Non-contacting Optical Probing of Photovoltaic Device Performance

Non-contacting optical probes based on spectroscopic ellipsometry or reflectance measurements are used to predict photovoltaic (PV) device performance and to diagnose optical and electronic losses. Optical modeling of aluminum back surface field (Al-BSF) silicon, thin film cadmium telluride (CdTe), and hybrid organic inorganic lead halide based perovskite (FA1−xCsxPbI3) solar cell technologies are reviewed. Using the near infrared (IR) to ultraviolet (UV) optical properties of PV device component materials and the device structures as input, external quantum efficiency (EQE) spectra are simulated for Al-BSF, CdTe, and perovskite solar cells for comparison with experimental EQE and short circuit current density (JSC). Optical Hall effect measurements of Al-BSF PV determine majority and minority carrier transport properties in the n+ emitter and p-type wafer silicon; from this information open circuit voltage (VOC), fill factor (FF), JSC, and power conversion efficiency (PCE) are calculated and agree well with direct current-voltage (J-V) electrical measurement. An IR-extended optical model for Al-BSF silicon PV includes coherent multiple reflections, ray tracing optics, and diffuse scattering and is applicable as a baseline for developing optical and thermal management strategies. Analysis of EQE for CdTe based solar cells with selenium alloying (CdSe1−yTey) enables determination of absorber composition after full device processing. EQE modeling for perovskite solar cells includes the ability to account for sub gap absorption measured in films but not present in the solar cell absorber and incomplete photogenerated carrier collection in the PV device.