Stress and strain analysis of Cu plated contacts on HJT cells under different annealing conditions

When applying Cu metallization to silicon solar cells, promotion of metal contact adhesion is typically achieved by an annealing process, during which the material's microstructures can be modified, such as lattice parameter, crystallographic orientation and microstrain. Nanoindentation, X-ray diffraction and Raman spectroscopy were performed to quantify the development of stress and strain of Cu plated contacts on silicon heterojunction (HJT) solar cells. Comparison between self-annealing and fast annealing was investigated. It is shown that thermal annealing at 200 °C did not alter Young's modulus, yield strength and grain size of plated Cu. Compared to self-annealing, fast annealing reduced Cu lattice parameter, increased indium tin oxide (ITO) lattice parameter, increased microstrain of both Cu and ITO, and hence increased local stress in Si at the metal contact edges. • Annealing at 200 °C did not change the grain size and yield strength of plated Cu contacts on HJT solar cells. • Fast annealing at 200 °C resulted in a reduced lattice parameter of Cu when compared to self-annealing. • Higher dislocation density was formed in the prevalent Cu (111) plane. • Both Cu and ITO microstrains were increased by fast annealing. • Raman spectroscopy showed ∼2 μm wide local high stress was induced in Si along the plated Cu fingers. • Self-annealed Cu introduced lower medium relative stress of Si than fast annealed Cu.