The power conversion efficiency (PCE) of the state-of-the-art large-area slot-die-coated perovskite solar cells (PSCs) is now over 19%, but issues with their stability persist owing to significant intrinsic point defects and a mass of surface imperfections introduced during the fabrication process. Herein, the utilization of a hydrophobic all-organic salt is reported to modify the top surface of large-area slot-die-coated methylammonium (MA)-free halide perovskite layers. Bearing two molecules, each of which is endowed with anchoring groups capable of exhibiting secondary interactions with the perovskite surfaces, the organic salt acts as a molecular lock by effectively binding to both anion and cation vacancies, substantially enhancing the materials' intrinsic stability against different stimuli. It not only reduces the ingression of external species such as oxygen and moisture, but also suppresses the egress of volatile organic components during the thermal stability testing. The treated PSCs demonstrate efficiency of 19.28% (active area of 58.5 cm2 ) and 17.62% (aperture area of 64 cm2 ) for the corresponding mini-module. More importantly, unencapsulated slot-die-coated mini-modules incorporating the all-organic surface modifier show ≈80% efficiency retention after 7500 h (313 days) of storage under 30% relative humidity (RH). They also remarkably retain more than 90% of the initial efficiency for over 850 h while being measured continuously.
Extending halide perovskites' optoelectronic properties to stimuli-responsive chromism enables switchable optoelectronics, information display, and smart window applications. Here, we demonstrate a band gap tunability (chromism) via crystal structure transformation from three-dimensional FAPbBr3 to a ⟨110⟩ oriented FAn+2PbnBr3n+2 structure using a mono-halide/cation composition (FA/Pb) tuning. Furthermore, we illustrate reversible photochromism in halide perovskite by modulating the intermediate n phase in the FAn+2PbnBr3n+2 structure, enabling greater control of the optical band gap and luminescence of a ⟨110⟩ oriented mono-halide/cation perovskite. Proton transfer reaction-mass spectroscopy carried out to precisely quantify the decomposition product reveals that the organic solvent in the film is a key contributor to the structural transformation and, therefore, the chromism in the ⟨110⟩ structure. These intermediate n phases (2 ≤ n ≤ ∞) stabilize in metastable states in the FAn+2PbnBr3n+2 system, which is accessible via strain or optical or thermal input. The structure reversibility in the ⟨110⟩ perovskite allowed us to demonstrate a class of photochromic sensors capable of self-adaptation to lighting.
Metal-halide perovskites are rapidly emerging as solution-processable optical materials for light-emitting applications. Here, we adopt a plasmonic metamaterial approach to enhance photoluminescence emission and extraction of methylammonium lead iodide (MAPbI3) thin films based on the Purcell effect. We show that hybridization of the active metal-halide film with resonant nanoscale sized slits carved into a gold film can yield more than 1 order of magnitude enhancement of luminescence intensity and nearly 3-fold reduction of luminescence lifetime corresponding to a Purcell enhancement factor of more than 300. These results show the effectiveness of resonant nanostructures in controlling metal-halide perovskite light emission properties over a tunable spectral range, a viable approach toward highly efficient perovskite light-emitting devices and single-photon emitters.
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Metal halide perovskite solar cells, despite achieving high power conversion efficiency (PCE), need to demonstrate high stability prior to be considered for industrialization. Prolonged exposure to heat, light, and moisture is known to deteriorate the perovskite material owing to the breakdown of the crystal structure into its non-photoactive components. In this study, we show that by combining the organic ligand 1-naphthylmethylammoinium iodide (NMAI) with methylammonium (MA) to form a mixed dimensional (NMA)2(MA)n-1PbnI3n+1 perovskite the optical, crystallographic and morphological properties of the newly formed mixed dimensional perovskite films under thermal ageing can be retained. Indeed, under thermal ageing at 85 °C, the best performing (NMA)2(MA)n-1PbnI3n+1 perovskites films show a stable morphology, a low PbI2 formation rate and a significantly reduced variation of both MA-specific vibrational modes and fluorescence lifetimes as compared to the pristine MAPbI3 films. These results highlight the role of the bulky NMA+ organic cation in mixed dimensional perovskites to both inhibit the MA+ diffusion and reduce the material defects, which act as non-radiative recombination centres. As a result, the thermal stability of metal halide perovskites has been substantially improved.
It is well known that the surface trap states and electronic disorders in the solution-processed CH3 NH3 PbI3 perovskite film affect the solar cell performance significantly and moisture sensitivity of photoactive perovskite material limits its practical applications. Herein, we show the surface modification of a perovskite film with a solution-processable hydrophobic polymer (poly(4-vinylpyridine), PVP), which passivates the undercoordinated lead (Pb) atoms (on the surface of perovskite) by its pyridine Lewis base side chains and thereby eliminates surface-trap states and non-radiative recombination. Moreover, it acts as an electron barrier between the perovskite and hole-transport layer (HTL) to reduce interfacial charge recombination, which led to improvement in open-circuit voltage (Voc ) by 120 to 160â mV whereas the standard cell fabricated in same conditions showed Voc as low as 0.9â V owing to dominating interfacial recombination processes. Consequently, the power conversion efficiency (PCE) increased by 3 to 5 % in the polymer-modified devices (PCE=15 %) with Voc more than 1.05â V and hysteresis-less J-V curves. Advantageously, hydrophobicity of the polymer chain was found to protect the perovskite surface from moisture and improved stability of the non-encapsulated cells, which retained their device performance up to 30â days of exposure to open atmosphere (50 % humidity).
Electric Power Supplies , Polyvinyls/chemistry , Solar Energy , Calcium Compounds , Hydrophobic and Hydrophilic Interactions , Lead , Oxides , Pyridines , Surface Properties , Titanium
