2D Ruddlesden-Popper Perovskites Research Articles

A Comprehensive Study of Electronic, Optical, and Thermoelectric Characteristics of Cs2PbI2Br2 Inorganic Layered Ruddlesden-Popper Mixed Halide Perovskite through Systematic First-Principles Analysis.

In this research, we present a comprehensive study on the influence of layer-dependent structural, electronic, and optical properties in the two-dimensional (2D) Ruddlesden-Popper (RP) perovskite Cs2PbI2Br2. Employing first-principles computations within the density functional theory method, including spin orbit coupling contribution, we examine the impact of various factors on the material. Our results demonstrate that the predicted 2D-layered RP perovskite Cs2PbI2Br2 structures exhibit remarkable stability both structurally and energetically, making them promising candidates for experimental realization. Furthermore, we observe that the electronic band gap and optical absorption coefficients of Cs2PbI2Br2 strongly depend on the thickness variation of the layers. Interestingly, Cs2PbI2Br2 exhibits a notable absorption coefficient in the visible region. Using a combination of density functional theory and Boltzmann transport theory, the thermoelectric properties were forecasted. The calculation involved determining the Seebeck coefficient (S) and other associated thermoelectric characteristics, such as electronic and thermal conductivities, as they vary with the chemical potential at room temperature. These findings open up exciting opportunities for the application of this 2D RP perovskite in solar cells and thermoelectric devices, owing to its unique properties.

Selenophene-Based 2D Ruddlesden-Popper Perovskite Solar Cells with an Efficiency Exceeding 19.

Two-dimensional (2D) Ruddlesden-Popper (RP) perovskites have emerged as attractive candidates for high-performance perovskite solar cells (PSCs) thanks to their superior environmental and structural stability. However, 2D RP PSCs exhibit larger exciton binding energy due to the dielectric mismatch between the organic and inorganic layers, resulting in poorer photovoltaic performance compared to their 3D analogs. Here, we developed a selenophene-based spacer, namely, 2-selenophenemethylammonium (SeMA), for stable and efficient 2D RP PSCs. The 2D perovskite film using methylammonium (MA) as the A-site cation (nominal n = 5) shows excellent film quality with large grain size and a preferred vertical orientation relative to the substrate. Furthermore, we have successfully demonstrated the effectiveness of a predeposition transport layer (PDTL) consisting of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) in passivating surface defects of the perovskite film and inducing densification of the upper PCBM electron transport layer. This densification promotes efficient extraction and transport of electrons. The optimized PSCs based on 2D RP perovskite using MA as A-site cation (nominal n = 5) achieved a power conversion efficiency (PCE) of 17.25%, which was further boosted to 19.03% when using formamidinium (FA) as A-site cation. This represents a record PCE of 2D RP PSCs by using the selenophene-based spacer. Moreover, these 2D RP PSCs significantly improve thermal, moisture, and light stability. Our results provide significant implications for the synergistic strategy of developing selenophene-based spacers and device engineering methods for achieving highly efficient and stable 2D RP perovskite solar cells.

Regulation of phase arrangement in 2D ruddlesden-popper perovskite films via anti-solvent method for efficient solar cells

Recently, quasi-two-dimensional RP(Ruddlesden-Popper)-based perovskite solar cells have attracted a wide range of research interest. However, two-dimensional layered perovskites have disordered phase distribution and multi-quantum well structure that are adversely to charge transport and extraction, resulting in the inability to obtain relatively satisfactory photoelectric conversion efficiency (PCE). Here, we fabricated an 2D RP perovskite solar cell with reversely graded phase arrangement by friendly antisolvent method, and obtained the PCE of 14.45%. The dependence of efficiency on device architecture according to the vertical growth direction is further revealed and discussed. To investigate the effect of different antisolvents on crystal orientation and phase arrangement of GA-based 2D RP perovskites, we applied IPA as antisolvent and found that IPA not only significantly improved the surface roughness, quality and crystallinity of 2D perovskites but also reduce or even eliminate lower-n (n = 1, 2) phases and improve the vertical orientation of 2D phases in perovskites films, thereby improving charge transport and extraction. In the end, we achieved a champion PCE of 15.80%. These findings provide an effective guidance for developing GA-based organic spacers toward highly efficient and stable 2D PSCs with less quantum confinement.

Systematic first-principles investigation of electronic, optical and thermoelectric properties of all-inorganic layered ruddlesden-popper mixed halide perovskite Cs2SnI2Br2

Report on systematic study of the impact of layer dependent structural properties, electronic structures and optical characteristics on the two-dimensional (2D) Ruddlesden–Popper (RP) perovskite Cs2SnI2Br2 using first principles computation within the density functional theory method including a spin orbit coupling contribution. Our results reveal that the predicted 2D-layered RP perovskite Cs2SnI2Br2 are structurally and energetically stable which can be realized in experiments. It is also shown that the band gap and optical absorption characteristics of the 2D-layered RP perovskite Cs2SnI2Br2 are dependent on thickness variation. Interestingly, Cs2SnI2Br2 exhibited an interesting absorption coefficient in the visible region. The transport equations were solved in order to evaluate the effect of the Sn based 2D-layered RP perovskite on thermoelectric performance. It is found that Cs2SnI2Br2 has lower thermal conductivity and higher electrical conductivity for T = 300 K. In addition, Cs2SnI2Br2 is expected to get the highest figure of merit. This result provides an outstanding opportunity for this 2D RP perovskite with potential applications in solar cells and thermoelectric applications.

Halide Ion Mixing across Colloidal 2D Ruddlesden-Popper Perovskites: Implication of Spacer Ligand on Mixing Kinetics.

Halide ion exchange seen in metal halide perovskites provide a substantial opportunity to control their halide composition and corresponding optoelectronic properties. Halide ion mixing across colloidal 3D perovskite nanocrystals have been extensively studied while the mixing within colloidal 2D counterparts remain underexplored. In this study, the halide ion exchange kinetics across colloidally stable 2D Ruddlesden-Popper layered bromide (Br) and iodide (I) perovskites using two different spacer ligands such as aromatic phenethylammonium (PEA) versus linear butyammonium (BA) is demonstrated. The halide exchange kinetic rate constant (k), as determined by tracking time-dependent absorbance changes, indicates that Br/I halide mixing in 2D PEA-based perovskites (2.7 × 10-3 min-1 ) occurs at an order of magnitude slower than in 2D BA-based perovskites (3.3 × 10-2 min-1 ). Concentration (≈1mM to 100mM) and temperature-dependent (50 to 80 °C) kinetic studies further allow for the determination of activation barrier for halide ion mixing across the 2D layered perovskites with 75.2 ± 4.4kJ mol-1 (2D PEA) and 57.8 ± 7.8kJ mol-1 (2D BA), respectively. The activation energy reveals that the type of spacer cations plays a crucial role in controlling the halide ion mobility and halide stability due mainly to the internal ligand chemical interaction within 2D structures.

Highly Stable and Efficient Formamidinium-Based 2D Ruddlesden-Popper Perovskite Solar Cells via Lattice Manipulation.

Formamidinium (FA)-based 2D perovskites have emerged as highly promising candidates in solar cells. However, the insertion of 2D spacer cations into the perovskite lattice concomitantly introduces microstrain and unfavorable orientations that hinder efficiency and stability. In this study, by finely tuning the FA-based 2D perovskite lattice through spacer cation engineering, a stable lattice structure with balanced distortion, microstrain relaxation, and reduced carrier-lattice interactions is achieved. These advancements effectively stabilize the inherently soft lattice against light and thermal-aging stress. To reduce the photocurrent loss induced by undesired crystal texture, a polarity-matched molecular-type selenourea (SENA) additive is further employed to modulate the crystallization kinetics. The introduction of the SENA significantly inhibits the disordered crystallization induced by spacer cations and drives the templated growth of the quantum well structure with a vertical orientation. This controlled crystallization process effectively reduces crystal defects and enhances charge separation. Ultimately, the optimized FA-based perovskite photovoltaic devices achieve a remarkable power conversion efficiency (PCE) of 20.03% (certified steady-state efficiency of 19.30%), setting a new record for low-n 2D perovskite solar cells. Furthermore, the devices exhibit less than 1% efficiency degradation after operating at maximum power point for 1000 h and maintain excellent stability after thermal aging and cycles of cold-warm shock, respectively.

X-Site Substituted 2D Cs2 Pb(SCN)2 Br2 Perovskites for X-Ray Detection.

2D Ruddlesden-Popper (RP) perovskites have been intensively investigated due to their superior stability and outstanding optoelectrical properties. However, investigations on 2D RP perovskites are mainly focused on A-site substituted perovskites and few reports are on X-site substituted perovskites especially in X-ray detection field. Here, X-site substituted 2D RP perovskite Cs2 Pb(SCN)2 Br2 polycrystalline wafers are prepared and systematically studied for X-ray detection. The obtained wafers show a large resistivity of 2.0 × 1010 Ω cm, a high ion activation energy of 0.75eV, a small current drift of 2.39 × 10-6 nA cm-1 s-1 V-1 , and charge carrier mobility-lifetime product under X-ray as high as 1.29 × 10-4 cm2 V-1 . These merits enable Cs2 Pb(SCN)2 Br2 wafer detectors with a sensitivity of 216.3 µC Gyair -1 cm-2 , a limit of detection of 42.4 nGyair s-1 , and good imaging ability with high spatial resolution of 1.08 lp mm-1 . In addition, Cs2 Pb(SCN)2 Br2 wafer detectors demonstrate excellent operational stability under high working field up to 2100V cm-1 after continuous X-ray irradiation with a total dose of 45.2 Gyair . The promising features such as short octahedral spacing and weak ion migration will open up a new perspective and opportunity for SCN-based 2D perovskites in X-ray detection.

Spatial Heterogeneity of Biexcitons in Two-Dimensional Ruddlesden-Popper Lead Iodide Perovskites.

Quantum confinement in two-dimensional (2D) Ruddlesden-Popper (RP) perovskites leads to the formation of stable quasi-particles, including excitons and biexcitons, the latter of which may enable lasing in these materials. Due to their hybrid organic-inorganic structures and the solution phase synthesis, microcrystals of 2D RP perovskites can be quite heterogeneous, with variations in excitonic and biexcitonic properties between crystals from the same synthesis and even within individual crystals. Here, we employ one- and two-quantum two-dimensional white-light microscopy to systematically study the spatial variations of excitons and biexcitons in microcrystals of a series of 2D RP perovskites BA2MAn-1PbnI3n+1 (n = 2-4, BA= butylammonium, MA = methylammonium). We find that the average biexciton binding energy of around 60 meV is essentially independent of the perovskite layer thickness (n). We also resolve spatial variations of the exciton and biexciton energies on micron length scales within individual crystals. By comparing the one-quantum and two-quantum spectra at each pixel, we conclude that biexcitons are more sensitive to their environments than excitons. These results shed new light on the ways disorder can modify the energetic landscape of excitons and biexcitons in RP perovskites and how biexcitons can be used as a sensitive probe of the microscopic environment of a semiconductor.

Reversible and Irreversible Layer Edge Relaxation in Laser‐Radiation‐Hardened 2D Organic–Inorganic Perovskite Crystals

The layer edge states or low energy state (LES) in 2D hybrid organic–inorganic perovskites demonstrate a prolonged carrier lifetime for better performance of optoelectronic devices. However, the fundamental understanding of LES in 2D perovskites is still inconclusive. Herein, a photoluminescence (PL) study of LES in 2D Ruddlesden–Popper perovskites is presented with n = 2 and n = 3 from their cleaved cross sections that are more stable than the natural edge. The PL measurements clearly observe reversible, and irreversible surface relaxations (case I and case II) in three laser intensity ranges, further supported by a PL excitation cycle from low to high laser intensity, and vice versa. The PL wavelength of LES is tunable with laser intensity and blueshifts with increasing laser intensity during irreversible surface relaxation process (case I). Fluorescence lifetime imaging (FLIM) shows that the LES has a longer lifetime than the band‐edge emission in the sample without a photodegradation, while the BE lifetime becomes relatively longer in the area with a photodegradation. The presented laser tunable LES and the related irreversible relaxation process provide a new insight that can help improve the photostability in 2D perovskites and understand roles of LESs in optoelectronic device performance.

Cellulose‐Assisted Formation of 2D Hybrid Halide Perovskite Nanocrystals with Enhanced Stability for Light‐Emitting Devices

AbstractA common approach to enhance the stability of metal halide perovskites (MHPs) implemented in optical and optoelectronic devices is to incorporate polymer additives into the perovskite layer. A β‐(1,4) cellulose oligosaccharide (COS) synthesized by mechanocatalytic depolymerization of cellulose has been incorporated to films of the BA2MA4Pb5I16 (BA = n‐butylammonium and MA = methylammonium) two‐dimensional (2D) Ruddlesden‐Popper (RP) hybrid perovskite. Scanning Electron Microscopy (SEM) images displayed a three‐fold reduction of the 2D RP perovskite grains (≈30–40 nm), close to the quantum confinement scale. The analysis of the dark J–V curves of single carrier devices by using the space charge limited current (SCLC) method resulted in a rise of the defect concentration. A notable 14‐fold increase in the photoluminescence (PL) signal at high COS content is detected. Moreover, the analysis of the temperature dependence PL measurements (80–300 K) resulted in a larger exciton binding energy, Eb = 180 to 370 meV, at high COS content. Light emitting diodes of the 2D RP perovskites (PeLEDs) are fabricated w/o the COS compound. The stability test performed under operation (5 V) displays 20 times higher operational lifetimes at high COS content while the luminance is also increased in the devices with the COS compound.

Synergistic Passivation With Phenylpropylammonium Bromide for Efficient Inverted Perovskite Solar Cells.

Inverted perovskite solar cells (PSCs) are a promising technology for commercialization due to their reliable operation and scalable fabrication. However, in inverted PSCs, depositing a high-quality perovskite layer comparable to those realized in normal structures still presents some challenges. Defects at grain boundaries and interfaces between the active layer and carrier extraction layer seriously hinder the power conversion efficiency (PCE) and stability of these cells. In this work, it is shown that synergistic bulk doping and surface treatment of triple-cation mixed-halide perovskites with phenylpropylammonium bromine (PPABr) can improve the efficiency and stability of inverted PSCs. The PPABr ligand is effective in eliminating halide vacancy defects and uncoordinated Pb2+ ions at both grain boundaries and interfaces. In addition, a 2D Ruddlesden-Popper (2D-RP) perovskite capping layer is formed on the surface of 3D perovskite by using PPABr post-treatment. This 2D-RP perovskite capping layer possesses a concentrated phase distribution ≈n = 2. This capping layer not only reduces interfacial non-radiative recombination loss and improves carrier extraction ability but also promotes stability and efficiency. As a result, the inverted PSCs achieve a champion PCE of over 23%, with an open-circuit voltage as high as 1.15V and a fill factor of over 83%.

Pinhole-free 2D Ruddlesden–Popper perovskite layer with close packed large crystalline grains, suitable for optoelectronic applications

Here, we achieved pinhole-free 2D Ruddlesden–Popper Perovskite (RPP) BA2PbI4 layers with close packed crystalline grains with dimension of about 30 × 30 µm2, which have been demonstrated to be favorable for optoelectronic applications, such as fast response RPP-based metal/semiconductor/metal photodetectors. We explored affecting parameters in hot casting of BA2PbI4 layers, and proved that oxygen plasma treatment prior to hot casting plays a significant role to achieve high quality close packed polycrystalline RPP layers at lower hot cast temperatures. Moreover, we demonstrate that crystal growth of 2D BA2PbI4 can be dominantly controlled by the rate of solvent evaporation through substrate temperature or rotational speed, while molarity of the prepared RPP/DMF precursor is the dominant factor that determines the RPP layer thickness, and can affect the spectral response of the realized photodetector. Benefiting from the high light absorption and inherent chemical stability of 2D RPP layers, we achieved high responsivity and stability, and fast response photodetection from perovskite active layer. We achieved a fast photoresponse with rise and fall times of 189 µs and 300 µs, and the maximum responsivity of 119 mA/W and detectivity of 2.15 × 108 Jones in response to illumination wavelength of 450 nm. The presented polycrystalline RPP-based photodetector benefits from a simple and low-cost fabrication process, suitable for large area production on glass substrate, a good stability and responsivity, and a promising fast photoresponse, even around that of exfoliated single crystal RPP-based counterparts. However, it is well known that exfoliation methods suffer from poor repeatability and scalability, which make them incompatible with mass production and large area applications.

Efficient Narrowband Photoconductivity of the Excitonic Resonance in Two-Dimensional Ruddlesden-Popper Perovskites Due to Exciton Polarons.

Filter-less, wavelength-selective photodetectors made of perovskite usually rely on the charge collection narrowing mechanism, which intrinsically limits the response times. Using the narrow excitonic peak of, e.g., two-dimensional (2D) Ruddlesden-Popper perovskites as direct absorbers to realize color-selective photodetectivity promises faster responses. However, one major challenge in realizing such devices remains the separation and charge carrier extraction of the tightly bound excitons. Here, we report on filter-less color-selective photoconductivity in 2D perovskite butylammonium lead iodide thin film devices, exhibiting a distinct resonance in the photocurrent spectrum with a full width at half-maximum of 16.5 nm that correlates to the excitonic absorption. Our devices exhibit unexpectedly efficient charge carrier separation with an external quantum efficiency of ≤8.9% at the excitonic resonance, which we trace back to the involvement of exciton polarons. Our photodetector achieves response times of 150 μs and a maximum specific detectivity of 2.5 × 1010 Jones at the excitonic peak.

Bulk Incorporation of Molecular Dopants into Ruddlesden–Popper Organic Metal–Halide Perovskites for Charge Transfer Doping

AbstractOrganic metal‐halide perovskites (OHPs) have recently attracted much attention as next‐generation semiconducting materials due to their outstanding opto‐electrical properties. However, OHPs currently suffer from the lack of efficient doping methods, while the traditional method of atomistic doping having clear limitations in the achievable doping range. While doping with molecular dopants, has been suggested as a solution to this problem, the action of these dopants is typically restricted to perovskite surfaces, therefore significantly reducing their doping potential. In this study, successful bulk inclusion of “magic blue”, a molecular dopant, into 2D Ruddlesden–Popper perovskites is reported. This doping strategy of immersing the perovskite film in dopant solution increases the electrical current up to ≈60 times while maintaining clean film surface. A full mechanistic picture of such immersion doping is provided, in which the solvent molecule facilitates bulk diffusion of dopant molecule inside the organic spacer layer. Physical criteria for judicious choice of solvents in immersion doping are developed based on readily available solvent properties. The immersion doping method developed in this study that enables bulk molecular doping in OHPs will provide a strategic doping methodology for controlling electrical properties of OHPs for electronic and optoelectronic devices.

High‐Quality Lead Acetate–Based Ruddlesden–Popper Perovskite Films for Efficient Solar Cells

The 2D Ruddlesden–Popper perovskites (RPPs), consisting of alternating organic spacer layers and inorganic layers, are emerging photovoltaic materials because of their highly tunable optoelectronic properties and improved stability compared to their 3D counterparts. Nonhalide lead sources attract increasing attention in 3D perovskites, whereas the lead sources for RPPs are limited to lead halides. Herein, nonhalide lead source of lead acetate is investigated for high‐quality RPP films by a dimethyl sulfoxide (DMSO)‐assisted delayed annealing process. The incorporation of DMSO in the lead acetate–based precursor solution regulates the crystallization process, resulting in RPP films with distinctly enhanced crystallinity, reduced trap density, vertical crystal orientation, and graded phase distribution. Consequently, the optimized RPP solar cell with an inverted planar structure delivers a champion power conversion efficiency of 17.3%. Herein, future developments of nonhalide lead sources are spurred to fabricate RPP films with high device performance.

Controllable Synthesis of Centimeter-Sized 2D Ruddlesden–Popper Perovskite Single Crystals through Intermediate-Phase Engineering

Controllable Synthesis of Centimeter-Sized 2D Ruddlesden–Popper Perovskite Single Crystals through Intermediate-Phase Engineering

Controllable Transformation of 2D Perovskite for Multifunctional Sensing Properties

There is growing demand for convenient and cost-efficient ethanol sensing techniques in daily life and industry. However, the complexity, high cost, and large volume of the equipment hinder the widespread use of conventional ethanol sensing techniques. Here, we introduce a test paperlike visualized label-free ethanol sensing platform by taking advantage of the instability of 2D Ruddlesden–Popper perovskite in ethanol. The photoluminescence of PEA2Csn–1PbnBr3n+1 2D perovskite changes from deep blue to green distinctly when exposed to ethanol. A cheap demo ethanol test paper is fabricated by this 2D perovskite and paper using a simple method, demonstrating interesting rapid and convenient ethanol sensing performance. Crystal analysis, constituent analysis, spectral analysis, and molecular dynamic (MD) simulation reveal the crystal structure transformation from 2D to 3D induced by the migration of PEA+ cations in the original 2D perovskite when exposed to ethanol. In addition, a chemiresistive sensor based on the 2D perovskite and on the 2D–3D phase transformation is developed and demonstrates a high ethanol detection sensitivity with a limit down to 0.7 ppm. The photodetector fabricated by the 2D perovskite also demonstrates tunable sensitivity upon the controllable 2D–3D transformation. This remarkable colorimetric, chemiresistive, and photosensitive perovskite is expected to highlight its future application and be a supplement to the existing ethanol sensing and photodetector techniques.

Strained induced metallic to semiconductor transitions in 2D Ruddlesden Popper perovskites: A GGA + SOC approach

Based on RP perovskites, we put 2%, 4%, 6%, and 8% biaxial strains on 2D monolayers of phenyl-ammonium tin iodide (PH2SnI4) perovskites. Density functional theory (DFT) is used to study the structural distortion, octahedral tilting, band gap tuning, Bader charge analysis, and mechanical stability of the resulting configurations. Band gaps under the effects of compressive strain (Eg1), zero strain (Eg2), and tensile strain (Eg3) follow a decreasing order of Eg1(1.262 eV) < Eg2(1.329 eV) < Eg3(1.331 eV) for 6%-strain. The absence of trap states in energy band gaps and dominant cation and anion contributions at conduction and valence band edges supports the defect tolerance. All the structures analyzed are mechanically stable. The covalently bonded structures are ductile/brittle under tensile/compressive strain, with a prominent stretching mode. Strain improves the optical performance with dielectric constant increased (red-shifted) under compressive strain and reduced (blue-shifted) under compressive strain.

Stereopsis-Inspired 3D Visual Imaging System Based on 2D Ruddlesden-Popper Perovskite.

Stereopsis is of great important functions for humans to perceive and interact with the world. To realize the function of stereoscopic imaging, optoelectronic sensors shall possess good photoresponsive performance, multidirectional sensing, and 3D building capabilities. However, the current imaging sensors are mainly focused on 2D imaging, limiting their practical application scenarios. In this study, a stereopsis-inspired flexible 3D visual imaging system (VIS) based on 2D Ruddlesden-Popper perovskite is demonstrated. The 3D-VIS consists of 800 device units, each of which demonstrates excellent photoresponse performance, mechanical characteristics, and environmental stability. In addition to the capability of detecting 2D reflective images, the 3D-VIS realizes the function of detecting the depth of field and fusing object projections of two directions to invert the 3D image by utilizing voxels to rebuild the spatial structure of the object. In the future, the 3D-VIS will have broad application prospects in medical imaging, virtual reality, industrial automation, and other fields.

Construction of a 3D/2D heterojunction based on a fluorinated cyclohexylamine 2D Ruddlesden–Popper perovskite for highly efficient and stable perovskite solar cells

Nonradiative recombination at perovskite/charge transport layer interfaces is caused by surface defects and instability, and it is known to limit the long-term development of perovskite solar cells (PSCs). To overcome this issue, the three-dimensional/two-dimensional (3D/2D) perovskite heterojunction has emerged as a possible solution to improve the stabilities and efficiency of PSCs. Herein, we employ a simple one-step method to prepare n-i-p-structured PSCs using a 3D/2D perovskite heterojunction as the absorption layer. For this purpose, the large and non-centrosymmetric 4,4-difluorocyclohexylammonium (DFCHA+) cation, which has been confirmed to be a valid organic spacer in 2D Ruddlesden–Popper (RP) phase perovskites, is employed as an organic ligand for post-treatment of the surfaces of MAPbI3 films. The presence of an ultrathin 2D RP phase perovskite was confirmed on the surface, and the 3D/2D perovskite heterojunction was successfully constructed. Benefitting from surface post-treatment, the density of the surface trap states was reduced with effective passivation. In addition, nonradiative recombination was suppressed, and the interface bands were aligned. As a result, the optimal device achieved a power conversion efficiency of 21.93% with a remarkable open-circuit voltage (VOC) of 1.14 V, a current density (JSC) of 23.71 mA cm−2, and a fill factor of 0.82. Furthermore, owing to the hydrophobicity of the DFCHA+ cation, the unencapsulated device was able to maintain an initial efficiency of 82.3% after storage for 500 h at a relative humidity of ∼45%. We believe that this post-treatment strategy has wide application potential in the field of photovoltaic devices.