Xu Shengzhi

Influence of selenium evaporation temperature on the structure of Cu2ZnSnSe4 thin film deposited by a co-evaporation process

Cu2ZnSnSe4 (CZTSe) thin film solar cells have been fabricated using a one-step co-evaporation technique. The structural properties of polycrystalline CZTSe films deposited at different selenium evaporation temperatures (TSe) have been investigated using X-ray diffraction spectra, scanning electron microscopy, and atomic force microscopy. A relationship between TSe and the secondary phases deposited in the initial stage is established to explain the experimental observations. The Se flux is not necessarily increased too much to reduce Sn loss and the consumption of Se during fabrication could also be reduced. The best solar cell, with an efficiency of 2.32%, was obtained at a medium TSe of 230 °C (active area 0.34 cm2).

Improvement of the Open Circuit Voltage of CZTSe Thin-Film Solar Cells by Surface Sulfurization Using SnS*

The objective of this study is to find an effective method to improve Voc without Jsc loss for Cu2ZnSnSe4 (CZTSe) thin film solar cells, which have been fabricated by the one step co-evaporation technique. Surface sulfurization of CZTSe thin films is carried out by using one technique that does not utilize toxic H2S gas; a sequential evaporation of SnS after CZTSe deposition and the annealing of CZTSe thin films in selenium vapor. A Cu2ZnSn(S,Se)4 (CZTSSe) thin layer is grown on the surface of the CZTSe thin film after the annealing. The conversion efficiency of the completed device is improved due to the enhancement of Voc, which could be attributed to the formation of a hole-recombination barrier at the surface or the passivation of the surface and grain boundary by S incorporation.

Impact of Cu-rich growth on the Cu2ZnSnSe4 surface morphology and related solar cells behavior*

In order to study the influence of Cu-rich growth on the performance of the Cu2ZnSnSe4 (CZTSe) thin film solar cells, a multi-stage co-evaporation process is applied. The CZTSe films are grown at a lower substrate temperature to reduce the existence time of Cux Sey at the first period caused by the volatility of SnSex. This study examines the surface morphology and device performance in Cu-rich growth and close-to-stoichiometric growth. Although the grain size of Cu-rich growth film increases a little, the difference was not dramatic as the results of CIGS reported previously. A model based on the grain boundary migration theory is proposed to explain the experimental results. The mechanisms of Cu-rich growth between CZTSe and CIGS might be different.

Influence of Different Pyramidal Structural Morphologies of Crystalline Silicon Wafers for Surface Passivation and Heterojunction Solar Cells

Silicon heterojunction (SHJ) solar cells consisting of a hydrogenated amorphous silicon (a-Si:H) film deposited on a crystalline silicon wafer have attracted considerable attention from the photovoltaic industry, because of their high efficiencies, high stabilities, low cost, and low-temperature fabrication. Texturing of silicon surfaces is an effective method for improving the efficiency of silicon solar cells. In this work, textured silicon substrates consisting of three different pyramidal structures were obtained using tetramethylammonium hydroxide (TMAH) solution, and used to fabricate SHJ solar cells. We investigated the influence of different pyramidal structural morphologies on the optical properties and electronic performances, to identify the optimum structure for SHJ solar cells. We obtained a standard silicon substrate with four-sided pyramidal structures using 2% (w) TMAH and 10% (w) isopropyl alcohol (IPA). In comparison with other pyramidal structures, the standard four-sided pyramidal-structured silicon substrate had the lowest reflectance, leading to an increased short-circuit

Reduction of the phosphorus contamination for plasma deposition of p-i-n microcrystalline silicon solar cells in a single chamber

This paper investigates several pretreatment techniques used to reduce the phosphorus contamination between solar cells. They include hydrogen plasma pretreatment, deposition of a p-type doped layer, i-a-Si:H or μc-Si:H covering layer between solar cells. Their effectiveness for the pretreatment is evaluated by means of phosphorus concentration in films, the dark conductivity of p-layer properties and cell performance.