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While the susceptibility of CH 3 NH 3 PbI 3 to water is well-documented, the influence of water on device performance is not well-understood. Herein, we use infrared spectroscopy to show that water infiltration into CH 3 NH 3 PbI 3 occurs much faster and at a humidity much lower than previously thought. We propose a molecular model in which water molecules have a strong effect on the hydrogen bonding between the methylammonium cations and the Pb−I cage. Furthermore, the exposure of CH 3 NH 3 PbI 3 to the ambient environment increases the photocurrent of films in lateral devices by more than 1 order of magnitude. The observed slow component in the photocurrent buildup indicates that the effect is associated with enhanced proton conduction when light is combined with water and oxygen exposure.

Efficient solar energy conversion with CuInS2 thin films is reported. The copper-rich p-type absorber is prepared by thermal coevaporation. A copper to indium ratio between 1.0 and 1.8 can be tolerated with small (≤10%) solar-to-electrical conversion losses. Copper excess phases (CuS) are removed chemically. The cell structure glass/Mo/p-CuInS2/n-CdS/n+-ZnO/Al delivers 10.2% at simulated AM 1.5 conditions. The device properties are discussed based on its energy band diagram.

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Perovskite solar cells based on (CH3NH3)Pb(I,Cl)3 have recently demonstrated rapidly increasing cell efficiencies. Here, we show progress identifying phases present during the growth of (CH3NH3)Pb(I,Cl)3 perovskite thin films with the vacuum-based coevaporation approach using two sources under varying deposition conditions. With in situ X-ray diffraction, crystalline phases can be identified and monitored in real time. For different (CH3NH3)I-to-PbCl2 flux ratios, two distinct (CH3NH3)Pb(IxCl(1-x))3 phases with high (x > 0.95) and with lower (x < 0.5) iodine content as well as a broad miscibility gap in-between were found. During post deposition annealing we observe recrystallization and preferential orientation effects and finally the decomposition of the perovskite film to PbI2 at temperatures above 200 °C.

The gallium gradient in Cu(In,Ga)Se2 (CIGS) layers, which forms during the two industrially relevant deposition routes, the sequential and co‐evaporation processes, plays a key role in the device performance of CIGS thin‐film modules. In this contribution, we present a comprehensive study on the formation, nature, and consequences of gallium gradients in CIGS solar cells. The formation of gallium gradients is analyzed in real time during a rapid selenization process by in situ X‐ray measurements. In addition, the gallium grading of a CIGS layer grown with an in‐line co‐evaporation process is analyzed by means of depth profiling with mass spectrometry. This gallium gradient of a real solar cell served as input data for device simulations. Depth‐dependent occurrence of lateral inhomogeneities on the µm scale in CIGS deposited by the co‐evaporation process was investigated by highly spatially resolved luminescence measurements on etched CIGS samples, which revealed a dependence of the optical bandgap, the quasi‐Fermi level splitting, transition levels, and the vertical gallium gradient. Transmission electron microscopy analyses of CIGS cross‐sections point to a difference in gallium content in the near surface region of neighboring grains. Migration barriers for a copper‐vacancy‐mediated indium and gallium diffusion in CuInSe2 and CuGaSe2 were calculated using density functional theory. The migration barrier for the InCu antisite in CuGaSe2 is significantly lower compared with the GaCu antisite in CuInSe2, which is in accordance with the experimentally observed Ga gradients in CIGS layers grown by co‐evaporation and selenization processes. Copyright © 2014 John Wiley & Sons, Ltd.

This paper deals with the analysis of the vibrational and crystallographic properties of CuInC 2 ͑C =S,Se͒ chalcogenides. Experimentally, evidence on the coexistence in epitaxial layers of domains with different crystalline order-corresponding to the equilibrium chalcopyrite ͑CH͒ and to CuAu ͑CA͒-has been obtained by cross section transmission electron microsopy ͑TEM͒ and high resolution TEM ͑HREM͒. Electron diffraction and HREM images give the crystalline relationship ͓110͔ CH ʈ ͓100͔ CA and ͑112͒ CH ʈ ͑011͒ CA , observing the existence of a ͑112͒ CH ʈ ͑001͒ CA interphase between different ordered domains. The vibrational properties of these polytypes have been investigated by Raman scattering. Raman scattering, in conjunction with XRD, has allowed identifying the presence of additional bands in the Raman spectra with vibrational modes of the CA ordered phase. In order to interpret these spectra, a valence field force model has been developed to calculate the zone-center vibrational modes of the CA structure for both CuInS 2 and CuInSe 2 compounds. The results of this calculation have led to the identification, in both cases, of the main additional band in the spectra with the total symmetric mode from the CuAu lattice. This identification is also supported by first-principles frozenphonon calculations. Finally, the defect structure at the interphase boundaries between different polymorphic domains has also been investigated.

In this paper, we treat diode currents caused by Shockley–Read–Hall recombination at the interface of pn heterojunctions. We are interested in the activation energy of the saturation current. To this end, we discriminate the cases of ΔEc,v≤0 and ΔEc,v&gt;0, where ΔEc,v is the band offset in the minority carrier band of the small band gap heteropartner, as well as the case of Fermi level pinning. Using analytical considerations, we find that the activation energy of the saturation current equals the band gap of the small band gap heteropartner for ΔEc,v&gt;0 but equals the interface band gap for ΔEc,v≤0. In the case of Fermi level pinning, the value of the potential barrier of the small band gap minority carrier equals the activation energy. These findings serve to discriminate different cases of interface recombination and to give information about the heterojunction energy band diagram.