:ZnO (or C-dots, Z@G, Z@Cdots)/Al followed by device optimization to obtain optimized device parameters. The devices exhibit significant short-circuit current density (Jsc), open-circuit voltage (Voc) and power conversion efficiency (PCE). The best power conversion efficiency of 3.9% with Jsc of 14.8 mA cm−2, Voc of 0.82 V and fill factor of 32% was obtained with Z@Cdots as acceptor at active layer concentration of 40 mg ml−1 and weight ratio of 1 : 1. In addition, the phase analysis of the active-layer interface demonstrates the better compatibility of the organic:organic phase (i.e. polymer:C-dots with a device PCE of 2.8%) as compared to the organic:inorganic phase (i.e. polymer:ZnO with a device PCE of 1.41%). Moreover, the best performance of the organic:hybrid phase (i.e. polymer:Z@Cdots with a device PCE of 3.9%) is due to the exploitation of properties of both organic and inorganic components on the same platform. C-dots as an acceptor give an overall power conversion efficiency of 2.8%, whereas Z@G resulted in an efficiency of 3.1%. A fullerene-based device gives an efficiency of 4.2% (just 0.3% more in comparison to Z@Cdots), but the difference in material cost is more than 50 times, which thus results in a significant improvement in the cost-to-performance ratio of a Z@Cdots-based device than a device using fullerene as an acceptor. Therefore, the developed carbonaceous nanomaterials act as potential acceptors in non-fullerene-based polymer solar cells for possible applications.

Photoluminescence study of oleic acid capped and hexanoic acid washed CdS quantum dots

The effects of oxygenic versus oxygen-free environment on the excitonic and defect emission of colloidal oleic acid (OA) capped and hexanoic acid washed CdS quantum dots (QDs) were studied using continuous photoluminescence (PL) measurements. In vacuum (∼10−3 mbar) OA capped CdS show 90% and 30% quenching of excitonic and defect emission intensity, respectively, whereas acid washed samples show 80% excitonic and 78% defect emission intensity quenching. It is also observed that the excitonic and defect emission intensities are fully recovered in air on cycling the air/vacuum pressure cycles. Our analysis suggests that due to high non-radiative recombination, both excitonic as well as defect emission intensity quenches. The low temperature PL study clearly shows that the enhancement in defect emission intensity for acid washed QDs is about three times higher than that of OA capped QDs, which is due to suppression of non-radiative recombination. Our work shows that emission can be controlled by modulating the degree of passivation ether by acid washing process or controlling the air/vacuum environment or both.

Optical Optimization of Solar Cells Having Extremely Thin SnS Layer on ZnO Nanowires

Use of non-toxic earth abundant materials is necessary for popularization of photovoltaic power generation. Here we have tried to optimize the dimensions of ZnO nanowires for maximum light absorption using Mie scattering . The light extinction was found maximum for ZnO nanowires of 140 nm. Approximations used for optimization and their validity have also been discussed. Here in this paper, formation of a semiconductor junction by depositing a thin layer of p type-SnS on n-type ZnO nanowires have also been reported.