Below the Urbach Edge: Solar Cell Loss Analysis Based on Full External Quantum Efficiency Spectra

Abstract

We suggest a new solar cell loss analysis using the external quantum efficiency (EQE) measured with sufficiently high sensitivity to also account for defects. Unlike common radiative-limit methods, where the impact of deep defects is ignored by exponential extrapolation of the Urbach absorption edge, our loss analysis considers the full EQE including states below the Urbach edge and uses corrections for band-filling and light-trapping. We validate this new metric on a whole range of photovoltaic materials and verify its accuracy by electrical simulations. Any deviations between the new metric and experimental open-circuit voltage are due to the presence of spatially localized defects and are explained as violations of the assumption of flat quasi-Fermi levels through the device.

Hyperspectral Photoluminescence Imaging for Spatially Resolved Determination of Electrical Parameters of Laser‐Patterned Perovskite Solar Cells

“…[16,42] In general, the Urbach energy is related to the density of state distribution near the band edges and is therefore commonly used as an indicator of the electronic quality of thin films used as absorbers in solar cells. [40,[42][43][44] Thus, determining the Urbach energy is a useful tool to identify and address material-related issues that may affect device performance. A lower E u typically indicates a lower concentration of defects or trap states within the material, which corresponds to a higher material quality that is crucial for efficient solar cell performance.…”

“…For disordered materials such as organic or semi-organic solids, which include PSCs, the applicability and significance of the Urbach energy is still under discussion. [40,44] Nevertheless, it has been shown also for PSC that the empirical correlation between low Urbach energies and the open-circuit voltage deficit holds. [41][42][43] Thus, E u can be directly interpreted as measure of the local solar cell performance, since it provides information about material quality, defect states, non-radiative recombination, and the efficiency of light absorption.…”

An Experimental and Simulation Study of Cu6BiAgI10 Photovoltaics with Various Organic and Inorganic Hole Transport Layers for the Improved Photovoltaic Performance of Solar Cells

“…A study of quantum efficiency (QE) is essential for the assessment and improvement of photovoltaic cells, as it gives valuable insights into the efficiency with which incident photons are converted into electricity. It allows the identification of areas for improvement and a better understanding of the mechanisms behind the loss of energy in cells. , As shown in Figure b, the corresponding QE was investigated as a function of wavelength (300–800 nm). The value of QE started increasing at 300 nm, and then it increased by almost 80% in a nanometer range of 350.…”