(775d) Characterizing Defects in Photovoltaic Semiconductors with Optical Spectroscopy
In this work, high-resolution voltage-, temperature-, and intensity-dependent TRPL data for chalcopyrite, kesterite, and perovskite devices and absorbers are analyzed to determine the origin of the PL decay time. Additionally, a supercontinuum excitation source is used to investigate the excitation energy-dependence of the PL decay time. Such measurements allow us to distinguish the various PL decay rate limiting mechanisms for these materials. We find chalcopyrite absorbers â including CuInSe2 (CISe) and Cu(In,Ga)Se2 (CIGSe) â from a variety of processing conditions and compositional profiles follow the expected behavior for ShockleyâReadâHall (SRH) recombination limited decay times. The impact of carrier diffusion and surface recombination are demonstrated. In contrast, TRPL analysis of kesterite devices â including Cu2ZnSnSe4 (CZTSe) and Cu2ZnSn(S,Se)4 (CZTSSe) from various processing conditions â suggests that PL decay times are not directly related to the recombination lifetime for CZTSSe. A model for minority carrier trapping in shallow donor states is proposed to explain the measured TRPL behavior for kesterites. These results illustrate the importance of measurement conditions and careful analysis when interpreting TRPL data, and further elucidate the defect related device limitations in chalcogenide solar cells.