A room‐temperature low‐cost TiS2 p‐type contact material is applied for the first time as the hole‐transporting material (HTM) in perovskite solar cells, with power conversion efficiencies surpassing 13.5%. Synthesized by a simple two‐step hot‐injection method, it presents a much lower price per m2 than octakis(4‐methoxyphenyl)‐9,9′‐spirospirobi[9H‐fluorene]‐2,2′,7,7′‐tetramine (spiro‐OMeTAD), 30 times lower in price ($0.046 for TiS2 and $1.36 for spiro‐OMeTAD at 13.54% efficiency), standing out over most of the reported HTM alternatives.

We have investigated the influence of perovskite morphology on slow and fast charge transport in the perovskite solar cells. Solar cells with different perovskite cuboid sizes (50-300 nm) have been fabricated using various methylammonium iodide concentrations. Both the low-frequency capacitance and hysteresis are maximum for the cell with the largest perovskite grains (300 nm). The low-frequency capacitance is about three orders of magnitude greater than the intermediate frequency capacitance, indicating the great role of ions on the slow responses and hysteresis. The measurement of open-circuit voltage decay indicates that for the large grains of 300 nm up to 70% of V remains across the cell, even after passing ∼40 s. Such a long time V decay demonstrates the large accumulation of the ions at the perovskite interfaces with electron and hole transport layers, which conduct slow redistribution of the charges after the light is turned off.

A simple and practical approach is introduced for the deposition of CuI as an inexpensive inorganic hole-transport material (HTM) for the fabrication of low cost perovskite solar cells (PSCs) by gas-solid phase transformation of Cu to CuI. The method provides a uniform and well-controlled CuI layer with large grains and good compactness that prevents the direct connection between the contact electrodes. Solar cells prepared with CuI as the HTM with Au electrodes displays an exceptionally high short-circuit current density of 32 mA cm(-2) , owing to an interfacial species formed between the perovskite and the Cu resulting in a long wavelength contribution to the incident photon-to-electron conversion efficiency (IPCE), and an overall power conversion efficiency (PCE) of 7.4 %. The growth of crystalline and uniform CuI on a low roughness perovskite layer leads to remarkably high charge extraction in the cells, which originates from the high hole mobility of CuI in addition to a large number of contact points between CuI and the perovskite layer. In addition, the solvent-free method has no damaging side effect on the perovskite layer, which makes it an appropriate method for large scale applications of CuI in perovskite solar cells.

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The synthesization of Cu2O thin films by electrodeposition for photoelectrochemical water splitting is reported. The synthesized Cu2O samples are annealed at different temperatures between 300 and 500 °C. The XRD analysis and SEM images indicate that the sample without annealing includes Cu2O grains with pyramid shape. With annealing to more than 300 °C, due to the oxidization of the sample, a thin layer of CuO appears on the original Cu2O film and the crystalline signatures of such CuO structure increase with annealing at higher temperatures. The photoelectrochemical measurements indicate that annealing pure Cu2O by more than 300 °C, remarkably increases the photocurrent achieved from this photocathode. The effect is accompanied with considerable improvement of chemical stability of the original Cu2O electrode during water splitting. Such protection effect, which is originated from generation of CuO on the samples, increases with the annealing temperature up to 500 °C. However, the best photocurrent from the Cu2O/CuO composite is obtained from the annealing temperature of about 400 °C. The results of impedance analysis of various annealed samples indicate that annealing at a higher temperature, better charge transfer occurs both at the interface of photocathode/electrolyte and inside the photocathode.