Deposition conditions, optimization

Attempts have been made to deposit TIPS-pentacene from solution as the functional layer in a pentacene/C60 bilayer photovoltaic device. Careful optimization of deposition conditions, optimal concentration of mobile ion dopants, thermal postfabrication annealing, and the addition of an exciton-blocking layer yielded a device with a moderate white-light PCE of 0.52% [41]. Since TIPS-pentacene derivatives rapidly undergo a Diels-Alder reaction with fiillerene, the assembly of potentially more efficient bulk-heterojunction photovoltaic devices from TIPS-pentacene and fiillerene derivatives were not possible [42]. The energy levels of the TIPS-pentacene-PCBM adduct (PCBM is [6,6]-phenyl C61-butyric acid methyl ester) ineffectively supports the photoinduced charge transfer. 

It was reported recently [216] that optical-quality PbTe thin films can be directly electrodeposited onto n-type Si(lOO) substrates, without an intermediate buffer layer, from an acidic (pH 1) lead acetate, tellurite, stirred solution at 20 °C. SEM, EDX, and XRD analyses showed that in optimal deposition conditions the films were uniform, compact, and stoichiometric, made of fine, 50-100 nm in size, crystallites of a polycrystalline cubic structure, with a composition of 51.2 at.% Pb and 48.8 at.% Te. According to optical measurements, the band gap of the films was 0.31 eV and of a direct transition. Cyclic voltammetry indicated that the electrodeposition occurred via an induced co-deposition mechanism. 

The deposition conditions should be optimized to obtain approximately equal amounts of matrix and spreader-bar molecules on the surface [18,21]. Analysis of monolayers by near-edge X-ray absorption fine-structure spectroscopy. 

InAs, formed with 200 cycles. There are no indications of As in the XRD. From Figure 25, a plot of the (ahv)2 vs. energy, the bandgap was estimated to be 0.36 eV, in agreement with literature values. Bandgaps for the InAs deposits appear to be sensitive functions of a number of cycle variables. Several samples resulted in band gaps of closer to 0.44 eV. These blue shifts appear to result from smaller crystallites, nanoclusters, when the deposition conditions were not optimal. 

Further improvements in the design of the apparatus and optimization of the deposition conditions are expected to remove the remaining discrepancies. 

By careful optimization of the MAPLE deposition conditions (laser wavelength, repetition rate, solvent type, concentration, temperature, background gas and gas pressure), this process can occur without any significant chemical decomposition. When a substrate is positioned directly in the path of the plume, a coating starts to form from the evaporated organic molecules, while the volatile solvent molecules, which have very low sticking coefficients, are evacuated by the pump in the deposition chamber. 

Continued optimization of the deposition conditions led to efficiencies as high as 6.1% in p-i-n cells (1.19 cm2) by 1980 (Carlson, 1980a). An efficiency of 6.3% was reported later that year for a small (4.2-mm2) metal-insulator-semiconductor (MIS) device fabricated from a glow discharge in SiF4 and H2 (Madan et al., 1980) the film used in this MIS device was a silicon - hydrogen - fluorine alloy (a-Si H F). 

Other defect levels may arise from interactions between nearby dangling bonds that may form weak or stretched bonds, from dangling bonds on impurity atoms, and from weak bonds between silicon atoms and impurity atoms. The net result is that there is a distribution of defect levels throughout the band gap of a-Si H, and this distribution depends strongly on deposition conditions. Generally, good quality a-Si H has only been obtained after a comprehensive empirical optimization of the deposition conditions for a particular type of system. 

Subsequent preliminary comparative studies of the behavior of an SiC based layer on Ta, Mo, Ti and steel substrates showed that better mechanical stability was obtained with a coating deposited on tantalum. This element was consequently considered to make PFCVD deposit/interlayer/steel stacks. Tantalum can be produced by physical vapor deposition (PVD), at variable thickness, with reproducible morphology. Note that preparation by chemical vapor deposition with or without plasma assistance (CVD or PECVD) is possible at low temperature but would require an optimization study in order to be compatible with the deposition conditions of the silicon carbide layer, the aim being to increase the mechanical stability. 

A technology of Sr2FeMoObui (SFMO) nanosized films deposition by ion-beam sputtering is described. Optimization of deposition conditions on formation of structural ly-perfect SFMO double perovskite films is presented. Several problems arise with the use of the ion-beam sputtering method concerning the films inhomogeneity, the presence of multiple phases and Femo and Mope antistructural defects. It is shown that they are solved by means of complex selection of parameters substrate temperature, deposition rate and subsequent thermal processing. 

Thioacetamide, which is well established for the precipitation of ZnS in solutions, can be also used [68] in which case the films have been deposited from acidic solutions. The addition of urea has a beneficial effect on the adherence [68], Some attempts have been made to deposit ZnS by using thiosulfate-based solutions [16], As compared to CdS and PbS it appears that the deposition of ZnS films is not yet optimized and in addition presents some differences in the growth mechanism. This is illustrated by the lower activation energy values ( 20 kJ.rnol" ) which has been determined in the ammonia-thiourea-hydrazine process, which is more likely characteristic of a diffusion limited growth [69]. The deposition of indium sulfide has been also reported in acidic solutions using TA [52], along with a detailed study of the influence of the deposition conditions on the structural and optical properties of the films. 

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