Quantification of the charge losses in perovskite solar cells via operando photoluminescence spectroscopy
Weidong Xu a, Lucy Hart a, Benjamin Moss a, James Durrant a
a Centre for Processable Electronics, Department of Chemistry, Imperial College London W12 0BZ, U.K.
International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV22)
València, Spain, 2022 May 19th - 25th
Organizers: Pablo Docampo, Eva Unger and Elizabeth Gibson
Poster, Weidong Xu, 234
Publication date: 20th April 2022

The organic-inorganic metal halide perovskite solar cells (PSCs) have reached over 25% efficiency,[1,2] whilst it is still potential to reach 30% due to severe non-radiative losses either/both in the bulk or/and at the perovskite/charge transport layer interface. Therefore understanding the mechanism of these non-radiative recombination processes is a key to further improve the device performance towards Shockley-Queisser (S-Q) limit.

Photoluminescence (PL) spectroscopy is a non-contact, non-destructive widely used technique to probe radiative recombination so as to interpret non-radiative recombination in materials. Recently, it has shown great success in quantifying the charge losses in PSCs by calculating the quasi-fermi-level-splitting (QFLS) of the perovskite layer .[3,4] Most of the examples were conducted on films or devices at the open-circuit condition, which can only estimate the VOC losses. The device performance, however, is determined by the current-voltage (J-V) scan under a range of voltages from 0V to VOC. In order to fully maximize the use of PL and correlated this method to device performance, we have built an operando PL system to obtain both the absolute PL spectrum and the output current of a PSC at each voltage point during J-V scanning. This system allows us to compare a PL-V curve that can be converted to QFLS-V quantifying the charges remaining in the bulk, to a J-V curve showing the charges extracted to the out-circuit in operando.

p-i-n PSCs with different electron transport layers (ETL) varied LUMOs have been studied in this work. The results suggest that strong surface recombination at the perovskite/ETL interface will induce a mismatch between QFLS and qV, resulting in a discrepancy between PL-V and J-V curve in their shape. Moreover, we’ve also observed large QFLS (>1eV) at short-circuit conditions is a general trend among all the devices, showing strong charge accumulation at the short circuit condition. Our results from Driftfusion simulation suggest that this trend is affected by the interfacial energetic alignment, but more due to a field screening in the bulk caused by mobile ions.

This project is funded by Application Targeted and Integrated Photovoltaics (ATIP) project (EP/T028513/1) and SUNRISE project (EP/T032591/1). W.X. gratefully acknowledges the Imperial- China Scholarship Council scholarship.

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