The authors report on the formation of blisters during the atomic layer deposition of iridium using iridium acetylacetonate and oxygen precursors. Films deposited on fused silica substrates led to sparsely distributed large blisters while in the case of silicon with native oxide additional small blisters with a high density was observed. It is found that the formation of blisters is favored by a higher deposition temperature and a larger layer thickness. Postdeposition annealing did not have a significant effect on the formation of blisters. Finally, changing purge duration during the film growth allowed us to avoid blistering and evidenced that impurities released from the film in gas phase were responsible for the formation of blisters.

Diffractive mask-aligner lithography allows printing structures that have a sub-micrometer resolution by using non-contact mode. For such a purpose, masks are often designed to operate with monochromatic linearly polarized light, which is obtained by placing a spectral filter and a polarizer in the beam path. We propose here a mask design that includes a wire-grid polarizer (WGP) on the top side of a photo-mask and a diffractive element on the bottom one to print a 350 nm period grating by using a classical mask-aligner in proximity exposure mode. Linearly polarizing locally an unpolarized incident beam is only possible by using a WGP on the top side of the mask. This configuration opens the possibility to use different linear polarization orientation on a single mask and allows to print high resolution structures with different orientation within one exposure.

Two new processes for the atomic layer deposition of copper indium sulfide (CuInS2) based on the use of two different sets of precursors are reported. Metal chloride precursors (CuCl, InCl3) in combination with H2S imply relatively high deposition temperature (Tdep = 380 °C), and due to exchange reactions, CuInS2 stoechiometry was only achieved by depositing In2S3 layers on a CuxS film. However, the use of acac- metal precursors (Cu(acac)2, In(acac)3) allows the direct deposition of CuInS2 at temperature as low as 150 °C, involving in situ copper-reduction, exchange reaction and diffusion processes. The morphology, crystallographic structure, chemical composition and optical band gap of thin films were investigated using scanning electronic microscope, x-ray diffraction under grazing incidence conditions, x-ray fluorescence, energy dispersive spectrometry, secondary ion mass spectrometry, x-ray photoelectron spectroscopy and UV–vis spectroscopy. Films were implemented as ultra-thin absorbers in a typical CIS-solar cell architecture and allowed conversion efficiencies up to 2.8%.

We report in this paper the use of ZnInxSy films deposited by atomic layer deposition as cadmium free buffer layer in Cu(In,Ga)Se2 (CIGS) solar cells. Buffer layers with different In/(In + Zn) ratios over the whole composition range were prepared on glass substrate and characterized optically by transmission and reflection measurement and electrically by steady state photoconductivity and modulated photocurrent. CIGS solar cells were prepared with the different buffer layers and characterized. A compromise between the properties of In2S3 and ZnS was found for intermediate compositions as aimed for this study. Best efficiencies were obtained for intermediate composition (In/(In + Zn) close to 28 at. %) which also allows a higher open circuit voltage. Solar cell simulations allowed to point out the major role played by interface defect states in these devices.

The authors present the elaboration of zinc indium sulfide (ZnInxSy) thin films in the context of a cadmium-free buffer layer development for copper indium gallium diselenide photovoltaic solar cells. The films were deposited by atomic layer deposition (ALD) from ZnEt2 (DEZ), In(acac)3 (acac = acetylacetonate), and H2S at 200 °C. In situ growth kinetics studies were performed with the quartz crystal microbalance technique to determine the respective mass gain per cycle of ZnS and In2S3 layers, allowing determination of the atomic compositions of the ZnInxSy thin films to be expected if the deposition strictly follows the rule of mixtures. As the experimental atomic compositions of the ZnInxSy films differ significantly from this rule, a comprehensive study of the growth mechanism was performed to determine the nature of the side reactions. First, an exchange reaction between In2S3 and the Zn precursor was identified, though this process is not sufficient to account for the experimental data, and therefore, a second process which corresponds to the diffusion of species within the film was also found to take place. Ultimately, the atomic compositions of the ZnInxSy films can be explained by a rate-limited exchange reaction at the surface between DEZ and the In2S3 layer, combined with diffusion of the species in the whole film. More generally, such side reactions should be considered in ALD of multinary compounds, even at low temperature.

This study presents the effect of purge pulses conditions on the electrical and optical properties of zinc oxide films doped with aluminum and grown by ALD at low temperature (160 degrees C). Undoped ZnO films showed a clear improvement of the carrier concentration when purges were lengthened, which suggests that this purge lengthening causes a higher defect related doping. It was also showed that this purge lengthening leads to a further increase of the carrier concentration in the case of ZnO:Al films attributed to a better spatial repartition of the Al dopants in the film. The evolution of optical properties was also studied and compared to the electrical properties highlighting free carrier absorption and a Burstein-Moss shift. An abnormal modification of the optical properties was observed when the aluminum content in the film was increased. (C) 2012 Elsevier B. V. All rights reserved.

In this study, zinc indium sulfide (ZIS) thin films of different compositions ranging from pure In(2)S(3) to pure ZnS were synthesized by atomic layer chemical vapor deposition (ALCVD). In situ growth mechanism studies were carried out using the quartz crystal microbalance technique. They evidence preferential surface exchange reactions between indium and zinc ions during ALCVD pulses, which control the overall composition. Optical characterizations indicate a bandgap varying from 2.0 eV with indirect transition for In(2)S(3) to 3.6 eV with direct transition for ZnS. As deposited films present good crystallinity toward the two binary compounds which decreases at intermediate compositions. An amorphous phase appears in the material for the In/(In + Zn) ratio in the range 11-73 at % attributed to the conflict between the crystallographic structures of ZnS and In(2)S(3). Under thermal annealing treatments, grown films undergo crystallization processes. In particular, the thermal annealing of a sample with In/(In + Zn) similar to 73 at % leads to the formation of the crystalline phase ZnIn(2)S(4) with the presence of the crystallized In(2)S(3) phase.

The possibility to reach up to 14.7% efficiency with Cu(In,Ga)Se2 (CIGS) solar cell, using a cadmium free buffer layer (indium sulphide:In2S3) and an electrodeposited front contact (chloride doped ZnO:ZnO:Cl) is demonstrated in this article. This is the first time that costly gas phase deposition processes for ZnO, by high vacuum sputtering, can be replaced by an efficient low cost atmospheric technology, representing an important breakthrough in further cost reduction for photovoltaic application. In addition, the compatibility with cadmium free buffer layers brings this new approach at the cutting edge of strategic evolution of the CIGS technology. In this study the influences of the In2S3 buffer layer thickness, the presence of an intrinsic ZnO layer and a soft annealing treatment are studied. It is shown that the growth behavior of the electrodeposited ZnO:Cl is controlled by nucleation phenomena on different surfaces, with a unique morphology on indium sulphide. Finally the best performances have been achieved with a cell annealed at 150 °C under atmospheric conditions containing a very thin In2S3 layer (15 nm) but without intrinsic ZnO (CIGS/In2S3/ZnO:Cl).

It is currently possible to prepare Cd-free Cu(In,Ga)Se2-based solar cells with efficiencies similar or higher than their CdS references. In these cells, higher efficiencies are generally obtained from soft chemical-based techniques giving conformal depositions such as chemical bath deposition (CBD), ion layer gas reaction (ILGAR) or atomic layer deposition (ALD). However most of these devices are characterized by their pronounced transient behaviour. The aim of this paper is to compare these different chemical-based methods (CBD, ALD, ILGAR…) and to try to provide evidence for the dominant influence of the interface between the Cd-free buffer layer and the window layer on the performance and on the metastable electronic behaviour of these solar cells.

The aim of this thesis is to study the deposition of oxide and sulfide thin films using the atomic layer chemical vapor deposition (ALCVD) method. These materials are used to make copper indium gallium diselenide (CIGS) based thin film solar cells. First, indium sulfide, zinc sulfide and zinc indium sulfide thin films were deposited at 200 °C. The growth mechanisms of these materials were studied using the quartz crystal microbalance technique showing important desorption mechanisms taking place during purges and exchange reactions between diethylzinc and indium sulfide. Thin film characterizations and their use as buffer layers in solar cells showed that the material properties vary from the properties of indium sulfide to the one of zinc sulfide. The best solar cell reaches an efficiency of 11,2 % (reference buffer layer 12,3 %) and an open circuit voltage 15 mV higher than the one of the reference cell. Other materials based on zinc oxysulfide (Zn(O,S)) (Zn(O,S):In, Zn(O,S):Al) were studied as buffer layers but the performance reached were below those obtained with zinc indium sulfide buffer layers. Secondly, growth studies of zinc oxide (ZnO) and aluminum doped zinc oxide (ZnO:Al) thin films at 160 °C showed the influence of purge durations on the electrical properties of the layers. The comparison between ZnO:Al layers deposited by ALCVD and sputtered layers demonstrated that, when used as a window layer in solar cells, this material can reach equivalent or better performance. Finally, copper indium disulfide (CuInS2) thin films were obtained using a two stage process involving diffusion processes. A layer thinner than 300 nm was used as a solar cell absorber allowing an efficiency of 2,8 %.