Structural and electronic properties of CdTe_1-xSe_x films and their application in solar cells

Abstract

The performance improvement of conventional CdTe solar cells is mainly limited by doping concentration and minority carrier life time. Alloying CdTe with an isovalent element changes its properties, for example its band gap and behaviour of dopants, which has a significant impact on its performance as a solar cell absorber. In this work, the structural, optical, and electronic properties of CdTe1-xSex films are examined for different Se concentrations. The band gap of this compound changes with composition with a minimum of 1.40 eV for x = 0.3. We show that with increasing x, the lattice constant of CdTe1-xSex decreases, which can influence the solubility of dopants. We find that alloying CdTe with Se changes the effect of Cu doping on the p-type conductivity in CdTe1-xSex, reducing the achievable charge carrier concentration with increasing x. Using a front surface CdTe1-xSex layer, compositional, structural and electronic grading is introduced to solar cells. The efficiency is increased, mostly due to an increase in the short-circuit current density caused by a combination of lower band gap and a better interface between the absorber and window layer, despite a loss in the open-circuit voltage caused by the lower band gap and reduced charge carrier concentration.

Interface Engineering for Both Cathode and Anode Enables Low‐Cost Highly Efficient Solution‐Processed CdTe Nanocrystal Solar Cells

“…For CdSe and CdTe NC active layers, there are no obvious boundaries in the entire two different thin films. The measured lattice parameter for the CdSe x Te 1− x grain is d = 3.89 Å, which is consistent with the value in previous literatures . The whole CdTe and CdSe active layers combine into a homogeneous CdSe x Te 1− x alloy film, which is very important to improve the lifetime of photogenerated carriers and device performance.…”

Kinetic Simulations of Cu Doping in Chlorinated CdSeTe PV Absorbers

“…This result is in agreement with the doping principle formulated by Zunger that predicts worse p ‐dopability for materials with VBM further from vacuum level, which is the case for CdSeTe alloys in comparison with pure CdTe. Our results also agree with the experimentally observed decrease of free carrier concentration with increase of Se content in CdSeTe alloy . Since the poor activation of Cu doping in high‐Se regions may weaken the collection efficiency, the optimal design of Se profile in graded CdSeTe absorbers is required to provide a tradeoff between the generation and collection of the free carriers.…”

CdTe‐Based Solar Cells with Variations in Mg Concentration in the MgZnO Emitter

“…[5][6][7][8] Meanwhile, incorporation of Se to form a ternary alloy of CdSe x Te 1Àx adjacent the emitter has further improved the current collection at longer wavelengths. [9][10][11][12][13][14][15] The Se alloy layer has been shown to be effective both because of its narrower bandgap (%1.4 eV), which allows additional photon collection, and because of the increased passivation when deployed as an absorber layer adjacent to the MZO emitter. [13,16,17] The full structure of the cells used in this work is shown in Figure 1a.…”