Fluorine Functionalized Graphene Nano Platelets for Highly Stable Inverted Perovskite Solar Cells

Abstract

Edged-selectively fluorine (F) functionalized graphene nanoplatelets (EFGnPs-F) with a p-i-n structure of perovskite solar cells achieved 82% stability relative to initial performance over 30 days of air exposure without encapsulation. The enhanced stability stems from F-substitution on EFGnPs; fluorocarbons such as polytetrafluoroethylene are well-known for their superhydrophobic properties and being impervious to chemical degradation. These hydrophobic moieties tightly protect perovskite layers from air degradation. To directly compare the effect of similar hydrophilic graphene layers, edge-selectively hydrogen functionalized graphene nanoplatelet (EFGnPs-H) treated devices were tested under the same conditions. Like the pristine MAPbI perovskite devices, EFGnPs-H treated devices were completely degraded after 10 days. The hydrophobic properties of EFGnPs-F were characterized by contact angle measurement. The test results showed great water repellency compared to pristine perovskite films or EFGnPs-H coated films. This resulted in highly air-stable p-i-n perovskite solar cells.

Hydrophilicity and Water Contact Angle on Methylammonium Lead Iodide

“…The situation is different for MAPI, which is known to (reversibly) transform into hydrates when exposed to humidity and (irreversibly) decompose in liquid water. Despite the occurrence of the above phenomena, water contact angle measurements on MAPI films have been performed and reported in previous literature: results have shown a significant time dependence, with the CA going from 40° at 5 s from the deposition to 22° after 10 min . Our experiments confirm these observations: after few minutes from the water deposition CA = CA( t ) keeps varying, and the values at long times are sample dependent and not reproducible.…”

“…Accordingly, there is an increasing number of research items focusing on increasing the hydrophobicity of MAPI via, e.g., surface functionalization. In this context, contact angle measurements have been performed on pristine and hydrophobized films to assess their wettability …”

“…If the substrate degrades, several nonequilibrium phenomena must be taken into account such as the solubilization and phase transformations of the solid. This led to ambiguous results on MAPI, with a contact angle that strongly depends on the time of measurement, calling for a detailed microscopic investigation at the origin of the variability of the measured CA.…”

Analysing the Prospects of Perovskite Solar Cells within the Purview of Recent Scientific Advancements

“…This improvement in stability is attributed to the top layer being exposed to PCBM ETL which is hydrophobic. Kim et al demonstrated the use of an edged-selectively fluorine(F) functionalized graphene nanoplatelets (EFGnPs-F) layer between PCBM and Al electrode, exhibiting improved stability; being stable for 30 days at 50% humidity [162]. This is because of the hydrophobic nature of C-F bonding protecting the perovskite layer against moisture.…”

Database-driven high-throughput study of coating materials for hybrid perovskites

“…Hybrid perovskites degrade quickly in heat, oxygen and moisture [10][11][12][13][14]. With increasing exposure to any of these destabilizing factors, the structure of the hybrid perovskite degrades and the PCE reduces concomitantly after several days or even hours [15,16]. Among the solutions that have been proposed to solve this stability and longevity problem are protective coating [17][18][19], the use of two-dimensional perovskites [20][21][22][23][24][25], and doping with small ions [14,[26][27][28][29][30].…”