wei Li

Effects of growth process on the optical and electrical properties in Al-doped ZnO thin films

Aluminum doped zinc oxide (AZO) has attained prominence as being a very good transparent conducting oxide for optoelectronics and photovoltaic applications. In this work, we report on the synthesis and characterization of AZO films with c-axis preferred orientation using magnetron radio frequency (RF) sputtering. It was found that the degree of the c-axis preferred orientation can be controlled by varying the growth conditions, such as working pressure, RF power, and substrate temperatures. The preferred orientation increased as the working pressure decreased, while it increased as the RF power and substrate temperature increased. Electrical and optical measurements have revealed that the growth conditions and c-axis preferred orientation have strong influence on the physical properties of the synthesized AZO thin films. The thin films with increased c-axis preferred orientation exhibited enhanced carrier mobility.

A low temperature processed fused-ring electron transport material for efficient planar perovskite solar cells

A fused-ring electron acceptor based on indacenodithiophene (IDIC) was used to replace TiO2 and work as an electron transport layer in planar n–i–p perovskite solar cells. IDIC improves perovskite crystallinity and film quality due to its hydrophobicity and incompatible wetting surface. IDIC facilitates electron extraction and transport due to its high mobility and suitable energy levels matched with the perovskite. IDIC reduces charge recombination in the devices due to trap passivation at the perovskite surface. The IDIC-based devices exhibit a champion power conversion efficiency of 19.1%, which is higher than that of TiO2-based devices (17.4%). Moreover, the device stability is significantly improved by IDIC.

Stability, transparency, and conductivity of MgxZn1−xO and CdxZn1−xO: Designing optimum transparency conductive oxides

The stability, transparency, and conductivity of ZnO are suggested to be tailored by alloying with MgO or CdO to meet wide applications. Our Monte Carlo simulation based on first-principle cluster expansion methods partially explain the solubility and stability data scattered in extensive experiments and further reveal that CdxZn1−xO has much higher solubility than prevalent MgxZn1−xO in a large range of experimentally achievable temperature (400 K–1200 K). Furthermore, first-principles calculations based on hybrid functional methods show that CdxZn1−xO has better n-type doping properties than MgxZn1−xO. The optical gap of CdxZn1−xO could be ∼1.5 eV higher than its fundamental gap due to large Moss-Burstein shift. We thus predict that CdxZn1−xO has great potential to be a better transparent conducting oxide than MgxZn1−xO.

Pyramid size control and its effects on the performance of silicon heterojunction solar cells

This paper explores the formation process of surface pyramid morphologies and etching characteristics during the texturing process of silicon heterojunction (SHJ) solar cells. Our research discovered that pyramid size followed a linear correlation with etch amount at the transition point of planes {100} to {111} as the etch rate reached the transition point. Several techniques were developed to control pyramid size by monitoring and adjusting the etching amount at the transition point. Using this approach, the average pyramid size was successfully controlled from 0.5 μm to 12 μm. We concluded that for pyramids smaller than 1 μm or greater than 12 μm, the light reflectance, minority carrier lifetime (MCLT), and performance of SHJ solar cells were adversely affected. In conclusion, a desirable range of pyramid sizes was empirically determined by our investigation.

Development of ito/layered a-P Si:H film stack for silicon heterojunction solar cells

This work focuses on the development of integrated front side film stack containing a-p Si:H film as the emitter and ITO film as the carrier collection layer in n-type silicon heterojunction (SHJ) solar cells. Doping concentration and thickness of a-p Si:H films, and O2/Ar flow ratio of DC sputtered ITO films were varied to obtain optimal single layer properties. A combined ITO/double a-p Si:H stack was then developed and optimized to improve fill factor (FF) of SHJ solar cells. As a result, FF higher than 78% with conversion efficiency of 21.6% have been achieved in this work.