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An approach to evaluate the microwave-detected photoconductance decay (MWPCD) is developed, which allows to extract the minority carrier lifetime as a function of the excess carrier density from a single MWPCD measurement. The method is shown to be applicable to thin (w≲200 μm) silicon wafers with low minority carrier recombination at the surfaces and bulk lifetimes in the range of about 1–100 μs. Comparison of the MWPCD results with minority carrier lifetime measurements using the quasi-steady-state photoconductance method reveals very good agreement between both types of measurement. Only when the photoconductance exceeds 30% of the dark conductivity, is a deviation observed, because then the MWPCD signal is no longer directly proportional to the excess carrier density. Minority carrier trapping is found to affect the MWPCD signal only in the tail of the measured photoconductance decay. The evaluation method is used to map the interstitial iron content with high spatial resolution, as well as to determine the minority carrier trap density. An excellent agreement between numerical simulation and measured MWPCD signal is found revealing the assumptions made for the evaluation approach to be valid. This evaluation of the MWPCD measurement is well suited to characterize silicon of low purity and low crystalline quality, which is often employed to solar cells with high spatial resolution.

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We observe variable-range hopping conduction in thermal admittance spectroscopy and develop a method to evaluate the signal under this condition. As a relevant example of demonstration we employ Cu(In,Ga)(Se,S)2 thin-film solar cells and show that the fundamental N1 signal, which has been discussed for more than a decade in terms of minority carrier traps, does not display trap parameters, but is generated by the freezing-out of carrier mobility with decreasing temperature when hopping conduction prevails. This effect offers a new approach to carrier hopping and to semiconductors suffering from small mobility.

Temperature and power dependent photoluminescence (PL) measurements were employed in order to study defects in close-space-sublimation grown polycrystalline cadmium telluride layers that had been activated with different chlorine containing compounds. The samples were either measured as-grown or after thermal treatment in an oxygen containing ambient with and without the chlorine containing compounds such as cadmium chloride, hydrochloric acid, and sodium chloride. The as-grown sample is discussed in detail, in order to then demonstrate the changes in the PL spectra induced by the postdeposition treatments. A deep level transition at 1.32 eV was observed in the as-grown sample which can be correlated with cadmium vacancies. Due to postdeposition treatments this deep level transition disappears and a broad band correlated with A-centers arises instead at about 1.43 eV. Another transition band at 1.479 eV in the as-grown sample is not influenced by any postdeposition treatment. Furthermore, by processing solar cells out of the respective samples, the PL results can be related to the solar cell parameters.

We investigate Cu–In thin films used as precursors for the production of CuInS2 and Se2 solar-cell absorber material via reactive annealing. The films are produced by coevaporation of Cu and In onto glass substrates and are characterized by means of Rutherford backscattering and x-ray diffraction (XRD). The interplay of phase composition, morphology, and surface topography is studied as a function of chemical composition, substrate temperature, and annealing processes. The analysis of the XRD data is based on known crystallographic data for the phases Cu7In3 (δ phase), Cu16In9 (η′ phase), Cu11In9, and In. Refined crystallographic data for CuIn2 are presented, and the low-temperature modification of Cu16In9 (η-phase) is investigated by means of bulk powder samples. These data and the inclusion of texture effects allow us to perform a complete RIETVELD type analysis of the Cu–In precursors. It is shown that, in contrast to sequentially evaporated films, all known Cu–In equilibrium phases can be formed during film deposition. These are Cu7In3, Cu16In9, Cu11In9, and CuIn2. Moreover, it is found that single-phase films of all these phases can be produced. Film roughness is shown to increase with deposition temperature and In content. The results presented offer new prospects for sulfurization and selenization processes in solar-cell production.

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