A numerical approach to optimize the performance of HTL-free carbon electrode-based perovskite solar cells using organic ETLs

Carbon electrode -based perovskite solar cells (c-PSCs) without a hole transport layer (HTL) have obtained a significant interest owing to their cost-effective, stable, and simplified structure. However, their application is limited by low efficiency and the prevalence of high -temperature processed electron transport layer (ETL), e.g. TiO 2 , which also has poor optoelectronic properties, including low conductivity and mobility. In this study, a series of organic materials, namely PCBM ((Park et al., 2023; Park et al., 2023) [6,6] -phenyl -C61 -butyric acid methyl ester, C72H14O2), Alq 3 (Al(C 9 H 6 NO) 3 ), BCP (2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline, C 26 H 20 N 2 ), C 60 , ICBA (indene-C60 bisadduct, C 78 H 16 ) and PEIE (poly (ethylenimine) ethoxylated, (C 37 H 24 O 6 N 2 ) n ) have been numerically analyzed in SCAPS-1D solar simulator to explore alternative potential ETL materials for HTL-free c-PSCs. The presented device has FTO/ETL/ CH 3 NH 3 PbI 3 /carbon structure, and its performance is optimized based on significant design parameters. The highest achieved PCEs for PCBM, Alq 3 , BCP, C 60 , ICBA, and PEIE-based devices are 22.85%, 19.08%, 20.99%, 25.51%, 23.91%, and 22.53%, respectively. These PCEs are obtained for optimum absorber thickness for each case, with an acceptor concentration of 1.0 x 10 17 cm -3 and defect density of 2.5 x 10 13 cm -3 . The C 60 -based cell has been found to outperform with device parameters as V oc of 1.29 V, J sc of 23.76 mA/cm 2 , and FF of 82.67%. As the design lacks stability when only organic materials are employed, each of the presented devices have been analyzed by applying BiI 3 , LiF, and ZnO as protective layers with the performances not compromised. We believe that our obtained results will be of great interest in developing stable and efficient HTL-free c-PSCs.