Subsurface Photoluminescence Lifetime Imaging of Photovoltaic Materials using Multiphoton Tomography

摘要

Multiphoton tomography based on tunable femtosecond near infrared 80 MHz laser radiation has been used to map twophoton-excited time-resolved photoluminescence with picosecond temporal resolution from in-bulk thin photovoltaiclayers. The time-resolved photoluminescence reflects carrier lifetimes and is therefore an important measure for theefficiency of a solar cell. Conventional one-photon solar cell characterization methods are dominated by surface effectsand cannot provide information on subsurface carrier dynamics. In contrast, by using two-photon excitation, subsurfacecarrier dynamics can be monitored in 3D, providing morphological and spatial information on local defects andcrystalline grain boundaries We present results on time-resolved photoluminescence and second harmonic generationimaging in forward and backward directions of CdTe/CdS films by time-resolved single photon counting and false-colorphotoluminescence mapping. High-resolution two-photon optical sectioning was carried out with a modified multiphotonFLIM tomograph MPTflex employing near-infrared sensitive photodetectors.