The UPS results indicated that although the electron affinity of ZnO could be effectively tuned by doping Ga, it remained quite stable for GZO under oxygen rich condition.

The band alignment between Magnesium doped Zinc Oxide (MZO) and Cadmium Telluride (CdTe) is a critical for enhancing the efficiency of CdTe solar cell. To study the effect of Direct Current (DC) bias on the MZO film, various DC biases were applied during the Radio Frequency (RF) sputtering of MZO films, with target bias ranging from 79V to 121V. The compositional, structural, chemical, and electronic properties of the MZO films were investigated. The optical transmission and XPS results showed that the DC bias could modify the position of the Fermi level while having minimal impact on the band gap of the MZO film. The MZO films with different DC biases were employed as the window layer in CdTe solar cells. The device without DC bias exhibited a low efficiency of 7.7%, corresponding to a cliff-like conduction band offset near -0.1 eV. The optimal DC bias for the MZO film was found to be 99V, leading to an improvement in efficiency to 12.9%, with a spike-like conduction band offset near 0.2 eV. Further increases in the conduction band offset, however, decreased the photo-generated current, negatively impacting device performance. The results emphasize the significance of DC bias in the RF sputtering process of MZO films in regards to the functionality of CdTe solar cell.

No abstract

Opto-electrical properties of MgxZn1−xO can be tuned by adjusting the value of x, but phase separation occurs when x is greater than 0.4. Hydrogen acts as a shallow donor in MgxZn1−xO and can play an important role in tuning the opto-electrical properties in a way that avoids phase separation. Mg0.1Zn0.9O (MZO) films were prepared at different hydrogen partial pressures and their structures and properties were studied. XRD results show that the MZO film has a wurtzite structure with a preferential orientation along the c-axis, but the crystallinity declines with increasing hydrogen partial pressure. Stress in the MZO film changes from tensile to compressive as the hydrogen partial pressure increases. Increasing the hydrogen partial pressure improves the conductivity and increases the optical bandgap, but the electronic affinity of MZO decreases, according to ultraviolet photoelectron spectroscopy results. These key parameters were used to simulate a device with a TCO/MZO/CdTe/ZnTe:Cu type structure, in which TCO is the transparent conductive oxide. The highest efficiency of 17.37% was achieved when the electron affinity of the MZO film was 3.71 eV, corresponding to a spark-like band offset of 0.29 eV at the MZO/CdTe interface. These results suggest that the electron affinity of MZO can be tuned to achieve an optimal band alignment in the device.