Controlling the Defect Density of Perovskite Films by MXene/SnO₂ Hybrid Electron Transport Layers for Efficient and Stable Photovoltaics

Abstract

The defect control of polycrystalline perovskite films is essential for achieving an efficient and stable perovskite solar cell (PSC). However, existing methods of reducing defects suffer from their complex processes, low durability, and limited effects by using molecular materials in terms of passivation mechanisms. Herein, a hybrid film composed of SnO 2 nanoparticles/Ti 3 C 2 T x MXene nanoflakes is used as the electron transport layer (ETL) in a planar regular-structure PSC. The results indicate that by changing the Ti 3 C 2 T x /SnO 2 ratios (0−2.2 wt %) in ETLs, the film qualities of top perovskite layers are controllable, including the compactness, crystal size, surface roughness, crystallinity, optical absorption, defect density, and so forth. The defect density in perovskite films is substantially reduced from 5.65 × 10 15 to 2.25 × 10 15 cm −3 using an optimized hybrid ETL (1.4 wt %) compared with the pristine SnO 2 , while the electrical conductivity of the hybrid ETL is decreased probably due to the geometric factor of the incorporated MXene. As a result, the power conversion efficiency of PSCs is significantly increased from 16.28 to 20.35%, and the environmental stability of the unencapsulated devices is greatly improved. This work provides a facile, robust, and effective way to reduce defects in perovskite films by using emerging MXene nanomaterials and might also be useful to other perovskite-based (opto)electronic devices such as light-emitting diodes and photodetectors.

Theoretical Modeling of Perovskite–Kesterite Tandem Solar Cells for Optimal Photovoltaic Performance

“…Recently, by introducing a Ti 3 C 2 T x MXene nanoflakes to the electron transport material, SnO 2 of a single‐junction PSC, the defect density of the perovskite film was optimized. [ 36 ] However, in computational modeling studies, different device designs can be developed by altering the defect density of the absorber itself, which, in turn, influences the recombination and generation rate of carriers and their life time. Defect density of the material, the capture cross section of the carrier, and their thermal velocity influence the diffusion length of the absorber materials also.…”

Recent progress in use of MXene in perovskite solar cells: for interfacial modification, work-function tuning and additive engineering

“…This resulted in an increase in PCE from 16.28 to 20.35% along with higher environmental stability. 144…”

“…This resulted in an increase in PCE from 16.28 to 20.35% along with higher environmental stability. 144 Yang et al prepared a nanoscale heterostructure of 2D MXene Ti 3 C 2 T x with SnO 2 by modifying its terminal groups and regulated oxidation, and used it as an ETL in PSCs. During oxidation the Ti 3 C 2 T x changed its character from metallic to semiconductor.…”

Recent advances in the interfacial engineering of organic–inorganic hybrid perovskite solar cells: a materials perspective

“…are often used to enhance the shape and crystallinity of perovskite materials and enhance charge extraction from the perovskite to the ETL because of their superior optical, electrical, thermodynamic, physical, and catalytic properties. [62][63][64] It is worth mentioning that a new member of the 2D material family, i.e., MXenes, which have a layered structure formed via selective hydrofluoric acid (HF) or in situ-induced HF corrosion of A (Al, Sn, etc.) layers of the MAX phase (laminated carbides and nitrides with a hexagonal closed-packing structure), which possess a higher electrical conductivity than the reduced graphene oxide as well as a lower absorbance in the visible-light range.…”

“…are often used to enhance the shape and crystallinity of perovskite materials and enhance charge extraction from the perovskite to the ETL because of their superior optical, electrical, thermodynamic, physical, and catalytic properties. 62–64 It is worth mentioning that a new member of the 2D material family, i.e. , MXenes, which have a layered structure formed via selective hydrofluoric acid (HF) or in situ -induced HF corrosion of A (Al, Sn, etc. )…”