Mixed Halide Perovskite Research Articles

Chemical Synergic Stabilization of High Br-Content Mixed-Halide Wide-Bandgap Perovskites for Durable Multi-Terminal Tandem Solar Cells with Minimized Pb Leakage.

High Br-content mixed-halide perovskites with wide-bandgap (WBG) of 1.6-2.0 eV have showcased vast potential to be used in tandem solar cells. However, they often suffer from severe halide segregation, phase separation and ion migration issues, which would accelerate the decomposition of perovskites films,deteriorate the photovoltaic performance and even aggravate the lead leakage from damaged devices. Here, we report a novel chemical synergic interaction strategy to mitigate the abovementioned issues. A small amount of cationic β-cyclodextrin, composed of multiple ammonium cations, chlorine ions and abundant hydroxyl functional groups, was introduced into WBG perovskites, which effectively stabilized the halide ions and homogenized the phase distribution, comprehensively passivated the defects,and efficiently immobilized the Pb2+ ions. Encouragingly, the cationic β-cyclodextrin was universal and useful for different WBG perovskites, which favorably boosted the efficiencies by 10%-36% and extended the device operational stability to 2680 h. The integrated four-terminal orsix-terminal all-perovskite tandem solar cells exhibited efficiencies up to 24.39% and 22.42%, respectively. We demonstrated the cationic β-cyclodextrin-assisted internal chemical encapsulation effectively prevented the Pb leakage from severely damaged devices with only 5.63 ppb Pb leaching out. The target tandem solar cells with cationic β-cyclodextrin modification also realized a Pb sequestration efficiency of 93.4%.

Alder-Ene Reaction-Mediated Suppression of Tin(II) Oxidation for Efficient Tin-Lead Perovskite Solar Cells.

Despite numerous studies have reported the inhibition of tin (II) oxidation in mixed tin-lead halide perovskite, there remains a dearth of mechanistic information regarding how tin (II) undergoes oxidation in the precursor solution, particularly in terms of the involvement of DMSO. We here take advantage of density functional theory (DFT) to uncover that SnI2 can coordinate with DMSO and react with singlet oxygen, resulting in the generation of Sn (IV). Moreover, our DFT simulations reveal that benzaldehyde oxime (BZHO) competes with SnI2 in reacting with oxygen through the Alder-ene reaction, hence effectively restraining the oxidation of tin (II), which is further verified by several experimental characterizations. Besides, the introduction of BZHO has also regulated the crystallization of the perovskite film and modified the electronic structure of the perovskite surface. As a result, the perovskite solar cells with the addition of BZHO demonstrate superior performance and operational stability, retaining 82 % of the initial PCE under continuous 1-sun illumination for 800 hours. Furthermore, the efficiency of all-perovskite tandem solar cells treated with BZHO reached 26.76 %. Therefore, this work presents a promising strategy for designing high-performance and stable all-perovskite tandem solar cells.

Excitonic properties and solar harvesting performance of Cs2ZnY2X2 as quasi-2D mixed-halide perovskites

Due to their low toxicity and high-temperature stability, lead-free quasi-2D metal halide perovskites (MHPs) are promising materials for optoelectronic applications. However, understanding their structural and optoelectronic properties, especially excitonic effects (electron-hole pair, e-h), is challenging due to their quantum well topology. We propose an efficient protocol for band gap correction of Cs2ZnX (X = Cl4, Br2Cl2, and I2Cl2) and Cs2PbI2Cl2 (used as a benchmark) quasi-2D MHPs. This protocol is based on a relativistic quasiparticle approach (DFT-1/2) using density functional theory (DFT). We first examined the hybrid contributions of the halide alloys, leading to excitonic characterization using the Bethe–Salpeter equation within the maximally localized Wannier functions tight-binding method. This method provides a cost-effective approach for describing e-h quasiparticle effects. Additionally, we analyzed the crystal structure, thermodynamic stability, and optoelectronic properties of the newly synthesized Zn-based systems, focusing on their structural stability mechanisms. We found a correlation between the allocation of Cs+ cations in the crystal structure and the formation of two distinct stabilization patterns, influenced by the radii of the metal (Zn or Pb) and halide components. The relativistic correction of the band gap energies yielded results within 10 % of the experimental values. Furthermore, incorporating e-h quasiparticle effects for Cs2PbI2Cl2 resulted in an exciton binding energy of 0.160 eV, in excellent agreement with experimental data. This work represents a significant advance in the optoelectronic characterization of Cs2ZnX systems, previously unexplored for their excitonic properties.

Development of a self-powered mixed halide perovskite-based planar near-ultraviolet photodetector by leveraging the pyro-phototronic effect

Self-powered devices enabled by pyro-phototronic effect (PPE) in mixed halide perovskites was investigated, diverging from conventional approaches that focus on ferroelectric materials and single-halide compositions. The compound (C4H9NH3)2PbI2Br2 was utilized to develop, a simple planar device structure that demonstrated high detectivity in the near-ultraviolet (UV). The proposed device successfully detected photocurrent signals at zero bias voltage in the 405 nm and 532 nm wavelengths, thereby confirming the feasibility of a self-powered photodetector. Notably, the study reveals a significant enhancement in photocurrent, with an increase of up to 23 % at 405 nm, driven by the combined effects of PPE and photovoltaics phenomena present in mixed halide perovskites. These findings present a promising pathway for advancing the design and fabrication of near-UV optoelectronic photodetectors and related devices.

Effect of lanthanum doped SnO2 on the performance of mixed-cation mixed-halide perovskite layer

Perovskite solar cells (PSCs) have attracted significant attention due to their higher efficiencies and lower fabrication costs. But for the better performance of PSCs, a high-quality electron transport layer (ETL) is crucial. Various ETLs have been employed and among them Tin (IV) oxide (SnO2) has emerged as a promising candidate for electron selective layer in PSCs due to its superior optical and electrical characteristics. However, there is still improvement needed in terms of poor surface morphology and conductivities of SnO2. When SnO2 is used in conjunction with absorber layer in ambient conditions, stability, and charge carrier recombinations at SnO2/perovskite interface remains a serious challenge as well. This study presents the doping of lanthanum (La III), a rare earth element, into SnO2 ETLs to improve the quality and performance of the perovskite layer deposited on top of ETL in ambient condition. With the optimized 4% La (III) doping, SnO2 ETLs become more crystalline with lower parasitic light absorption and surface morphology improves significantly. The improvement in morphology due to doping facilitates larger crystal growth of perovskite in ambient environment. Moreover, Photoluminescence reveals that with optimized level of doping, interfacial charge recombinations are significantly mitigated ensuring smooth injection of electrons into ETL because of superior perovskite film quality. The mixed-cation mixed-halide perovskite film deposited on 4% La:SnO2 ETL show better resistance towards moisture ingress and will substantially contribute to develop long-life of planar PSCs.

Energy-band gradient structure originated from longitudinal phase segregation of mixed halide perovskite single crystal

Energy-band gradient halide perovskites are highly desired candidates for fabricating high performance optoelectronic devices. Here, we demonstrate that a mixed halide perovskite single crystal undergoes phase segregation in the longitudinal direction under above-bandgap light illumination. As a result, a micron thick layer with vertically gradient halide composition and thus graded valence band edge is generated at the crystal surface. The resultant gradient structure can facilitate the hole extraction at its interface with a hole transport layer. The longitudinal phase segregation of mixed halide perovskite single crystal is likely driven by abundant defects at the surface. Moreover, the segregation rate is increased in air compared to nitrogen probably due to the combined effect of oxygen and moisture. These findings not only deepen the understanding of phase segregation mechanism in mixed halide perovskite, but also indicate a promising avenue of fabricating vertically energy-band gradient perovskite and enhancing the perovskite-based optoelectronic device performance.

(Invited) Perovskite/Perovskite Tandem Photoelectrodes for Unassisted Water Splitting

The bandgap tunability and low-temperature processing make halide perovskites excellent candidates for achieving efficient and cost-effective tandem devices for solar cells and solar-driven water electrolysis devices. Here, we report our progress on fabricating perovskite/perovskite tandem cells consisting of two solution-processed perovskite subcells for unassisted water-splitting applications. The perovskite/perovskite tandem photoelectrodes are achieved by monolithically integrating a wide-bandgap (1.7 – 2.1 eV) Pb-based mixed-halide (Br-I) perovskite top subcell and a narrower-bandgap (1.25 - 1.55 eV) bottom subcell based on Pb-based or mixed Pb-Sn iodide perovskites. Varying the halide perovskite composition for each subcell enables us to tailor the photovoltaic performance of the tandem devices. We demonstrate that perovskite/perovskite tandem solar cells can deliver open-circuit voltages of more than 2 V. The high photovoltage provides a sufficient overpotential to drive unassisted photoelectrochemical (PEC) water splitting with a solar-to-hydrogen conversion efficiency of more than 15%. After applying water-impermeable encapsulants, the perovskite/perovskite photoelectrodes can successfully operate in an aqueous environment and enable a long operational lifetime.

Thiourea-Induced Cocrystallization of Mixed-Halide Perovskite Thin Films for High-Performance Pure Blue Perovskite Light Emitting Diodes

Metal halide perovskite light-emitting diodes (PeLEDs) are gaining significant attention towards next-generation display materials owing to their advantageous properties, including color tunability, exceptionally narrow bandwidth, and high luminescence. Recent studies have successfully achieved over 20% external quantum efficiencies (EQE) in green and red PeLEDs. However, the blue PeLEDs lag far behind those of green or red PeLEDs because unstable phase stability in mixed halide perovskite thin films under high turn-on voltage (Von). In specific, the blue emission usually possesses halide ions with smaller ionic radius (Cl- or Br-), which easily migrates under high operative bias generating significant halogen vacancies and phase-transformation. In this context, we suggest thiourea as a promising additive for stabilizing defective perovskite thin films. Thiourea is a well-known hydrogen bond donor to halogens, which allows potential coordination complex of thiourea-halide ions to encompass well-dispersed mixed halides in co-crystallized perovskite lattices. In addition, the strong coordination of the C=S···Pb2+ was also demonstrated the thiourea-incorporated perovskite films, which effectively passivated undercoordinated Pb2+ antisites. Consequently, the thiourea-incorporated perovskite films exhibited stable deep-blue emission within 460 nm, demonstrating excellent luminance and quantum efficiency in pure blue PeLEDs. Moreover, the addition of thiourea achieved decreased Von and excellent spectral stability of pure blue PeLEDs at high applied bias, leading to significant advancements in pure blue perovskite display technology.

(Invited) Ion Migration Influencing Perovskite Solar Cell Performance and Stability

The thermodynamic and redox properties of halide perovskites provide a strong driving force for hole trapping and oxidation of iodide species. When in contact with a non-polar solvent, the migration of iodine species is further extended to expulsion of iodine from the perovskite film. Thus, the mobility of halides and their susceptibility to hole-induced oxidation play a crucial role in determining the long-term stability of metal halide perovskite solar cells. When Ruddlesden-Popper 2D mixed-halide perovskite films with spacer cations such as butylammonium are introduced into three-dimensional (3D) perovskite films, they can stabilize them against moisture-induced degradation at room temperature. While such passivation of 3D perovskites using 2D perovskites has been reported widely, the instability of the 2D/3D interface during long term solar cell operation can be problematic, especially at higher temperatures. The cation migration under light and heat can significantly alter the 2D/3D interface, thus affecting the solar cell performance. We have now probed the cation migration between 2D and 3D perovskites by physically pairing X PbI (X=butylammonium BA, oleylammonium OA, or phenethylammonium PEA) 2D film and (CH3)PbI3 3D film at different temperatures by recording changes in the absorption and emission spectra. Thus, suppression of halide ion migration as well as cation migration remains a key factor in achieving long term stability and improving efficiency of perovskite solar cells and light emitting devices.

Near‐Zero Segregation on Strongly Exciton Confined Mixed Halide Perovskites Quantum Dots via Octahedron Alloying Reconstruction Engineering

AbstractThe state‐of‐the‐art mixed‐halide perovskite (MHP) quantum dots (QDs) open up promising applications in photovoltaic and optoelectronic communities, yet are limited by huge halide segregation. In contrast to the previous A‐site alloy method, customizing other octahedral units for replacing the fundamental optoelectronic unit of [PbX6]4− (X = Cl, Br, or I), the so‐called B‐site alloying strategy, is expected to inhibit halide segregation fully. Here, a halide octahedron alloying reconstruction engineering is reported to fabricate MHP QDs with near‐zero halide segregation due to their strongly confined excitons. This unprecedented regime is obtained at a water–oil interfacial reaction system using amino‐silane ion exchange accelerator and transition metal hydroxy‐halides salts, introducing abundant [MX6]4− (M = Zn, Ni, Co, Mn, and Cu) octahedron block and finally fabricating transition metal‐alloyed MAPbX3 QDs. Photo‐induced excitons in strongly dielectric‐confined Zn‐alloyed perovskite QDs are hardly thermally dissociated and transferred, as featured by ultra‐high exciton binding energy (Eb), fast fluorescence lifetimes (τavg), and near 100% photoluminescence quantum yield (PLQY). The fabricated mixed‐halide MAPb1‐xZnxX3 QDs with reduced Pb content over 40% exhibit near‐zero halide segregation, marking the emergence of a practical solution to the detrimental segregation problem, which paves the wave for emerging solar cells and lighting display applications.

Dynamics of glassy state in MAPbBr3-xClx mixed lead halide perovskites

Mixed lead halide perovskites have shown remarkable performance in photovoltaic and optoelectronic applications. Pure hybrid halide perovskites undergo clear phase transitions, however, the phase transitions in mixed perovskites are less studied. We present a contrasting behavior of the phase transition dynamics of MAPbBr3-xClx (MA = CH3NH3+) mixed halide perovskites compared to the pure MAPbX3 (X = Cl, Br) counterparts, which typically exhibit order-disorder phase transitions through a series of distinct structural phases. We have employed several spectroscopic techniques including temperature-dependent PXRD, Raman, dielectric and Brillouin spectroscopy. The results demonstrate that the mixed halide perovskite MAPbBr1.5Cl1.5 does not undergo any structural phase transition typically observed in pure halide perovskites. We observed signatures of glassy behavior in mixed compositions of this system. In addition, we also explored the effects of replacing A-site cation on the phase transition behaviors. The results contribute to the understanding of phase transition mechanisms in perovskites and have implications for their stability and optoelectronic properties.

Unravelling Structural, Optical, and Band Alignment Properties of Mixed Pb-Sn Metal-Halide Quasi-2D Ruddlesden-Popper Perovskites.

Lead-tin (Pb-Sn) mixed-halide perovskites show potential for single-junction and tandem solar cells due to their adjustable band gaps, flexible composition, and superior environmental stability compared to three-dimensional (3D) perovskites. However, they have lower power conversion efficiencies. Understanding band alignment and charge carrier dynamics is essential for enhancing photovoltaic performance. In this view, herein we have prepared thin films of mixed Pb-Sn-based two dimensional (2D) Ruddlesden-Popper (RP) perovskites BA2FA(Pb1-xSnx)2I7 using a solution-based method. XRD study revealed the formation of orthorhombic phases for pristine (BA2FAPb2I7) and mixed Pb-Sn perovskite thin films. UV-vis analysis showed that different n = 2 and n = 3 phases are present in the pristine sample. In contrast, Pb-Sn-doped samples showed no signature of other phases with a prominent red-shift in the visible spectral region. Cyclic voltammetry showed peaks for electron transfers at the band edges. Additionally, electrochemical and optical band gap matching was observed, along with decreased peak intensity due to less reactant and altered electrolyte-perovskite interface stability. Density functional theory (DFT) calculations revealed that the reduced band gap is due to the alteration of electrostatic interactions and charge distribution within the lattice upon Sn substitution. Low-temperature PL analysis provided insights into charge carrier dynamics with Sn substitution and suggested the suppression of higher n phases and self-trapped excitons/carriers in mixed Pb-Sn quasi-2D RP perovskite thin films. This study sheds light on the electron transfer phenomena between TiO2 and SnO2 layers by estimating band offsets from valence band maximum (VBM) and conduction band minimum (CBM), which is crucial for future applications in fabricating stable and efficient 2D-Pb-Sn mixed perovskites for optoelectronic applications.

A DFT approach on the investigations of the structural and optoelectronic properties of lead-free and Ge-based mixed halide perovskites RbGeBr2Cl and RbGeI2Cl

A DFT approach on the investigations of the structural and optoelectronic properties of lead-free and Ge-based mixed halide perovskites RbGeBr2Cl and RbGeI2Cl

Saturable absorption properties of mixed lead-tin halide perovskites and their application in near-infrared ultrafast lasers

Mixed lead–tin halide perovskites, as highly sensitive materials in the near-infrared region, hold significant potential for optoelectronic device applications. Here, mixed lead–tin halide perovskite saturable absorbers (SAs) have been developed by coupling with the side-polished surfaces of the single-mode fibers and excellent saturable absorption effects of the mixed lead–tin halide perovskite SAs have been demonstrated in the near-infrared region. By constructing the in-gap site assisted carrier transfer mode, the saturation absorption process of the mixed lead–tin halide perovskite SAs can be well explained, in which defects as in-gap sites can help the photon-generated carriers transfer into the conduction band and promote the Pauli-blocking-induced absorption bleaching in the SA. Moreover, ytterbium-doped fiber lasers based on perovskite SAs have been fabricated, and mode-locked operations at 1040 nm are achieved using the mixed lead–tin halide perovskite SA, generating ultra-short pulses with a pulse width of 683 fs, 3 dB bandwidth of 4.88 nm, signal-to-noise ratio exceeding 49.74 dB, and a repetition rate of 3.74 MHz. Our findings demonstrate that the mixed lead–tin halide perovskite SAs have excellent optical modulation capability and promising applications in the field of ultrafast photonics.

Sustainable Mixed-Halide Perovskite Resistive Switching Memories Using Self-Assembled Monolayers as the Bottom Contact.

The complex ionic-electronic conduction in mixed halide perovskites enables their use beyond von Neumann architectures implemented in resistive switching memory devices. Although device fabrication based on perovskite compounds involves solution-processing at low temperatures, reducing further fabrication costs by eliminating expensive materials can improve their compatibility with upscalable deposition techniques. Notably, the substrate on which the perovskite active layer is developed has been reported to severely affect its quality and thus the overall device performance. Hereby, we demonstrate the sustainable manufacturing of memristive perovskite solar cells by replacing the expensive poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) that serves as a hole transporting layer (HTL) with a self-assembled monolayer (SAM), namely [2-(3,6-dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic acid (MeO-2PACz). Multiple sequential memristive current-voltage characteristics of single devices are reported, and average data of multiple reference and targeted devices are compared. Resistive switching memory devices based on SAM exhibit improved performance having reduced average SET voltage values and narrower statistical variation compared to reference devices with PTAA. It is shown that both PTAA and SAM based devices exhibit high ON/OFF ratio of about 103 operating at low switching electric fields. Replacing an expensive polymer-based HTL with this approach reduces fabrication costs compared to PTAA.

Highly efficient blue light-emitting diodes based on mixed-halide perovskites with reduced chlorine defects.

Perovskite light-emitting diodes (PeLEDs) provide excellent opportunities for low-cost, color-saturated, and large-area displays. However, the performance of blue PeLEDs lags far behind that of their green and red counterparts. Here, we show that the external quantum efficiencies (EQEs) of blue PeLEDs scale linearly with the photoluminescence quantum yields (PL QYs) of CsPb(BrxCl1-x)3 nanocrystals emitting at 460 to 480 nm. The recombination efficiency of carriers is highly sensitive to the chlorine content and the related deep-level defects in nanocrystals, causing notable EQE drops even with minor increases in chlorine defects. Minor adjustments of chlorine content through rubidium compensation on the A-site effectively suppress the formation of nonradiative defects, improving PL QYs while retaining desirable bandgaps for blue-emitting nanocrystals. Our PeLEDs with record-high efficiencies span the blue spectrum, achieving peak EQEs of 12.0% (460 nm), 16.7% (465 nm), 21.3% (470 nm), 24.3% (475 nm), and 26.4% (480 nm). This work exemplifies chlorine-defect control as a key design principle for high-efficiency blue PeLEDs.

Exploration HTL-Free all inorganic mixed halide perovskite solar cells: effects of 4-ADPA passivation

The incredible PV performance of thin-film perovskite solar cells has garnered the attention of researchers. Mixed halide perovskite outweighs pure halide perovskite in its ability to optimize PV performance while performing material composition engineering. All inorganic mixed halide (AIMH) perovskite CsPbI2Br has shown stable performance against thermal variations. This study mainly highlights the performance of HTL (Hole transport layer) free, passivated solar cell structure with utilization of the SCAPS-1D simulator. The inclusion of passivation layer 4-ADPA(4-aminodiphenylamine) between active layer CsPbI2Br and the end electrode mitigates the occurrence of charge carrier recombination. The thickness of passivation layer 4-ADPA is optimized for the range 100 nm–1000 nm, and 100 nm is decided as the optimum width based on the evaluated PV performance of SnO2/CsPbI2Br/4-ADPA/anode. 4-ADPA layer with an optimum thickness of 100 nm, is embedded with a CsPbI2Br layer, and the performance of solar cell has been investigated under the collective impact of BDD (bulk defect density)/thickness of CsPbI2Br for the range (1012 cm−3 to 1018 cm−3)/(50 nm to 500 nm) respectively. Further, this study investigated the capacitance–voltage (C-V), Mott—Schottky (1/C2), and Nyquist plot (C-F) performance of solar cells under the influence of only BDD for two cell configurations (corresponding to maximum and minimum delivered PCE i.e., thickness/BDD is 200 nm/1012 cm−3 and 500 nm/1018 cm−3 respectively). The highest 13.27% of PCE is extracted from HTL-free, 4-ADPA passivated all inorganic PSC, at 200 nm/1012 cm−3 of thickness/BDD respectively. This technique encourages researchers to explore more cost-effective, HTL-free passivated solar cell structures.

Spectrally Stable and Bright Red Perovskite Light-Emitting Diodes.

Mixing iodide and bromide in three-dimensional metal-halide perovskites is a facile strategy for achieving red light-emitting diodes (LEDs). However, these devices often face challenges such as instability in electroluminescence spectra and low brightness due to phase segregation in mixed-halide perovskites. Here, we demonstrate spectrally stable and bright red perovskite LEDs by substituting some of the halide ions with pseudohalogen thiocyanate ions (SCN-). We find that SCN- can occupy halogen vacancies, thereby releasing microstrain and passivating defects in the perovskite crystals. This leads to the suppression of mixed-halide phase segregation under electrical bias. As a result, the red perovskite LEDs exhibit a high brightness of >35 000 cd m-2 with stable Commission Internationale de l'Eclairage (CIE) coordinates of (0.713, 0.282). This brightness surpasses that of the best-performing red perovskite LEDs, showing great promise for advancing perovskite LEDs in display and lighting applications.

Theoretical study of lead-free mixed-valence mixed-halide Au-based perovskites for optoelectronics

Inorganic mixed-valence Au-based perovskites have received considerable attention due to their nontoxic elements, good stability and superior properties. Hence it is of significant interest to explore more novel Au-based perovskite materials for solar cell applications. This study presents a detailed theoretical exploration on the structural features, thermodynamic and mechanical stability, optoelectronic characteristics, and photovoltaic performance of Cs2AuIAuIIICl6-xBrx, Cs2AuIAuIIICl6-xIx, and Cs2AuIAuIIIBr6-xIx (x = 2, 4) in comparison with that of Cs2AuIAuIIIX6 (X = Cl, Br, I). Through the comprehensive evaluation of thermodynamic and mechanical stability, Cs2AuIAuIIIX2Y4 (X2Y4Cl2Br4, Cl2I4, and Br2I4) is identified to be stable. The impact of anion substitution on the electronic characteristics of these mixed-halide Au-based perovskites is thoroughly disclosed. It is observed from band structure calculations that Cs2AuIAuIIIX4Y2 (X4Y2Cl4Br2, Cl4I2, and Br4I2) exhibits a lower direct-gap within 0.7–1.0 eV, while Cs2AuIAuIIIX2Y4 (X2Y4Cl2Br4, Cl2I4, and Br2I4) possesses an indirect-gap with ∼1.1 eV. The nonlinear band gap variation is disclosed and reasonably explained. Furthermore, Cs2AuIAuIIIX2Y4 displays strong dipole-allowed visible-light absorption. In addition, the simulated efficiency of Cs2AuIAuIIIX2Y4 is within ∼28–30 %, which is comparable to those of GaAs and CH3NH3PbI3. This theoretical exploration is helpful for developing more novel inorganic Au-based perovskites with desirable photovoltaic performance.

Positive Effects of Guanidinium Salt Post-Treatment on Multi-Cation Mixed Halide Perovskite Solar Cells.

As one of the most promising photovoltaic technologies, perovskite solar cells (PSCs) exhibit high absorption coefficients, tunable bandgaps, large carrier mobilities, and versatile fabrication techniques. Nevertheless, the commercialization of the technology is hindered by poor material stability, short device lifetimes and the scalability of fabrication techniques. To address these technological drawbacks, various strategies have been explored, with one particularly promising approach involving the formation of a low-dimensional layer on the surface of the three-dimensional perovskite film. In this work, we demonstrate the use of guanidinium tetrafluoroborate, CH6BF4N3, (GATFB) as a post-treatment step to enhance the performance of PSCs. Compared with the control sample, the application of GATFB improves the film surface topology, reduces surface defects, suppresses non-radiative recombination, and optimizes band alignment within the device. These positive effects reduce recombination losses and enhance charge transport in the device, resulting in PSCs with an open-circuit voltage (VOC) of 1.18 V and a power conversion efficiency (PCE) of 19.7%. The results obtained in this work exhibit the potential of integrating low-dimensional structures in PSCs as an effective approach to enhance the overall device performance, providing useful information for further advancement in this rapidly evolving field of photovoltaic technology.