Recently, we have suggested a new solar cell loss analysis by using the absorptance or simple external quantum efficiency (EQE) measured with sufficiently high sensitivity to also account for defects [1]. 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 this newly established 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. 

Newly, the thermodynamic reciprocity between photoluminescence and absorptance will be discussed and the method of experimental determination of light trapping path enhancement factor will be introduced. Method is based on comparison of absorptance calculated based on thermodynamic equations from photoluminescence and absorptance measured by photocurrent technique. Interestingly, if the absorptance curve features less steep absorption edge, so that the Urbach energy is higher than kT, then band filling correction has to be used for calculations. Results are validated experimentally on the pure iodide and mixed halide perovskite layers deposited on substrates with different roughness, see Figure 1.

The work was supported by the Czech Science Foundation grant no 23-06543S

 

[1] Holovský, J.; Ridzoňová, K.; Peter Amalathas, A.; Conrad, B.; Sharma, R. K.; Chin, X. Y.; Bastola, E.; Bhandari, K.; Ellingson, R. J.; De Wolf, S. Below the Urbach Edge: Solar Cell Loss Analysis Based on Full External Quantum Efficiency Spectra. ACS Energy Lett. 2023, 8 (7), 3221–3227. https://doi.org/10.1021/acsenergylett.3c00951.