The creation of a suitable inorganic colloidal nanocrystal ink for use in a scalable coating process is a key step in the development of low-cost solar cells. Here, we present a facile solution synthesis of chalcopyrite CuInSe 2 nanocrystals and demonstrate that inks based on these nanocrystals can be used to create simple solar cells, with our first cells exhibiting an efficiency of 3.2% under AM1.5 illumination. We also report the first solution synthesis of uniform hexagonal shaped single crystals CuInSe 2 nanorings by altering the synthesis parameter.

How low can you go? The lower limits of platinum loading, in the sub‐monolayer to monolayer range, have been explored for the hydrogen evolution reaction (HER). A low‐cost substrate material, tungsten monocarbide (see picture; W blue, C small gray spheres) is capable of supporting monolayer amounts of platinum (large blue‐gray spheres) to produce an electrocatalyst with the same HER activity as bulk platinum.

Polycrystalline thin film solar cells based on copper indium diselenide (CuInSe 2) and its alloys and cadmium telluride (CdTe) appear to be the most promising candidates for largescale application of photovoltaic energy conversion because they have shown laboratoryefficiencies in excess of 15%. Heterejunction devices with n-type cadmium sulfide (CdS) films show very low minority carrier recombination at the absorber grain boundaries and at the metallurgical interface which results in high quantum efficiencies. Open circuit voltages of these devices are relatively low owing to the recombination in the space charge region in the absorber. Further improvement in efficiency can be achieved by reducing this recombination current, especially in devices based on CuInSe 2 and its alloys. Low-cost manufacturing of modules requires better resolution of a number of other technical issues. For modules based on CuInSe 2 and its alloys, the role of Na and higher deposition rates on device performance need to be better understood. In addition, replacing the chemical bath deposition method for CdS film deposition with an equally effective, but more environmentally acceptable process are needed. For modules based on CdTe, more fundamental understanding of the effect of chloride/oxygen treatment and the development of more reproducible and manufacturable CdTe contacting schemes are necessary.

The properties and most successful methods for producing CuInSe2 films for solar-cell applications are reviewed and the production, analysis, and performance of photovoltaic devices based on CuInSe2 are discussed. The most successful methods for depositing thin CuInSe2 films for high-efficiency solar cells are three-source elemental evaporation and selenization of Cu/In layers in H2Se atmospheres. Devices based on CuInSe2 have achieved the highest conversion efficiencies for any nonepitaxial thin-film solar cell, 14.1% for a small cell and 10.4% (aperture efficiency) for a 3916-cm2 (4 sq. ft) device. Furthermore, high-efficiency devices have been produced by several groups and have shown no evidence of degradation of performance with time. The internal quantum efficiency is remarkably close to 100%, although various losses prevent making use of all of the generated carriers. The high performance results, in part, from the very-high-absorption coefficient of CuInSe2, which is of the order of 105 cm−1 for photons with energies slightly above 1 eV. Models of the operation of CuInSe2/CdS heterojunctions have begun to explain the processes limiting the device performance. The success of the models is based, in part, on the large amount of data which has accumulated on CuInSe2 in spite of the relatively short time it has been extensively studied.