Ultrahigh-Frequency Heterodyne Lock-In Carrierography for Large-Scale Quantitative Multi-Parameter Imaging of Colloidal Quantum Dot Solar Cells

Abstract

Ultrahigh-frequency heterodyne lock-in carrierography (UHF-HeLIC) is a new near-IR dynamic photoluminescence (PL) camera-based large-area imaging technique. It is specifically developed for investigating dynamic optoelectronic events that occur at very fast diffusion-wave rates (> = 10 kHz), above which conventional camera imaging cannot be achieved. The nonlinear combination of two-frequency-modulated photogenerated carrier density waves (CDWs) with a 10 Hz beat frequency was used to generate HeLIC images in the UHF range (up to 270 kHz) above the effective CDW recombination rate. Using sequences of these high-frequency images and UHF-HeLIC theory, carrier lifetime, diffusivity, and diffusion and drift length images were reconstructed from colloidal quantum dot solar cells and used for studying the influence of surface and interface trap states on photocarrier transport processes. The new non-destructive UHF-HeLIC imaging methodology shows excellent potential for industrial in-line photovoltaic device characterization, fundamental optoelectronic physical process studies, and various other photoelectronic applications.