D-A-D Structured Polymer Interlayer for Higher Open-Circuit Voltage and Stability in MAPbI3 Perovskite Solar Cells

Mukherjee, R and Srivastava, P and Singh, P and Bhardwaj, S and Saha, A and Viswanathan, VN and Ramamurthy, PC and Avasthi, S (2022) D-A-D Structured Polymer Interlayer for Higher Open-Circuit Voltage and Stability in MAPbI3 Perovskite Solar Cells. In: Journal of Electronic Materials .

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Abstract

The open-circuit voltage (Voc) in a thin-film n-i-p-type perovskite solar cell (PSC) depends on the quasi-Fermi-level splitting (QFLS) in the perovskite layer. Recent photo/electroluminescence measurements show that the Voc in practical devices is lower than the QFLS in the bare perovskite film, suggesting that the device performance is limited by the interfaces. The losses at the perovskite/transport layer (TL) interface can be caused by (a) the suboptimal band alignment between perovskite and TL, or (b) the interface defects. Previously, we reported a polymer interlayer, poly-4-(5-(9,9-dihexyl-7-methyl-9H-fluoren-2-yl)thiophen-2-yl)-5,6-difluoro-7-(5-methylthiophen-2-yl)benzoc1,2,5thiadiazole (PF-DTDFBT) having efficient band matching with valence band maxima (VBM) of perovskite (MAPbI3), which enhanced the Voc of the n-i-p structured PSC. In this report, we established the reason for the higher Voc. Firstly, the x-ray photoelectron spectroscopy and carrier lifetime measurements show that the polymer does not passivate the surface of the perovskite, and hence interface defects do not limit the Voc. On the other hand, comparison of the highest occupied molecular orbital (HOMO) of the polymer with that of Spiro-OMeTAD, shows that the alignment with the VBM of MAPbI3 is better for polymer than for Spiro-OMeTAD. From these two observations, it is inferred that the enhancement in Voc is due to the efficient HOMO/VBM alignment of the polymer interlayer and the perovskite (MAPbI3). As perovskite film quality and defect density are heavily dependent on the fabrication process, the device fabrication and stability measurements were repeated with the widely accepted planar antisolvent-treated perovskite films (as compared with the methylamine vapor-treated films used previously). The planar, antisolvent recipe-based devices showed enhanced performance for both Spiro-OMeTAD (reference) and polymer-interlayer-based devices. The power conversion efficiency (PCE) of the polymer interlayer device was 16.51% with Voc of 1.11 V compared with PCE of 14.72% and Voc of 1.04 V for the reference Spiro-OMeTAD-based devices. The polymer being hydrophobic, enhanced the stability of the interlayer devices, whose PCE drops by only 22% after 240 h of exposure to 72 ± 3% relative humidity as compared with a 60% drop in efficiency of the reference Spiro-OMeTAD devices kept in the same ambient conditions and time frame.

Item Type:	Journal Article
Publication:	Journal of Electronic Materials
Publisher:	Springer
Additional Information:	The copyright for this article belongs to Springer.
Keywords:	Carrier lifetime; Molecular orbitals; Perovskite; Perovskite solar cells; Stability; Thin film circuits; Thin films; Timing circuits; X ray photoelectron spectroscopy, Bi-layer; Bilayer hole transport layer; Halide perovskites; Hole transport layers; Open-circuit voltages; Perovskite films; Perovskite layers; Power conversion efficiencies; Quasi-Fermi level splitting; Valence-band maximums, Open circuit voltage
Department/Centre:	Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy) Division of Interdisciplinary Sciences > Centre for Nano Science and Engineering
Date Deposited:	08 Oct 2022 04:19
Last Modified:	08 Oct 2022 04:19
URI:	https://eprints.iisc.ac.in/id/eprint/77302

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