Microscopic Origins of Contact Deterioration During Annealing of Silicon Heterojunction Solar Cell Contacts

Over the last years, dominating charge carrier transport barrier in silicon heterojunction (SHJ) solar cells could be boiled down to contact of indium–tin oxide (ITO) doped amorphous (a-Si) layer. The formation a parasitic at this junction was hypothesized act as source for deterioration after annealing. However, no experimental proof obtained so far. In contribution, we simultaneously investigate resistivity and nanoscopic structure electron SHJ cell annealing temperature range between 140 $^\circ \text{C}$ 240 . For purpose, micro transfer length measurements, time-of-flight secondary ion mass spectrometry, electron–energy loss spectroscopy well energy-dispersive X-ray (scanning) transmission microscope are applied. A minimum around 120 notation="LaTeX">$\text{m}\Omega {\text{cm}^{2}}$ is 160 At higher temperatures, resistivities increase rapidly. This degradation correlates with thickening layer found ITO/a-Si an Si oxidation state within interlayer. Additionally, Ag from metallization diffuses into Si, which may induce deep acceptor trap states. Furthermore, TiO notation="LaTeX">${}_{\text{x}}$ notation="LaTeX">${\text{x}}\sim {1}$ proven ITO AgPdTi metallization, does not impair current transport.