Cadmium telluride (CdTe) photovoltaics is a promising and scalable technology, commanding over 90% of the thin film photovoltaics market. An appropriate window layer is crucial for high-efficiency CdTe solar cells. This study aimed to investigate a representative MgZnO (MZO) window layer and enhance device performance. We studied the properties of MZO films with different substrate temperatures and their application in CdSeTe/CdTe solar cells. Despite the high transmittance and wide band gap of MZO film, the device performance of MZO sputtered at room temperature is limited by excessive conduction band offset. Tailoring the substrate temperature for MZO sputtering helps optimize the band alignment of the MZO/CdSeTe interface, contributing to an improvement in the efficiency of CdTe solar cells.

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.

The band alignment between magnesium-doped zinc oxide (MZO) and cadmium telluride (CdTe) is critical for enhancing the efficiency of CdTe solar cells. In order 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 the MZO films, with the target bias ranging from 79 V to 121 V. The compositional, structural, chemical, and electronic properties of the MZO films were investigated. The optical transmission and x-ray photoelectron spectroscopy results show 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 99 V, 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, decrease the photo-generated current, negatively impacting device performance. The results emphasize the significance of DC bias in the RF sputtering process of MZO films with regard to the functionality of CdTe solar cells.