Revealing the Importance of Front Interface Quality in Highly Doped CdSe_xTe_1–x Solar Cells

Abstract

As carrier concentration improves in CdTe-based solar cells, modeling shows that the front interface becomes a bottleneck for performance. Optimization of the front interface has proven difficult, however, because it both is buried and evolves substantially during standard superstrate device processing. Here, we address both issues by cleaving state-ofthe-art superstrate CdSe x Te 1−x device stacks at the emitter/ absorber interface and reconstructing in the substrate configuration using a Mg y Zn 1−y O/ZnO:Al front contact. By comparing devices that were either copper-or arsenic-doped, the influence of front interface quality on low-doped and highly doped absorbers was studied, respectively. A much larger performance drop was observed for reconstructed arsenicdoped devices, which was attributed to insufficient emitter doping, formation of compensating defects at the front interface, and increased sensitivity to both effects due to a collapsed depletion region. This work highlights key challenges unique to highly doped CdSeTe:As devices that must be addressed moving forward.

Thermomechanical Cleave of Polycrystalline CdTe Solar Cells and its Applications: A Review

“…Reproduced with permission. [ 35 ] Copyright 2021, American Chemical Society. c) Image of large‐area flexible delaminated film and d) JV data for reconstructed flexible device.…”

“…In addition, the front contact layers that were removed during delamination (e.g., SnO 2 , MgZnO) can be reconstructed on the cleaved absorber, enabling high-efficiency substrate devices. [34,35] By delaminating with lightweight, flexible materials, CdTe devices with high specific power (power-to-weight ratio) can be also achieved while maintaining low-costs, high-throughput processing, and material quality associated with high-temperature growth.…”

“…b) JV data for as-grown (superstrate) and reconstructed (substrate) Cu-and As-doped devices. Reproduced with permission [35]. Copyright 2021, American Chemical Society.…”

Water-Assisted Lift-Off Process for Flexible CdTe Solar Cells

“…Currently, there are two main approaches to fabricate lightweight and flexible CdTe solar cells, one is to deposit CdTe stacks on flexible substrates such as ultra-thin willow glass , or metal foils or polymer films, and the other is to transfer CdTe stacks to flexible substrates through a lift-off method. CdTe cells fabricated on willow glass and metal foils have achieved PCEs of 16.4%, and 13.6%, respectively, whereas the lift-off process has achieved a PCE of 15.5% . Overall, the performance of flexible CdTe solar cell is still well below its rigid counterparts …”

“…CdTe cells fabricated on willow glass and metal foils have achieved PCEs of 16.4%, 2 and 13.6%, 4 respectively, whereas the lift-off process has achieved a PCE of 15.5%. 6 Overall, the performance of flexible CdTe solar cell is still well below its rigid counterparts. 1 Lift-off is an attractive approach to fabricate flexible CdTe solar cells due to its low-cost fabrication process.…”