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The degradation of methyl-ammonium lead iodide (MAPbI3) upon exposure to air is a potentially limiting effect for large scale MAPbI3 photovoltaic production. Here, we report a systematic study on effects of air-exposure on the structural and optical properties of MAPbI3 thin films. The X-ray diffraction studies indicate a shrinking volume of MAPbI3 upon air-exposure as the material decomposes back to its precursors, methyl amine (CH3NH2) and lead iodide (PbI2). However, the photoluminescence (PL) yield and carrier lifetime measured with time-resolved photoluminescence, show an increasing trend upon air-exposure. These phenomena can be explained by self-passivation of MAPbI3 grains by PbI2 layer that reduces the number of non-radiative recombination centres at the grain boundaries. However, this process is not self-limiting and it eventually leads to a film that has completely reverted back to its precursor state. It is shown that this conversion of MAPbI3 film back to its precursors is also accelerated by exposure to laser illumination. Furthermore, we report unusual variation of PL intensity on a shorter time scale of a few seconds in all the films used for the experiment. The variations are found to follow different trends in the encapsulated samples as compared to the un-encapsulated samples. We propose that the decomposition followed by the ionic diffusion through film is responsible for such unusual behaviours.

We report the growth of p -type As-doped, Cd-rich CdTe single crystals using metallic Cd as the solvent in the traveling-heater method. We investigate the growth process from Cd solution in terms of the solid-liquid interface shape and the effects of As incorporation on p -type doping. The resulting CdTe crystals have Cd-rich composition which enhances p -type doping. The As doping efficacy was measured for As concentrations by the combination of inductively coupled plasma mass spectrometry, capacitance-voltage measurements. The p -type doping concentration varied from 6 × 10 15 to 8 × 10 16 cm −3 with increasing As concentration, with an apparent doping limit just below 10 17 cm −3 .

One industrially relevant fabrication method for CuInSe2 absorber layers begins with electrodeposition, which is highly resource efficient and easily up-scalable, followed by a high temperature annealing step. Commonly a furnace is used for annealing, although it is possible to reduce the duration of this step by 2–3 orders of magnitude using laser heating. Past work demonstrated that rastering a 1064 nm, continuous wave, neodymium-doped yttrium aluminium garnet laser beam over an electrodeposited precursor film with 1 s dwell time, promoted CuInSe2 formation, grain growth, and gave a photovoltaic device with 1.6% power conversion efficiency. However, this device showed inhomogeneous current collection correlating approximately to the Gaussian flux profile of the laser beam. This work demonstrates how deviations in the incident laser flux on the precursor lead to local temperature variation in the film. The temperature affects the rates of atomic diffusion, grain growth and chemical reactions, with the hottest region having the largest crystallites and a stoichiometric and constant composition through the film depth. Spatially resolved photoluminescence yield shows a positive correlation to the temperature profile caused by the Gaussian flux. It is expected that with a homogeneous laser beam flux, spatial variations in absorber layer properties would be eliminated, leading to uniform device properties.