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In this paper, we investigate the electrical hole transport properties of an organic/inorganic heterostructure consisting of a thin organic film, that combines hole and electron conducting molecules around a bridging Zn-atom, deposited on top of an n-type crystalline silicon substrate. Current-voltage characteristics and capacitance voltage measurements have been used for the determination of the organic layer dielectric and hole conduction parameters.

A theoretical model, combining trapping/detrapping and recombination mechanisms, is formulated to explain the origin of random current fluctuations in silicon-based solar cells. In this framework, the comparison between dark and photo-induced noise allows the determination of important electronic parameters of the defect states. A detailed analysis of the electric noise, at different temperatures and for different illumination levels, is reported for crystalline silicon-based solar cells, in the pristine form and after artificial degradation with high energy protons. The evolution of the dominating defect properties is studied through noise spectroscopy.

The radiation hardness of CH3 NH3 PbI3 -based solar cells is evaluated from in situ measurements during high-energy proton irradiation. These organic-inorganic perovskites exhibit radiation hardness and withstand proton doses that exceed the damage threshold of crystalline silicon by almost 3 orders of magnitude. Moreover, after termination of the proton irradiation, a self-healing process of the solar cells commences.

Some commercially available solar panels with very high efficiencies for terrestrial photovoltaic applications are based on the amorphous silicon on crystalline silicon material system. This type of heterostructure has more than 40 years' old history. The early development of the technology and the results, obtained in the last years with this type of solar cell are reviewed. In particular it is demonstrated why the physical understanding of the interface properties and band-structure was important for the development of high efficiency solar cells.

Organic/inorganic heterojunctions have been fabricated by spin-coating of an oxadiazole based polyether on top of either n-type or p-type crystalline silicon substrates. The prepared heterodiodes showed good rectification. During current-voltage measurements sharp current switching effects have been observed in the reverse bias characteristics for both types of heterodiodes. In particular a very stable hysteresis in the reverse characteristics of the polyether/n-type crystalline silicon has been measured at applied voltages below 1V. The application of this heterodiode as electrical memory with an on/off-ratio of about 2 orders of magnitude has been demonstrated (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The decay of optically generated excess charge carriers at the heterointerface between crystalline silicon and amorphous silicon has been monitored in situ during plasma deposition of the amorphous layer. A dramatic increase in the interface recombination rate is seen instantly when the silane plasma is ignited. In a later stage of amorphous layer deposition, the recombination rate decreases. This interface passivation depends strongly on the substrate temperature and is more efficient at higher temperature and in the presence of silane plasma. The effect is not due to a change in the band bending at the heterointerface.

The damage induced by hydrogen and helium plasmas at the surface of crystalline silicon has been monitored in situ by time‐resolved microwave conductivity and by spectroscopic ellipsometry measurements. Both plasma treatments increase the decay rate of the optically generated excess charge carriers and decrease the amplitude of the microwave reflection transients. While for the helium plasma a high density of electronic defects is created immediately after plasma ignition, a continuously increasing number of recombination centers is observed in the case of the hydrogen plasma exposure. In support of the transient microwave measurements, the analysis of the spectroscopic ellipsometry measurements reveals the creation of a damaged surface layer, which in the case of the helium plasma exposure has a high and in the case of the hydrogen plasma a low fraction of amorphous silicon. This can be explained by the different nature of the processes involved in the interaction of hydrogen (chemical) and helium (physi...

During removal of amorphous silicon films deposited on crystalline silicon substrates by dry etching in a hydrogen plasma the kinetics of mobile excess charge carriers have been followed by measuring the change of the microwave reflection after laser pulse illumination. Following the amplitude of the measured transient signals the thickness of the remaining amorphous silicon film can be determined and the decay in the nanosecond time range yields information about the defect density of the substrate surface. The impact of the plasma process on the surface recombination is shown and a criterion for endpoint detection is given in the case of a‐Si:H removal from crystalline silicon covered with a SiO2 layer.

Irradiation of unsupported samples of hydrogenated amorphous silicon below 100 K with 360-MeV Xe ions results in macroscopically visible changes in sample dimensions. These changes have two different causes. Formation and growth of cavities lead to an isotropic increase of the specimen dimensions and to a drastic decrease of the mass density. Simultaneously plastic flow occurs, which produces additional but anisotropic changes of the specimen dimensions. The dimensions perpendicular to the beam grow whereas the dimension parallel to the ion beam shrinks. Neither effect saturates in the investigated fluence range (Φt< 1014Xe/cm2) and both are absent in crystalline silicon. The effects are most likely provoked by electronic excitations and/or ionizations in the wake of the fast ions. With respect to plastic flow,a–Si:H behaves like metallic and oxide glasses. Formation of cavities and their growth, however, seem to occur only in tetrahedrally coordinated solids.

The dispersion of conventional amorphous silicon (a-Si:H)/crystalline silicon (c-Si) heterojunction solar cells shows a single time constant behavior. However, when a multicrystalline substrate is used, an additional "hump" appears in the C-f and R-f curves. A possible explanation by the introduction of a second time constant fails. As an alternative, interface states are considered as the reason of the hump. Thus, an equivalent circuit is established which is used to extract the parallel conductance and capacitance caused by the interface states. A bell-shaped conductance (normalized to frequency) and a step-shaped capacitance appear as predicted by Shockley-Hall-Read theory. The evaluation can be further improved by application of the statistical model (assumption of a fluctuating surface potential). The final data are a surface state density Dit of 2.3 1012 V-1cm-2, a time constant tauit of 1.7 ms and a standard deviation a of 0.8

Measurements of the transient photoconductivity detected via the change in microwave reflection after laser pulse illumination have been performed during the exposure of crystalline silicon substrates to a pure silane, silane/helium, and pure helium plasma. In all cases, a similar increase of the surface recombination rate is detected immediately after plasma start. While the surface recombination remains high in the case of the pure helium plasma, a decrease of the interface recombination is observed for the pure silane and silane/helium plasma, related to the deposition of hydrogenated amorphous silicon.

The plasma-induced deposition of hydrogenated amorphous silicon on crystalline silicon substrates has been investigated in situ by contactless transient photoconductivity measurements. In the initial stage of the deposition process the signals reflect charge-carrier kinetics in the substrate with the surface recombination rate modified by the deposition process. In the final stage the signal is dominated by mobile electrons in the film deposited. Between these extrema an additional contribution of excess charge carriers optically induced in the amorphous silicon film and transported to the substrate is observed. It is shown that this transport is inhibited by a high defect density in the film deposited and by a highly defective interface

In situ measurements of the transient photoconductivity during the deposition of amorphous silicon films on single-crystalline silicon substrates indicate a drastic increase of the surface recombination at the interface immediately after the start of the plasma discharge. This can be attributed to an initial damage of the substrate surface by impact of plasma-induced species on the silicon surface. The subsequent deposition of amorphous silicon films leads to a quenching of this plasma-induced surface recombination where this quenching process is faster at higher deposition temperatures. This passivation process is attributed to an interfacial relaxation occurring under influence of plasma-induced species even at an appreciable thickness of the a-Si:H film deposited. It is proposed that this process is an aspect of a general structure relaxation process in the material.

The signal of the Transient Microwave Detected Photoconductivity after laser pulse illumination is followed during the PECVD growth of intrinsic amorphous silicon on top of crystalline silicon (c-Si) substrates. Depending on the thickness of the amorphous layer the observed phototransients can be assigned to the excess charge carriers in different regions of the so grown heterojunction. For thin a-Si:H layers the signal amplitude decreases exponentially with deposition time. In the case of thick amorphous silicon the signal reflects only the properties of the amorphous silicon and the signal amplitude is constant. In an intermediate range a large contribution of charge carriers absorbed in the a-Si:H and subsequently transported to the crystalline part of the heterostructure to the measured signal can be observed. Due to their much higher mobility in the crystalline layer these excess charge carriers become visible only after reaching the crystalline silicon. This leads to the observed delay of the TRMC signal amplitude relative to the exciting laser pulse. The experiments show, however, that this charge carrier transfer takes place only in the case of a low defect a-Si:H layer to a measurable extent and is suppressed by the low carrier mobility in highly defective a-Si:H deposited at lower substrate temperatures.

The applicability of amorphous silicon/crystalline silicon (a-Si:H/c-Si) heterojunction solar cells for their use in space environment was tested. The cells were subject to proton irradiation at energies between 0.8 and 4 MeV. The optical and electrical parameters were measured. The diffusion lengths, L-D(,) were deduced from the internal quantum efficiency. A plot of 1/L-D(2) vs the applied doses yielded the damage constant. This procedure was repeated for the energy range of 0.8-4 MeV. The damage constants were lower or comparable to those of diffused solar cells. As in the case of conventional solar cells a maximum was found for an energy of 1.7 MeV. The spectral response calculated by means of the AFORSHET simulation program was fitted to the experimental data, using an inhomogeneous defect distribution within the crystalline silicon substrate after irradiation. The defect density used as a fit parameter was proportional to the implanted proton dose. (c) 2006 The Electrochemical Society.

Hydrogenerated amorphous silicon/crystalline silicon (a-Si:H/c-Si) solar cells with areas of 1 X 1 cm are produced by deposition of a-Si:H and indium-tin-oxide (ITO) on 3-in. wafers. Three types of samples have been prepared for admittance measurements, differing in the way how the effective area is defined. The measurement geometry is either defined by cutting, by etching the ITO layer outside the 1 cm 2 active area, or by etching the ITO and the a-Si:H outside the active area. Admittance measurements reveal that the lateral conductivity of the ITO is high enough up to a frequency of 1 MHz to ensure a lateral equipotential surface. A simple equivalent network consisting of a parallel resistor-capacitor branch in series to a second resistor controls the cut sample. For the sample with just ITO layer etching, the effects of a lateral channel due to the a-Si:H layer have to be included. The finite dimensions of the sample modify the low-pass character of the channel. The sample with ITO and a-Si:H layer etching delivers the best measurement conditions. In all three cases the dispersion allows the surface doping level of the substrate to be extracted from the CV characteristics measured at 1 MHz.

Transient photoconductivity measurements have been performed in situ during plasma-enhanced chemical vapor deposition of amorphous hydrogenated silicon by a contactless method that uses the change of the microwave reflection after laser pulse illumination. Through the use of the interference pattern of the amplitude of the transients of microwave reflection during the layer growth, the actual thickness of the amorphous film can be determined. In the case of crystalline silicon substrates, the change in the light absorption in the substrate modified by the growth of the amorphous layer is measured directly. An example of the optimization of antireflective layers on crystalline silicon substrates is shown. A good agreement is found between the experimental data and calculations of optical reflection and transmission on the multilayer structures.

It is shown that the deposition of a-Si:H films on c-Si wafers yields a reasonably passivated surface of the wafer. The passivation of the c-Si surface is better, if the a-Si:H film has better optoelectronic properties. Cleaning of the wafer surface deposition is required as it is shown for HF cleaning.

The transient photoconductivity decay rate is monitored on crystalline silicon samples in-situ during the heating of the samples up to 250°C and subsequent cooling by measuring the changes in the microwave reflection of the silicon sample following laser pulse illumination. An irreversible change of the excess charge carrier lifetime is found, showing a much slower decay after the first heating to 250°C. Subsequent thermal cycles show only a weak temperature dependence of the excess charge carrier decay rate at different temperatures. The strong dependence of this effect on the wavelength of the exciting laser indicates that the effect is caused by a modification of a near surface region of the crystalline silicon. The dependence of the signal amplitude on the measurement temperature is used to derive the temperature dependence of the sum of the electron and hole mobilities in the crystalline silicon. Wahrend des Heizens von kristallinem Silizium auf 250°C und anschliesendem Abkuhlen auf Raumtemperatur wird in-situ die uberschusladungstragerkinetik mittels Messung der transienten Mikrowellenreflektion nach Laserpulsanregung verfolgt. Mit ansteigender Substrattemperatur wird wahrend des ersten Heizens ein kontinuierliches Anwachsen der Ladungstragerlebensdauer gefunden, wohingegen beim anschliesenden Abkuhlen nur eine geringe Temperaturabhangigkeit der Ladungstragerlebensdauer beobachtet wird. Die Abhangigkeit dieses irreversiblen Prozesses von der Wellenlange des anregenden Lichtes deutet auf eine Modifikation der Oberflache des kristallinen Siliziums hin. Des weiteren wird mittels der Messung der Amplitude des transienten Mikrowellenreflektionssignals wahrend des Abkuhlens die Temperaturabhangigkeit der Summe von Elektronen- und Locherbeweglichkeit bestimmt.