High efficiency CdTe solar cells by low temperature deposition with MgZnO HRT layer

CdTe solar cells have shown high efficiency and the technology is scalable. As a result thin film CdTe modules are competitive with crystalline silicon modules. Thin film CdTe devices with efficiency above 22% have been reported using high substrate temperatures during the deposition process. It is known that high substrate temperatures result in large grain size with a reduced number of grain boundaries and this is believed to contribute to the high efficiency. However, use of high temperature requires robust substrates and excludes the use of most flexible substrate materials. It also involves higher energy consumption and more complicated machinery. In this work we present a process for high efficiency solar cells with an improved front contact, by introducing magnesium-doped zinc oxide high resistance transparent layer. By optimizing the fabrication process we have achieved a conversion efficiency exceeding 16%, which is one of the highest reported for substrate temperatures below 500°C

Water (H₂O and D₂O) Dispersible NIR-to-NIR Upconverting Yb³⁺/Tm³⁺ Doped MF₂ (M = Ca, Sr) Colloids: Influence of the Host Crystal

Tm³⁺/Yb³⁺ doped CaF₂, SrF₂, and cubic phase NaYF₄ nanoparticles dispersed as colloids in water (H₂O and D₂O) or saline solutions have been directly prepared by a one-step hydrothermal technique, using citrate anions as capping agents, without the need for any postsynthesis reaction. The size monodispersed nanoparticles are directly dispersed in water. Comparison of the upconversion emissions at 800 nm (Tm³⁺ ions) among the CaF₂, SrF₂, and NaYF₄ hosts indicates that the SrF₂ host leads to the highest emission intensity, 2 orders of magnitude higher than the NaYF₄ one. Alkali ions (Na⁺ or K⁺) counter cations of the citrate salts used as precursors can enter the fluoride host crystals as charge compensators and strongly influence the spectroscopic properties of the lanthanide ions. The Tm³⁺/Yb³⁺ doped SrF₂ nanoparticles dispersed in a 0.4 g/L concentration solution show detectable upconversion with laser excitation intensities as low as 1 W/cm²