Investigating CdTe solar cell performance through glass/TCO selection and CdSe-based window layer engineering

Abstract

As energy demand continues to rise, it is imperative that energy production becomes more efficient. Thin-film cadmium telluride (CdTe) photovoltaic technology is advantageous compared to many other energy sources due to its low material cost, ease of manufacturing, and high throughput. However, several challenges remain before CdTe photovoltaics reach full commercial maturity. This research is divided into two specific aims. The first is to investigate the optical and electronic properties of commercially available glass/TCO superstrates to identify those most suitable for high-performance CdTe devices. The second is to explore the mechanics of device structures that do not rely on magnesium-doped zinc oxide (MZO) as the n-type buffer layer. To address the first aim, three glass/TCO superstrates (TEC10, TEC12D, and a proprietary glass/TCO stack) were compared using optical transmission and reflection measurements, along with Hall effect characterization. Devices fabricated using the proprietary glass/TCO exhibited superior performance, with higher current density attributed to increased optical transmission, especially above 700 nm. To address the second aim, a series of experiments were conducted on alternative device structures that did not utilize CdSe. These experiments explored various CdSe thicknesses and CdCl2 treatment conditions to evaluate their impact on CdSe based devices. While thicker CdSe improved VOC, it reduced JSC due to parasitic absorption. To overcome this tradeoff, a CdSexTe1-x (CST) ternary alloy was introduced to help control Se diffusion and improve band alignment. Devices incorporating CST showed improved performance across both voltage and current, highlighting its effectiveness in balancing interface properties and enabling high-efficiency, CdSe based device architectures. These results underscore the importance of front contact optimization and buffer layer engineering in advancing CdTe photovoltaic efficiency.