Perfluorinated Self-Assembled Monolayers Enhance the Stability and Efficiency of Inverted Perovskite Solar Cells

Abstract

Perovskite solar cells are amongst the most exciting photovoltaic systems as they combine low recombination losses, ease of fabrication and high spectral tunability. The Achilles heel of this technology is the device stability due to the ionic nature of the perovskite crystal, rendering it highly hygroscopic, and the extensive diffusion of ions especially at elevated temperatures. Herein, we demonstrate the application of a simple solution-processed perfluorinated self-assembled monolayer (p-SAM) that not only passivates the perovskite surface but also drastically improves the stability of the perovskite absorber and in turn the solar cell under elevated temperature or humid conditions. p-i-ntype perovskite devices employing these SAMs exhibited power conversion efficiencies surpassing 21%. Notably, the best performing devices are stable under standardized maximum-power point (MPP) operation at 85°C in inert atmosphere (ISOS-L-2) for more than 250 h, and exhibit superior humidity resilience, maintaining ~95% device performance even if stored in humid air in the ambient over months (~3000h, ISOS-D-1). Our work, therefore, demonstrates a novel strategy towards efficient and stable perovskite solar cells with easily deposited functional interlayers. Supporting Information.Experimental Methods, Supplementary Notes and Calculations, Details on Simulation, XRD, UV-Vis, XPS, FTIR, KP data, PL vs time, SPV measurements as well as additional experimental methods.

Tuning halide perovskite energy levels

“…There is evidence that the latter could also be related to the presence of an electric field generated by the dipoles, which can push away the electrons from the interface 55 . It is also worth highlighting the consistency of this behaviour with the results from a previous work employing IPFC10 at the interface between perovskite and C60 in n-i-p PSCs 35 ,…”

“…This molecule is already known in the literature for being able to form self-assembled monolayers and enhance the efficiency and stability of perovskite solar cells. 33,35 In this molecule, the iodine on the head remains slightly positive thanks to the electrons withdrawing effect of the fluorinated chain, which allows the molecule to behave like a Lewis acid and form halogen bond [36][37][38][39] with the halogen ions on the perovskite surface. To evaluate the WF shift we performed KP [40][41][42][43] measurements in different conditions ( To have a better idea of the real magnitude of the WF shift induced by the functionalization, we also performed KPFM [43][44][45] measurements on non-air exposed samples.…”

Applications of Self‐Assembled Monolayers for Perovskite Solar Cells Interface Engineering to Address Efficiency and Stability

“…Reproduced with permission. [154] Copyright 2020, American Chemical Society. www.advancedsciencenews.com in perovskite and making the surface hydrophobic, which can increase the moisture stability.…”

“…Various techniques have been adopted in the last few years to passivate traps, some of them including SAMs as successful passivates to alleviate crystal defects in both metal oxides and perovskites. [80,100,154] For example, the carboxylate anchoring group incorporated into fullerene-based SAMs forms chemical bonding with the hydroxyl group on metal oxides. [163] X-ray photoelectron spectroscopy (XPS) investigations have revealed the presence of unsaturated Pb 0 on the perovskite surface due to the oxidation of I − to I 2 .…”

“…[ 154 ] The p‐SAM modified PSCs exhibited 21% efficiency, retained ≈95% of its original efficiency for ≈3000 h in ambient conditions as shown in Figure 9c, and was stable at maximum power point tracking at 85 °C for more than 250 h. The SAM modification reduced the moisture ingress, which effectively increased the device stability. [ 154 ] For the first time, Magomedov and co‐workers [ 155 ] used SAMs as an HTL in p‐i‐n PSCs achieving a high fill factor (FF) of 80% and a high PCE of 17.8%. Al‐Ashouri and co‐workers have utilized SAMs consisting of carbazole bodies molecules having anchoring groups of phosphonic acid in PSCs.…”