Improving the minority carrier lifetime of iodine-doped n-type CdTe via surface passivation

Surface recombination critically limits the performance of CdTe photovoltaics, yet most passivation studies focus on p -type thin films. Here, we systematically investigate bromine (Br), iodine (I), cadmium chloride (CdCl 2 ), and selenium (Se) treatments on iodine-doped n -type CdTe (CdTe:I) single crystals using time-resolved photoluminescence (TRPL), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). Br passivation most effectively suppresses surface recombination, yielding the highest photoluminescence (PL) intensity and longest near-surface lifetime, while CdCl 2 produces the longest bulk lifetime. XPS and Raman reveal that Br replaces Te-rich surface states with stable Te–Br/Cd–Br terminations, thereby passivating dangling bonds despite partial TeO x formation; I forms weak Te–I/Cd–I bonds that decompose easily and accelerate oxidation, creating sub-oxide traps; CdCl 2 reconstructs the surface into a Cd-rich, stoichiometric Cd–Te phase with minimal TeO x ; and Se forms CdSe at the interface without effective passivation. These results clarify the chemical mechanisms underlying each treatment and establish clear design principles for achieving stable and effective surface and bulk passivation in next-generation n -type CdTe photovoltaic and optoelectronic devices.