AVS 62nd International Symposium & Exhibition
    Energy Frontiers Focus Topic Monday Sessions
       Session EN+AS+EM+NS+SE+SS+TF-MoM

Paper EN+AS+EM+NS+SE+SS+TF-MoM10
The Role of ZnTe Buffer Layers on the Performance and Stability of CdTe Solar Cells

Monday, October 19, 2015, 11:20 am, Room 211B

Session: Solar Cells I
Presenter: Jiaojiao Li, Colorado School of Mines
Authors: J. Li, Colorado School of Mines
A. Abbas, Loughborough University, UK
D.M. Meysing, Colorado School of Mines
J.D. Beach, Colorado School of Mines
D.R. Diercks, Colorado School of Mines
M.O. Reese, National Renewable Energy Laboratory
T.M. Barnes, National Renewable Energy Laboratory
C.A. Wolden, Colorado School of Mines
J.M. Walls, Loughborough University, UK
Correspondent: Click to Email
The use of ZnTe buffer layers at the back contact of CdTe solar cells has been credited with contributing to recent improvements in both record cell efficiency and module stability. To better understand the underlying reasons high resolution transmission microscopy (HR-TEM) and atom probe tomography (APT) were used to study the evolution of the back contact region before and after rapid thermal activation of this layer. During activation the 150 nm ZnTe layer, initially nanocrystalline and homogenous, transforms into a bilayer structure consisting of an amorphous region in contact with CdTe characterized by significant Cd-Zn interdiffusion, and a crystalline layer that shows evidence of grain growth and twin formation. This graded layer may passivate interface defects and account fo the improved open circuit voltage and fill factor that accompanies the RTP activation step. Copper, co-evaporated uniformly within ZnTe, is found to segregate dramatically after rapid thermal activation, either collecting near the ZnTe|Au interface or forming CuxTe clusters in CdTe at defects or grain boundaries near the interface. Further examination of the CuxTe clusters revealed that they are encased in a thin layer of Zn, and it is postulated that this structure may limit the extent of diffusion into CdTe and play an important role in device stability.