G.D. Sharma

Organic photovoltaic solar cells based on some pure and sensitized dyes

Organic photovoltaic solar cells based on metal-dye or sensitized dye-SnO2 junctions are formed. The electrical and photovoltaic characteristics of these Schottky junctions have been studied on two pure and sensitized dyes (Eriochrome Blue Black B and Rodamine B). From the photovoltaic action spectra the active region responsible for electric power generation was found to be confined to the SnO2-dye interface. The effect of sensitization, electrode material and intensity on photovoltaic and electrical parameters has also been discussed in detail. Finally theC-V characteristics are discussed in detail.

Charge transfer and photogeneration process in device consisting of safranine O dye and TiO2 nano-particles

Abstract We have studied the effect of titanium dioxide (TiO 2 ) nano-particles on charge transfer processes in safranine O (SAF) dye photovoltaic device. The photoconductivity is increased by two orders and a sharp saturation is also observed. The device shows a sharp saturation in photocurrent in forward bias which indicates that exciton diffusion and dissociation at the TiO 2 interface, due the existence of internal electric field is dominant process for the collection of charge. The value of diode quality factor has been calculated also by fitting the experimental results with modified Shockley equation. The internal electric field is mainly due to the asymmetry between the work functions of the materials. Electron injection from the excited state of dye on illumination, into the conduction band of TiO 2 is followed by subsequent hole transfer from the photooxidized dye to the collecting Al electrode, regenerating the dyes original ground state. The charge transfer and photogeneration process in device have been discussed on the basis of current–voltage characteristics and photoaction action spectra of the device.

Studies on electrical and photoelectrical behaviour of ITO/ArV/In Schottky barrier device

Abstract The electrical and photoelectrical properties of aryl viologen (ArV), chemically known as 1,1′-diphenyl-4,4′-bipyridinium dichloride, in the form of thin film, sandwiched between ITO and In electrode were studied. The current–voltage ( J – V ) characteristics in dark show the rectification effect due to the formation of Schottky barrier at In–ArV interface. The diode quality factor of the device, greater than unity, indicates the recombination of electron-hole in depletion region. Ohmic conduction in low voltage range and space charge limited conduction (SCLC) controlled by an exponential distribution of traps above the valence band edge, for higher voltage region have been observed. Various electrical parameters were calculated from the analysis of J – V and capacitance–voltage ( C – V ) characteristics at different temperatures and discussed in details. At higher frequencies, the device exhibit voltage independent capacitance, which is explained in terms of the extremely slow kinetics of space charge and low mobility of charge carriers. The photoaction spectra of the device and absorption spectra of the ArV thin film reveal that the fraction of light, which is absorbed near or within the diffusion length of exciton, is responsible for producing the free charge carriers. The photovoltaic parameters were calculated from the J – V characteristics under illumination through ITO and discussed in detail.

Photocarriers generation process and photovoltaic effect in PPHT thin film Schottky barrier devices

Abstract Photogeneration process and photovoltaic effect of Al/poly(3-phenylhydrazone thiophene) (PPHT)/ITO and In/PPHT/ITO sandwich devices were investigated by measuring steady state photocurrent resulting from illuminating through the ITO electrode. From the comparison of photoaction spectra of the device with the absorption spectra of the PPHT layer, it was observed that PPHT forms Schottky barrier with In and Al and ohmic contact with ITO. The voltage dependence of the photocurrent in the vicinity of V bi was measured at 1 mW/cm 2 of the incident illumination to give the open circuit voltage ( V oc ) and short circuit photocurrent ( J sc ). The photoaction spectra of the device also suggest that only light absorbed near the blocking contact, i.e., at Al/PPHT, In/PPHT is effective in producing carriers for external circuit. The dependence of the short circuit photocurrent on the illumination intensity was also described in detail. Various photovoltaic parameter was also calculated from the current–voltage ( J – V ) characteristics of the open device under illumination through ITO.

Electrical properties of pure, doped and sensitized organic dye films

Abstract There has been a growing technological interest in the electrical properties of thin films of organic dyes. The present paper is an account of studies of electrical properties of some pure, sensitized and iodine doped dyes. The dyes studied are (i) Eriochrome Black T (EBT), (ii) Eriochrome Blue Black B (EBBB), (iii) crystal violet (CV) and Rhodamine B (RB). The object of this work was to investigate the feasibility of fabricating an organic dye solar cell. Thin films of the organic dyes were made by solution casting. The thin film samples were studied in the sandwich configuration. The effects of sensitization and doping on the electrical parameters and the photovoltaic properties are discussed.

Characterization of ITO/ZnPc/CHR/In p-n junction-photovoltaic device using J–V, C–V and photoaction measurements

The electrical and photovoltaic properties of a newly designed two-layered photocell having the configuration ITO/ZnPc/CHR/In p-n junction were investigated. The rectification effect observed in the device is due to an energy barrier formed between the CHR and ZnPc layer. The depletion layer characteristics of the device were investigated by measuring the temperature variation of capacitance. These measurements indicate that a depletion layer of width 190 nm as well as potential barrier height of about 0.78 eV, decreases with temperature. The current–voltage characteristics of the device yield a barrier height of about 0.74 eV formed between ZnPc and CHR. The device showed a response to light over the whole visible region extending from 400 nm to 800 nm. The comparison of photoaction spectra with the absorption spectra also indicates the formation of an energy barrier between CHR and ZnPc. The dissociation of excitons induced by the built-in field potential existing between the CHR and ZnPc layers is responsible for photogeneration of the carriers. Various photovoltaic parameters were calculated and are discussed in detail.

Doping effect of viologen on rectification, charge transport processes and photovoltaic properties of furazano (3,4-b)piperazine thin film device

The electrical and photoelectrical properties of a sandwich junction device based on allyl viologen (AV)-doped furazano (3,4-b)piperazine (FP) having structure ln/AV : FP/ITO have been reported. A significant enhancement in the rectification, dark conductivity and photovoltaic response has been observed in AV-doped FP devices compared with undoped FP devices. The present communication deals with the charge transport mechanism and photogeneration process in ITO/AV doped FP/ln Schottky devices. The J–V characteristics recorded in the dark show a rectification effect due to the formation of a barrier at the AV-doped FP/ln interface. Impedance spectroscopy has been used to study the charge transport mechanism for AV-doped FP and its interface with ln. The bulk and junction resistance along with capacitance were determined by analyzing their contribution at an individual level. Doping imparts an improvement in photoresponse of FP as well as an abundance of photoexcited species at the interface.