Water-Repellent Low-Dimensional Fluorous Perovskite as Interfacial Coating for 20% Efficient Solar Cells

Abstract

Hybrid perovskite solar cells have been capturing an enormous research interest in the energy sector due to their extraordinary performances and ease of fabrication. However, low device lifetime, mainly due to material and device degradation upon water exposure, challenges their near-future commercialization. Here, we synthesized a new fluorous organic cation used as organic spacer to form a low-dimensional perovskite (LDP) with an enhanced water-resistant character. The LDP is integrated with three-dimensional (3D) perovskite absorbers in the form of MAFAPbI (FA = NHCH = NH, MA = CHNH) and CsFAMAPbIBr In both cases, a LDP layer self-assembles as a thin capping layer on the top of the 3D bulk, making the perovskite surface hydrophobic. Our easy and robust approach, validated for different perovskite compositions, limits the interface deterioration in perovskite solar cells yielding to >20% power conversion efficient solar cells with improved stability, especially pronounced in the first hours of functioning under environmental conditions. As a consequence, single and multijunction perovskite devices, such as tandem solar cells, can benefit from the use of the waterproof stabilization here demonstrated, a concept which can be further expanded in the perovskite optoelectronic industry beyond photovoltaics.

Two‐Dimensional Halide Perovskites in Solar Cells: 2D or not 2D?

“…Among the chemical properties that are directly influenced by the organic cation are the perovskite's solubility, thermal stability, hydrophobicity, and crystallinity (Table ). For example, the use of fluorinated cations has proven to increase the hydrophobicity and tolerance to humidity . Conversely, the composition and thickness ( n value) of the inorganic layer tend to define the optical and electronic properties of the material.…”

“…The interface between these heterostructures appears to be electronically clean and consequently it inhibits undesirable recombination assisted by trapping . 2D/3D perovskite mixtures are obtained by blending standard bulky organic cations with the 3D perovskite precursor in a one‐step spin‐coating method …”

“…Thus, the 2D perovskite layer turns the surface of the otherwise hydrophilic surface into a highly hydrophobic one, thereby improving its stability towards water. At the same time, the presence of a 2D perovskite on the 3D absorber improves the contact with the HTM, improving the overall device stability and performance (Scheme ) …”

Crystalline Clear or Not: Beneficial and Harmful Effects of Water in Perovskite Solar Cells

“…[16,29,30,31] Yang Yang and coworkers proposed in 2014 a moisture assisted grain growth of solution process perovskite materials, obtaining high crystallinity with increased grain size, carrier mobility and charge carrier lifetime, using inverted configuration devices (p-i-n) glass/ITO/PEDOT:PSS/ CH 3 NH 3 PbI 3-x Cl x /PCBM/PFN/Al. [16,29,30,31] Yang Yang and coworkers proposed in 2014 a moisture assisted grain growth of solution process perovskite materials, obtaining high crystallinity with increased grain size, carrier mobility and charge carrier lifetime, using inverted configuration devices (p-i-n) glass/ITO/PEDOT:PSS/ CH 3 NH 3 PbI 3-x Cl x /PCBM/PFN/Al.…”

“…[71] In addition to the modification of the HSL and top contact, it was also realized that the termination of the perovskite layer and its interfacial behaviour with the external contacts were determining factors. [73,31] As a final achievement, one of the recent world records of PCE 23.3 % has been obtained combining a capping layer with adequate extraction materials, leading to an adequate retention of efficiencies under ambient conditions. [72] If the CH 3 -end of MA + is pointing towards the contact surface, the water penetration was favoured with very low activation energies (0.023 eV).…”