Temperature-dependent Current Density Voltage Research Articles

Origin of breakdown mechanism in multicrystalline silicon solar cells

The local breakdown behavior of multicrystalline silicon solar cells occurring at reverse bias voltages of −10 V has been investigated by means of electroluminescence images and temperature dependent current density-voltage (J-V) measurements. Identification of temperature coefficient of breakdown current indicates that Zener effect is the dominating mechanism of the local breakdown (so-called type II breakdown). Investigations of the carrier transport mechanism under forward bias voltage suggest that there exist a large amount of defects in depletion region. The origin of type II breakdown is attributed to the defects in depletion region.

Experimental Analysis of Majority Carrier Transport Processes at Heterointerfaces in Photovoltaic Devices

The transport processes of majority carriers through potential barriers at heterointerface layers of GaAs solar cell structures are experimentally analyzed by optical-injection-dependent and temperature-dependent current–density voltage (J–V) measurements. It is shown that the influence of front-surface-field and back-surface-field layers on majority carrier transport mechanisms is most pronounced in the J--V characteristics when high-concentration or low-temperature operating conditions are concerned. A method to determine the effective majority carrier potential barrier height at heterointerfaces is described and exemplified at GaAs solar cells structures. Discussion is provided on how a significant improvement of the majority carrier flow at heterointerfaces is achievable by modification of the doping concentration profiles of the solar cell structure. The results are also applicable to other optoelectronic devices such as light-emitting diodes or detectors.

A comparative investigation of trap-limited hole transport properties in organic bulk heterojunctions

We have investigated the bulk hole transport properties of copper phthalocyanine (CuPc):fullerene (C60) and zinc phthalocyanine (ZnPc):C60 bulk heterojunctions by analyzing thickness- and temperature-dependent current density–voltage (J–V) characteristics in hole-only device configurations, i.e. indium-tin-oxide (ITO)/poly(ethylene-dioxythiophene):polystyrenesulphonate (PEDOT:PSS)/CuPc: C60 or ZnPc:C60/molybdenum oxide (MoO3)/Al. It has been found that the hole transport is governed by a space-charge-limited current (SCLC) model in the presence of exponentially distributed traps within the bandgap. The hole mobility of CuPc:C60 mixture (1 × 10−5 cm2 V−1 s−1) is higher than that of ZnPc:C60 mixture (6.2 × 10−6 cm2 V−1 s−1), which can be ascribed to the differences of the characteristic trap energy and the total density of traps in both bulk heterojunctions. These results indicate that the SCLC method is applicable for studying the transport properties in organic bulk heterojunction.

Bias and temperature dependent charge transport in solution-processed small molecular mixed single layer organic light emitting devices

The authors investigate bias and temperature dependent current density-voltage (J-V) characteristics in solution-processed small molecular mixed single layer organic light emitting devices using Au/MoO3 as hole and Al as electron injection electrode. Hole and electron injections are primarily ascribed to the Schottky thermionic emission mechanism. However, at high field of >9×105 V cm−1, hole transport is found to be bulk trapped corresponding to space charge limited current with an exponential distribution of traps. The bulk trap density, about 1018 cm−3 in mixed organic layer, is evaluated by the differential method.

Interface Characterization and Electrical Transport Mechanisms in a-Si:H/c-Si Heterojunction Solar Cells

The fabrication of amorphous silicon/crystalline silicon (a-Si:H/c-Si) heterojunction solar cell and an understanding of the fundamental conduction mechanism in the device are presented. In the first part, the effect of intrinsic amorphous silicon [a-Si:H(i)] layer thickness on the performance of a-Si:H/c-Si solar cells has been studied. The thickness of a-Si:H(i) layer formed on n-type c-Si substrate was controlled accurately with spectroscopy ellipsometry (SE). Based on SE results, we discuss the influence of the a-Si:H(i) thickness on the interface quality and thereby cell performance. Then, in the latter part, we present the temperature-dependent current density–voltage curves, in the dark, in order to elucidate the dominant transport mechanisms in a-Si:H/c-Si heterojunction solar cells with and without incorporation of a-Si:H(i) layers. Finally, using optimum design considerations, we obtained a solar cell efficiency of 17.43%.

Numerical and experimental indication of thermally activated tunneling transport in CIS monograin layer solar cells

The purpose of this work was to build a numerical model of thermally activated tunneling transport by upgrading the drift-diffusion transport model in one-dimensional semiconductor simulator ASPIN, and to identify the current limiting mechanisms of the CIS monograin layer solar cells. The superposition of the classical drift-diffusion transport and the semi-classical thermionic-field transport is applied across the whole solar cell structure. The implemented model correctly predicts the shapes of temperature dependent current density–voltage characteristics and the temperature dependence of the photogenerated current density at the short-circuit condition in the range from 320 K down to 160 K.

Charge transport in poly(p-phenylene vinylene) light-emitting diodes

Abstract Since the discovery of electroluminescence in conjugated polymers it has been recognized that charge transport is a key ingredient for the efficiency of the polymer light-emitting diodes (PLEDs). This review focuses on the charge transport properties of these materials. From temperature dependent current density–voltage characteristics it has been obtained that the hole transport in poly(dialkoxy-p-phenylene vinylene) (PPV) is governed by a combination of space-charge effects and a field- and temperature-dependent mobility. The origin of the hole mobility, which seems to be generic for a large class of disordered materials, arises from hopping in a system with both energetic and structural disorder. The response time of PPV-based PLEDs is governed by the dispersive transport of holes towards the cathode. Based on the results of the electron- and hole-transport a device model for PLEDs is proposed in which the light generation is due to bimolecular recombination between the injected electrons and holes. The unbalanced electron and hole transport gives rise to a bias dependent efficiency. By comparison with experiment it is found that the bimolecular recombination process is of the Langevin-type, in which the rate-limiting step is the diffusion of electrons and holes towards each other. The occurrence of Langevin recombination explains why the conversion efficiency of current into light of a PLED is temperature independent. The understanding of the device operation of PLEDs indicates directions for further improvement of the performance.