Manisha Bajpai

EPR and optical study of Mn2+ doped ammonium tartrate single crystals.

EPR study of Mn2+ doped ammonium tartrate single crystals is carried out at room temperature. The spin Hamiltonian parameters are: gx=1.9225+/-0.0002, gy=1.9554+/-0.0002, gz=2.1258+/-0.0002, A=(78+/-2) x 10(-4) cm(-1), B=(75+/-2) x 10(-4) cm(-1), D=(191+/-2) x 10(-4) cm(-1), E=(61+/-2) x 10(-4) cm(-1) and a=(22+/-1) x 10(-4) cm(-1) for site I and gx=1.9235+/-0.0002, gy=1.9574+/-0.0002, gz=2.0664+/-0.0002, A=(78+/-2) x 10(-4) cm(-1), B=(75+/-2) x 10(-4) cm(-1), D=(180+/-2) x 10(-4) cm(-1), E=(57+/-2) x 10(-4) cm(-1) and a=(22+/-1) x 10(-4) cm(-1) for site II, respectively. The observed optical bands are fitted with inter-electronic repulsion parameters (B and C), crystal field parameter (Dq) and Trees correction (alpha) and the values found are B=752, C=2438, Dq=765 and alpha=76 cm(-1). The data obtained are further used to discuss the surrounding crystal field and the nature of metal-ligand bonding in the crystal.

Incorporation of liquid crystalline triphenylene derivative in bulk heterojunction solar cell with molybdenum oxide as buffer layer for improved efficiency

ABSTRACT We report efficient bulk heterojunction solar cells fabricated by inserting a discotic triphenylene derivative into poly (3-hexylthiophene): [6, 6]- phenyl-C61-butyric acid methyl ester. A layer of molybdenum oxide was inserted between anode and active layer. Power conversion efficiency of 2.0% was achieved for these photovoltaic solar cells containing self-organised discotic liquid crystals in the active layer under one sun condition. The influence of varying the thickness of liquid crystal layer and annealing on these solar cells was also studied. Post annealing the bulk heterojunction devices with discotic liquid crystal layer of thickness 20 nm in them yielded an open circuit voltage of 0.41 V, short circuit current density of 17.0 mA cm−2, a Fill factor of 0.35 and power conversion efficiency of 2.5%. Graphical Abstract

Bulk heterojunction solar cells based on self-assembling disc-shaped liquid crystalline material

ABSTRACT In this article, effect of addition of disc-shaped liquid crystalline material, namely 2, 3, 6, 7, 10, 11-hexabutyloxytriphenylene, in poly (3-hexylthiophene): [6, 6]-phenyl-C61-butyric acid methyl ester containing bulk heterojunction (BHJ) solar cells has been investigated. These disc-shaped molecules organise into ordered columnar hexagonal structures through intermolecular π − π interactions as monitored by polarised light optical microscopy. Current–voltage characteristics of the device prepared with liquid crystal layer exhibited a short-circuit current of 10.5 mA cm−2 and a fill factor of 35%. The resultant power conversion efficiency (PCE) was 1.54%. The influence of varying the thickness of liquid crystal layer and annealing on these solar cells was also studied. The short circuit current and PCE of 12.9 mA cm−2 and 2.3% was achieved for these BHJ solar cells containing self-organised discotic liquid crystals in the active layer under one sun condition after annealing. GRAPHICAL ABSTRACT

EPR and optical absorption studies of copper ions in diglycine calcium chloride tetrahydrate.

EPR study of copper ions in diglycine calcium chloride tetrahydrate (DGCCT), [(NH(2)CH(2)COOH)(2).CaCl(2).4H(2)O] single crystals at room temperature is carried out. The spin Hamiltonian parameters of copper ions are determined as: g(x)=2.0238+/-0.0002, g(y)=2.1122+/-0.0002, g(z)=2.2250+/-0.0002, A(x)=(83+/-2)x10(-4)cm(-1), A(y)=(86+/-2)x10(-4)cm(-1) and A(z)=(118+/-2)x10(-4)cm(-1). The optical study of the single crystals at room temperature is also done and the bands are assigned to d-d and charge transfer transitions. Using above data, the nature of bonding in the complex is discussed.

Review on Optical and Electrical Properties of Conducting Polymers

We reviewed optical and electrical properties of conjugated polymers. The charge transport models to describe the hole and electron transport mechanism are also included in the electrical properties of conjugated polymers. The effect of optical and electrical properties after doping is also indexed in this paper.

Bulk heterojunction solar cells made from carbazole copolymer and fullerene derivative with an inserted layer of discotic material with improved efficiency

ABSTRACT Bulk heterojunction photovoltaic cells based on composites of copolymer poly [N-90-hepta-decanyl-2,7-carbazole-alt-5,5-(40,70-di-2-thienyl-20,10,30-benzothiadiazole)] and the fullerene derivative [6,6]-phenyl C71-butyric acid methyl ester with an inserted layer of discotic liquid crystalline material (2, 3, 6, 7, 10, 11-hexabutyloxytriphenylene) between the interface of active layer and hole transporting layer has been reported. Different hole transporting layers deposited on indium tin oxide substrates such as poly (3,4-ethylenedioxythiophene)-poly (styrenesulphonate) or molybdenum trioxide has been used in these devices. All the devices with inserted discotic liquid crystal layer showed better performance than the reference cells. Power conversion efficiency of 5.14% was achieved for these photovoltaic solar cells containing self-organised discotic liquid crystal layer of 30 nm thickness under one sun condition which is substantial jump as compared to earlier reports. The mobility of holes in the discotic liquid crystal inserted devices was found to be of the order of 10–6 cm2 V–1 s–1 due to which high values of current density was achieved. The influence of varying the thickness of liquid crystal layer and annealing on the photovoltaic parameters of these devices was also studied. GRAPHICAL ABSTRACT

Effect of Plasmonic Enhancement of Light Absorption on the Efficiency of Polymer Solar Cell

We demonstrate the effect of insertion of Au nano clusters nano clusters(NCs) with various thickness on the power conversion efficiency (PCE) in bulk heterojunction polymer solar cells polymer solar cellbased on blended poly(3-hexylthiophene):[6, 6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) (Li et al., Nat Photo 6:205, [1]). The Au NCs were vacuum deposited on pre cleaned indium-tin-oxide (ITO) substrates prior to deposition of poly (3,4-ethylene dioxythiophene:poly (styrene sulfonate) (PEDOT:PSS) buffer layer. It has been found that both short-circuit current density and PCE increase after incorporating Au NCs between ITO/PEDOT:PSS interface. The PCE enhancement is attributed to the localized surface plasmonic excitation of Au NPs (Tada et al., Nat Mat 10:450, [2]). The method employed has great potential in future practical applications.

Effect of doping on the electron transport in polyfluorene

In this paper, electron transport of pure and DMC doped polyfluorne (PF) films have been studied at various doping concentrations. Pure films show space charge limited conduction with field and temperature dependent mobility. The J–V characteristics of doped PF were ohmic at low voltages due to thermally released carriers from dopant states. At higher voltages the current density increases nonlinearly due to field dependent mobility and carrier concentration thereby filling of tail states of HOMO of the host. The conductivity of doped fims were analyzed using the Unified Gaussian Disorder Model (UGDM). The carrier concentration obtained from the fitting show a non-linear dependence on doping concentration which may be due to a combined effect of thermally activated carrier generation and increased carrier mobility.

Enhanced Hole Transport in Polyfluorene Polymer by Using Hole Injection Layer

Hole transport in poly(9,9-dioctylfluorene) (PFO) are measured by performing current density- voltage (J-V) measurements as a function of temperatures. For the J–V measurements, F4TCNQ is used as hole injection layer (HIL). Two different devices of PFO polymer are fabricated F4TCNQ having device configuration ITO/PFO/Au (with interface modification) and ITO/PFO/F4TCNQ/Au (with interface modification) respectively. Since, F4TCNQ is evaporated on the top of PFO film so that the contacts are taken from Au.