What defines the perovskite solar cell efficiency and stability: fullerene-based ETL structure or film morphology?

SUSTAINABLE ENERGY & FUELS. 2023. Vol. 7. No. 16. P. 3893–3901.

Elnaggar M., Mumyatov A., Emelianov N., Gutsev L., Ozerova V., Fedyanin I., Nelyubina Y., Troyanov S., Ramachandran B., Troshin P.

In this contribution, we report the synthesis and structural characterization of a series of fullerene derivatives and their further systematic investigation as promising ETL (electron transport layer) materials in p–i–n perovskite solar cells (PSCs). The devices fabricated using a set of fullerene derivatives F1–F6 demonstrated high power conversion efficiencies (PCEs), up to 19.0%, compared to the 17.3% obtained with reference cells assembled using the benchmark ETL material, [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM). The improved photovoltaic performance of PSCs incorporating the fullerene derivatives originated from a decreased trap density at the perovskite/ETL interface and full coverage of the perovskite absorber layer, which was revealed by the photoluminescence (PL) spectra and infrared scattering scanning near field optical microscopy (IR s-SNOM). Also, we enhanced our experimental results with theoretical DFT and DFT-MD calculations which gave further insight on the dependence between the structure and electron mobility in these films. Significantly improved operational stability was achieved for non-encapsulated devices using fluorine-loaded fullerene derivative F5 as the ETL, which retained >60% of the initial efficiency after ∼1300 h of continuous illumination (1 sun), whereas the reference cells with PC61BM as the ETL degraded to ∼40% within 200 h under the same aging conditions. Therefore, the obtained results demonstrated that the molecular structure of the fullerene derivatives affects the performance of PSCs, whereas the film morphology plays a crucial role in defining the operational stability of the devices.

Keywords: solar cells