Efficient charge transport is demonstrated in TiO2/PbS quantum dot solar cells where the PbS absorber (∼1.1 eV band gap) is deposited by dip coating and ethanedithiol ligand exchange, with power efficiencies above 3% at AM1.5. An increase in power efficiency occurs as the device temperature is lowered to 170 K, with a open-circuit voltage of 0.66 V, short-circuit current density of 28.6 mA/cm2 and fill factor of 42.4%. This remarkable temperature dependence is due to a large increase in charge transport between the PbS quantum dots with decreasing temperature.

Amorphous films of GeTe, Sb2Te3, and Ge2Sb2Te5 were grown to thicknesses of 0.3–3μm using rf sputtering. The optical properties of these films are influenced by the presence of oxygen impurities. The absorption edge in these glasses is sometimes broader than in “standard” chalcogenide glasses, such as GeSe2 or As2Se3. This result implies either that the valance band consists of highly strained bonds or that large densities of defects exist. In some samples, there exists an electron paramagnetic resonance signal in the absence of any optical excitation, which implies that a large defect density (∼1019cm−3) exists within the energy gap. Below the optical gap the refractive index for Ge2Sb2Te5 is approximately 3.5. Electron spin resonance signals associated with the glassy SiO2 interface with the chalcogenide films are also observed.

The thickness dependence of cadmium telluride/cadmium selenide (CdTe/CdSe) heterojunctions is studied in order to maximize the performance of solar cells. The best overall performance of 3.02% efficiency at air mass 1.5 was achieved from a device with 300 nanometers (nm) of sintered CdTe and 100 nm CdSe, using indium tin oxide and evaporated aluminum as the electrodes. In contrast to thin film CdTe solar cells, the power efficiency was strongly dependent on the thickness of the nanoparticle layer, indicating that the device efficiency is limited by charge transport.

A two-dimensional (2D) organic−inorganic hybrid perovskite (OIHP) material with out-of-plane ferroelectricity is the key to the miniaturization of vertical-sandwich-type ferroelectric optoelectronic devices. However, 2D OIHP ferroelectrics with out-of-plane polarization are still scarce, and effective design strategies are lacking. Herein, we report a novel 2D Dion−Jacobson perovskite ferroelectric semiconductor synthesized by a rigid-to-flexible cationic tailoring strategy, achieving an out-of-plane polarization of 1.7 μC/cm 2 and high photoresponse. Integrating out-of-plane ferroelectricity with excellent photoelectric properties affords a promising platform to investigate ferroelectricity-related effects in vertical optoelectronic devices.

No abstract