Selective Isolation of Surface Grain Boundaries by Oxide Dielectrics Improves Cd(Se,Te) Device Performance
B Edward Sartor1, Ryan Muzzio1, Chun-Sheng Jiang1
1National Renewable Energy Lab, Golden, Colorado 80401, United States.
ACS Applied Materials & Interfaces
|January 24, 2025
Summary
Solution-processed barrier layers prevent damage to Cadmium Telluride (CdTe) solar cells by isolating grain boundaries during metallization. This isolation is key to improving device performance, with excessive coverage increasing series resistance.
Area of Science:
- Materials Science
- Renewable Energy
- Semiconductor Physics
Background:
- Cadmium Telluride (CdTe) photovoltaics are a leading thin-film solar technology, but efficiency gains are limited by hole contact challenges.
- Solution-processed oxide layers like Aluminum Gallium Oxide (AlGaO) improve open-circuit voltage (VOC) and fill factor (FF) in CdTe devices, though their precise mechanism remains debated.
Purpose of the Study:
- To investigate the role of preferential deposition at grain boundaries by solution-processed layers in improving CdTe solar cell performance.
- To elucidate the mechanism by which these barrier layers enhance device properties and identify optimal application strategies.
Main Methods:
- Investigated the effect of varying Aluminum Gallium Oxide (AlGaO) barrier layer coverage on CdTe surfaces using scanning Auger microscopy.
- Quantified changes in open-circuit voltage (VOC) and fill factor (FF) with respect to barrier layer coverage.
- Examined the impact of grain boundary isolation during metallization on device performance.
Main Results:
- Preferential deposition of barrier layers at grain boundaries effectively isolates them during metallization, preventing absorber damage.
- Optimal barrier layer coverage prevents metallization-induced damage and improves VOC and FF, while excessive coverage increases series resistance.
- The grain boundary isolation effect is material-agnostic, demonstrated with Silicon Dioxide (SiO2) and observed with Molybdenum (Mo) and Zinc Telluride (ZnTe) contacts.
Conclusions:
- Grain boundary isolation during metallization is a critical, previously underappreciated mechanism for improving CdTe solar cell performance.
- Barrier layers protect the CdTe absorber from metallization-induced degradation, with careful control of coverage optimizing efficiency.
- This understanding enables improved contact design strategies for enhanced CdTe photovoltaic devices.
