Core/Shell Perovskite Nanocrystals: Synthesis of Highly Efficient and Environmentally Stable FAPbBr3/CsPbBr3 for LED Applications

Lead halide perovskite nanocrystals (PeNCs) are promising materials for applications in optoelectronics. However, their environmental instability remains to be addressed to enable their advancement into industry. Here the development of a novel synthesis method is reported for monodispersed PeNCs coated with all inorganic shell of cesium lead bromide (CsPbBr₃) grown epitaxially on the surface of formamidinium lead bromide (FAPbBr₃) NCs. The formed FAPbBr₃/CsPbBr₃ NCs have photoluminescence in the visible range 460–560 nm with narrow emission linewidth (20 nm) and high optical quantum yield, photoluminescence quantum yield (PLQY) up to 93%. The core/shell perovskites have enhanced optical stability under ambient conditions (70 d) and under ultraviolet radiation (50 h). The enhanced properties are attributed to overgrowth of FAPbBr₃ with all‐inorganic CsPbBr₃ shell, which acts as a protective layer and enables effective passivation of the surface defects. The use of these green‐emitting core/shell FAPbBr₃/CsPbBr₃ NCs is demonstrated in light‐emitting diodes (LEDs) and significant enhancement of their performance is achieved compared to core only FAPbBr₃‐LEDs. The maximum current efficiency observed in core/shell NC LED is 19.75 cd A^‐1 and the external quantum efficiency of 8.1%, which are approximately four times and approximately eight times higher, respectively, compared to core‐only devices.     

Photovoltaic and Amplified Spontaneous Emission Studies of High‐Quality Formamidinium Lead Bromide Perovskite Films

This study demonstrates the formation of extremely smooth and uniform formamidinium lead bromide (CH(NH₂)₂PbBr₃ = FAPbBr₃) films using an optimum mixture of dimethyl sulfoxide and N,N‐dimethylformamide solvents. Surface morphology and phase purity of the FAPbBr₃ films are thoroughly examined by field emission scanning electron microscopy and powder X‐ray diffraction, respectively. To unravel the photophysical properties of these films, systematic investigation based on time‐integrated and time‐dependent photoluminescence studies are carried out which, respectively, bring out relatively lower nonradiative recombination rates and long lasting photogenerated charge carriers in FAPbBr₃ perovskite films. The devices based on FTO/TiO₂/FAPbBr₃/spiro‐OMeTAD/Au show highly reproducible open‐circuit voltage (V_oc) of 1.42 V, a record for FAPbBr₃‐based perovskite solar cells. V_oc as a function of illumination intensity indicates that the contacts are very selective and higher V_oc values are expected to be achieved when the quality of the FAPbBr₃ film is further improved. Overall, the devices based on these films reveal appreciable power conversion efficiency of 7% under standard illumination conditions with negligible hysteresis. Finally, the amplified spontaneous emission (ASE) behavior explored in a cavity‐free configuration for FAPbBr₃ perovskite films shows a sharp ASE threshold at a fluence of 190 μJ cm^?2 with high quantum efficiency further confirming the high quality of the films.     

24.64%-Efficiency MA-Free Perovskite Solar Cell with Voc of 1.19 V Enabled by a Hinge-Type Fluorine-Rich Complex

High density of defects at interface severely affects the performance of perovskite solar cells (PSCs). Herein, cobalt (II) hexafluoro-2,4-pentanedionat (CoFAc), a hinge-type fluorine-rich complex, is introduced onto the surface of formamidinium cesium lead iodide (FACsPbI₃) film to address the issues of perovskite/Spiro-OMeTAD interface. The existence of CoFAc passivates both organic cation and halide anion vacancies by establishing powerful hydrogen bonds with HC(NH₂)₂⁺ (FA⁺) and strong ionic bonds with Pb²⁺ in perovskite films. In addition, CoFAc serves as a connecting link to enhance interfacial hole-transport kinetics via interacting with Spiro-OMeTAD. Consequently, FACsPbI₃ PSCs with CoFAc modification display a champion power conversion efficiency (PCE) of 24.64% with a charming open-circuit voltage (V_OC) of 1.191 V, which is the record V_OC among all the reported organic-inorganic hybrid PSCs with TiO₂ as electron transport layer. Furthermore, CoFAc-modified devices exhibit an outstanding long-term stability, which can maintain 95% of their initial PCEs after exposure to ambient atmosphere for 1500 h without any encapsulation.     

Surface Regulation through Dipolar Molecule Boosting the Efficiency of Mixed 2D/3D Perovskite Solar Cell to 24%

Mixed 2D/3D perovskite solar cells (PSCs) show promising performances in efficiency and long-term stability. The functional groups terminated on a large organic molecule used to construct 2D capping layer play a key role in the chemical interaction mechanism and thus influence the device performance. In this study, 4-(trifluoromethyl) benzamidine hydrochloride (TFPhFACl) is adopted to construct 2D capping layer atop 3D perovskite. It is found that there are two mechanisms synergistically contributing to the increase of efficiency: 1) The TFPhFA⁺ cations form a dipole layer promoting the interfacial charge transport. 2) The suppressed nonradiative recombination of perovskite through the coordination of TFPhFA⁺ cations with Pb–I octahedron, as well as the recrystallization of 3D perovskite induced by Cl^- ions. As a result, the PSC delivers an efficiency of 24.0% with improved open-circuit voltage (V_OC) of 1.16 V, short-circuit current density (J_SC) of 25.42 mA cm^-2, and fill factor of 81.26%. The device shows no decrease in efficiency after 1500 h stored in the air indicating the good stability. The utilization of TFPhFACl not only provides a facile way to optimize the interfacial problems, but also gives a new perspective for rational design of large spacer molecule for constructing efficient 2D/3D PSCs.     

Improving the Performance of Perovskite Solar Cells via a Novel Additive of N,1-Fluoroformamidinium Iodide with Electron-Withdrawing Fluorine Group

Additives are widely adopted for efficient perovskite solar cells (PSCs), and proper additive design contributes a lot to PSCs’ various breakthroughs. Herein, a novel additive of N,1-fluoroformamidinium iodide (F-FAI), whose cation replaces one amino group in guanidinium (GA⁺) with electron-withdrawing fluorine group, is synthesized and applied as the additive for PSCs. The electron-withdrawing effect of fluorine promotes the molecular polarity of N,1-fluoroformamidine (F-FA), enhancing the interaction of N,1-fluoroformamidinium (F-FA⁺) with MAPbI₃. Compared with the nonpolar GA⁺, F-FA⁺ improves the crystallinity, passivates the defect, and downshifts the Fermi level of MAPbI₃ more significantly. The charge transfer and built-in field in printable triple mesoscopic PSCs are therefore enhanced. Moreover, charge transport in MAPbI₃ is also promoted by F-FAI. With these benefits, a power conversion efficiency of 17.01% for printable triple mesoscopic PSCs with improved open-circuit voltage and fill factor is obtained with the addition of F-FAI, superior to the efficiency of 15.24% for those devices with guanidinium iodide additives.     

Flexible Piezoelectric Nanocomposite Generators Based on Formamidinium Lead Halide Perovskite Nanoparticles

Organic–inorganic lead halide perovskite materials have recently attracted much attention in the field of optoelectronic devices. Here, a hybrid piezoelectric nanogenerator based on a composite of piezoelectric formamidinium lead halide perovskite (FAPbBr₃) nanoparticles and polydimethylsiloxane polymer is fabricated. Piezoresponse force spectroscopy measurements reveal that the FAPbBr₃ nanoparticles contain well‐developed ferroelectric properties with high piezoelectric charge coefficient (d₃₃) of 25 pmV⁻¹. The flexible device exhibits high performance with a maximum recordable piezoelectric output voltage of 8.5 V and current density of 3.8 μA cm⁻² under periodically vertical compression and release operations. The alternating energy generated from nanogenerators can be used to charge a capacitor and light up a red light‐emitting diode through a bridge rectifier. This result innovatively expands the feasibility of organic–inorganic lead halide perovskite materials for application in a wide variety of high‐performance energy harvesting devices.     

Room‐Temperature Ion‐Exchange‐Mediated Self‐Assembly toward Formamidinium Perovskite Nanoplates with Finely Tunable,Ultrapure Green Emissions for Achieving Rec. 2020 Displays

Delicate engineering of chromaticity is required to faithfully reproduce colors in a backlit display, this is extremely difficult for green downconverters because the human eye is highly sensitive to green colors. The central challenge is to achieve finely tunable green emissions in the narrow range of 525–535 nm while keeping the full width at half maximum (FWHM) <25 nm at the same time. Here, a room‐temperature ion‐exchange‐mediated self‐assembly strategy for preparing FAPbBr₃ (FA = CH(NH₂)₂⁺) nanoplates (NPs) to fulfill this goal is introduced. 2D layered OA₂PbBr₄ (OA is octadecylamine) NPs are first synthesized by spontaneous reprecipitation, and are then transformed into FAPbBr₃ NPs through a OA⁺‐to‐FA⁺ exchange induced self‐assembly of HP monolayers. A c‐axis contraction in this process makes a relative large thickness variation in OA₂PbBr₄ NPs, which can be realized by simply varying the precursor concentration, only result in a small thickness change in subsequent FAPbBr₃ NPs, thereby enabling finely tunable emissions in the range of 525–535 nm along with FWHM <25 nm and a quantum yield up to 85%. As a downconverter, the FAPbBr₃ NPs realize an ultrapure green backlight that covers ≈95% Rec. 2020 standard in the CIE 1931 color space.     

Spacer Cation Tuning Enables Vertically Oriented and Graded Quasi-2D Perovskites for Efficient Solar Cells

Halide substitution in phenethylammonium spacer cations (X-PEA⁺, X  = F, Cl, Br) is a facile strategy to improve the performance of PEA based perovskite solar cells (PSCs). However, the power conversion efficiency (PCE) of X-PEA based quasi-2D (Q-2D) PSCs is still unsatisfactory and the underlying mechanisms are in debate. Here, the in-depth study on the impact of halide substitution on the crystal orientation and multi-phase distribution in PEA based perovskite films are reported. The halide substitution eliminates n  =  1 2D perovskite and thus leads to the perpendicular crystal orientation. Furthermore, nucleation competition exists between small-n and large-n phases in PEA and X-PEA based perovskites. This gives rise to the orderly distribution of different n-phases in the PEA and F-PEA based films, and random distribution in Cl-PEA and Br-PEA based films. As a result, (F-PEA)₂MA₃Pb₄I₁₂ (MA = CH₃NH₃⁺, n = 4) based PSCs achieve a PCE of 18.10%, significantly higher than those of PEA (12.23%), Cl-PEA (7.93%) and Br-PEA (6.08%) based PSCs. Moreover, the F-PEA based devices exhibit remarkably improved stability compared to their 3D counterparts.     

Intraband Cooling in All‐Inorganic and Hybrid Organic–Inorganic Perovskite Nanocrystals

Intraband relaxation in all‐inorganic cesium lead tribromide (CsPbBr₃) and hybrid organic–inorganic formamidinium lead tribromide (FAPbBr₃) nanocrystals is experimentally investigated for a range of particle sizes, excitation energies, sample temperatures, and excitation fluences. Hot carriers in CsPbBr₃ nanocrystals consistently exhibit slower cooling than FAPbBr₃ nanocrystals in the single electron–hole pair per nanocrystal regime. In both compositions, long‐lived hot carriers (>3 ps) are only observed at excitation densities corresponding to production of multiple electron–hole pairs per nanocrystal—and concomitant Auger recombination. These presented results are distinct from previous reports in bulk hybrid perovskite materials that convey persistent hot carriers at low excitation fluences. Time‐resolved photoluminescence confirms the rapid cooling of carriers in the low‐fluence (single electron–hole pair per nanocrystal) regime. Intraband relaxation processes, as a function of excitation energy, size, and temperature are broadly consistent with other nanocrystalline semiconductor materials.     

Chemical Reduction of Iodine Impurities and Defects with Potassium Formate for Efficient and Stable Perovskite Solar Cells

The performance of perovskite solar cells (PSCs) is negatively affected by iodine (I₂) impurities generated from the oxidation of iodide ions in the perovskite precursor powder, solution, and perovskite films. In this study, the use of potassium formate (HCOOK) as a reductant to minimize the presence of detrimental I₂ impurities is presented. It is demonstrated that HCOOK can effectively reduce I₂ back to I⁻ in the precursor solution as well as in the devices under external conditions. Furthermore, the introduced formate anion (HCOO⁻) and alkali metal cation (K⁺) can reduce the defect density within the perovskite film by modulating perovskite growth and passivating electronic defects, significantly prolonging the carrier lifetime and reducing the J–V hysteresis. Consequently, the maximum efficiency of the HCOOK-doped planar n–i–p PSCs reaches 23.8%. After 1000 h of operation at maximum power point tracking under continuous 1 sun illumination, the corresponding encapsulated devices retain 94% of their initial efficiency.     

Bidirectional Targeted Therapy Enables Efficient,Stable, and Eco-Friendly Perovskite Solar Cells

Perovskite solar cells (PSCs) have witnessed rapid development toward commercialization based on their superior efficiency except for some remained misgivings about their poor stability primarily originating from interfacial problems. Robust back interface for neutralization of crystal defects, depression of dopant lithium ions (Li⁺) diffusion, and even inhibition of toxic lead (Pb) leakage is highly desirable; however, it remains a great challenge. Herein, a cost-effective interfacial therapy approach is developed to simultaneously alleviate the obstacles aforementioned. A small molecule, 1,4-dithiane with unique chair structure, is adapted to interact with under-coordinated Pb²⁺ on perovskite surface and Li⁺ from hole transport layer, neutralizing interfacial defects and suppressing Li⁺ diffusion. Besides, the presence of 1,4-dithiane can efficiently modulate interfacial energetics, enhance hydrophobicity of PSCs, and anchor Pb atoms via S Pb bond. Consequently, the target devices perform better than control devices when exposed to light-soaking, moisture, and thermal stress owing to the synergistic suppression of trap-state density, ions migration, and moisture permeation. The optimized target device delivers a champion efficiency of 23.27% with mitigated Pb leakage. This study demonstrates a promising functionalized modification strategy for constructing efficient, stable, and eco-friendly PSCs.     

Introduction of Hydrophobic Ammonium Salts with Halogen Functional Groups for High‐Efficiency and Stable 2D/3D Perovskite Solar Cells

2D perovskites have attracted extensive attention due to their excellent stability compared with 3D perovskites. However, the intrinsic hydrophilicity of introduced alkylammonium salts effects the humidity stability of 2D/3D perovskites. Devices based on longer chain alkylammonium salts show improvement in hydrophobicity but lower efficiency due to the poorer charge transport among various layers. To solve this issue, two hydrophobic short‐chain alkylammonium salts with halogen functional groups (2‐chloroethylamine, CEA⁺ and 2‐bromoethylamine, BEA⁺) are introduced into (Cs_0.1FA_0.9)Pb(I_0.9Br_0.1)₃ 3D perovskites to form 2D/3D perovskite structure, which achieve high‐quality perovskite films with better crystallization and morphology. The optimal 2D/3D perovskite solar cells (PSCs) with 5% CEA⁺ display a power conversion efficiency (PCE) as high as 20.08% under 1 sun irradiation. Because of the notable hydrophobicity of alkylammonium cations with halogen functional groups and the formed 2D/3D perovskite structure, the optimal PSCs exhibit superior moisture resistance and retain 92% initial PCE after aging at 50 ± 5% relative humidity for 2400 h. This work opens up a new direction for the design of new‐type 2D/3D PSCs with improved performance by employing proper alkylammonium salts with different functional groups.     

Aqueous solution-processed MoO3 as an effective interfacial layer in polymer/fullerene based organic solar cells

The authors demonstrate an effective anode interfacial layer based on aqueous solution-processed MoO₃ (sMoO₃) in poly (3-hexylthiophene) (P3HT) and indene-C60 bisadduct (ICBA) based bulk-heterojunction organic solar cells (PSCs). Various sMoO₃ concentration (0.03–0.25 wt%) was obtained by dissolving MoO₃ powder into deionized water directly with weak solubility. The characteristics of sMoO₃ films evaluated by atomic force microscope (AFM) and scanning electron microscope (SEM) suggest that the sMoO₃ films continuously cover the entire indium tin oxide (ITO) surface. The sMoO₃ based PSCs exhibit comparable power conversion efficiency with poly (3,4-ethylenedioxythiophene)–polystyrenesulfonic acid (PEDOT:PSS) based devices. However, even more importantly, the stability of sMoO₃ based devices have been greatly improved in air under continual light-illumination at 52 mW/cm². Further evaluations on Mo valence states and work function of sMoO₃ films by X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) demonstrate that the aqueous solution-processed MoO₃ could act as an better anode interfacial layer than the conventional PEDOT:PSS.     

Facile method for the preparation of high-performance photodetectors with a GQDs/perovskite bilayer heterostructure

A high-performance nitrogen doped graphene quantum dots (GQDs)/all-inorganic (CsPbBr₃) perovskite nanocrystals (NCs) heterostructure photodetector was fabricated on a quartz substrate, using the low cost spin coating technique followed by hot plate annealing. The GQDs/CsPbBr₃ NCs heterostructure photodetector exhibits a high overall performance with a photoresponsivity of 0.24 AW⁻¹, on/off ratio of 7.2 × 10⁴, and specific detectivity of up to 2.5 × 10¹² Jones. The on/off ratio of the hybrid device was improved by almost ten orders of magnitude, and the photoresponsivity was enhanced almost three times compared to the single layer perovskite NCs photodetector. The performance enhancement of the hybrid device was due to its highly efficient carrier separation at the GQDs/CsPbBr₃ NCs interface. This results from the coupling of the GQDs layer, which efficiently extracts and transports the photogenerated carriers, with the CsPbBr₃ NCs layer, which has a large absorption coefficient and high quantum efficiency. The interfacial charge transfer from the CsPbBr₃ NCs to the GQDs layer was demonstrated by the quenching in the photoluminescence (PL) spectra, and the fast-average decay time in the time-resolved photoluminescence (Trpl) spectra of the hybrid photodetector. Moreover, the performance-enhancement mechanism of the hybrid GQDs/CsPbBr₃ photodetector was elucidated by analyzing the band alignment of the GQDs and CsPbBr₃ under laser illumination.     

Piezoelectric Nanogenerator Based on In Situ Growth All-Inorganic CsPbBr3 Perovskite Nanocrystals in PVDF Fibers with Long-Term Stability

Inorganic lead halide perovskite has become an emerging material for modern photoelectric and electronic nanodevices due to its excellent optical and electronic properties. In view of its huge dielectric and electrical properties, inorganic CsPbBr₃ perovskite is introduced into the piezoelectric nanogenerator (PENG). Based on one-step electrospinning of solutions containing CsPbBr₃ precursors and polyvinylidene difluoride (PVDF), in situ growth of CsPbBr₃ nanocrystals in PVDF fibers (CsPbBr₃@PVDF composite fibers) with highly uniform size and spatial distribution are synthesized. The CsPbBr₃@PVDF composite fibers based PENG reveals an open-circuit voltage (V_oc) of 103 V and a density of short-circuit current (I_sc) of 170  µ A cm⁻², where the V_oc is comparable to the state-of-the-art hybrid composite piezoelectric nanogenerators (PENGs) and the density of I_sc is 4.86 times higher than that of lead halide perovskites counterpart ever reported. Moreover, CsPbBr₃@PVDF composite fibers based PENG exhibits fundamentally improved thermal/water/acid–base stabilities. This study suggests that the CsPbBr₃@PVDF composite fiber is a good candidate for fabricating high-performance PENGs, promising application potentials in mechanical energy harvesting and motion sensing technologies.     

Origin of Open‐Circuit Voltage Enhancements in Planar Perovskite Solar Cells Induced by Addition of Bulky Organic Cations

The origin of performance enhancements in p‐i‐n perovskite solar cells (PSCs) when incorporating low concentrations of the bulky cation 1‐naphthylmethylamine (NMA) are discussed. A 0.25 vol % addition of NMA increases the open circuit voltage (V_oc) of methylammonium lead iodide (MAPbI₃) PSCs from 1.06 to 1.16 V and their power conversion efficiency (PCE) from 18.7% to 20.1%. X‐ray photoelectron spectroscopy and low energy ion scattering data show NMA is located at grain surfaces, not the bulk. Scanning electron microscopy shows combining NMA addition with solvent assisted annealing creates large grains that span the active layer. Steady state and transient photoluminescence data show NMA suppresses non‐radiative recombination resulting from charge trapping, consistent with passivation of grain surfaces. Increasing the NMA concentration reduces device short‐circuit current density and PCE, also suppressing photoluminescence quenching at charge transport layers. Both V_oc and PCE enhancements are observed when bulky cations (phenyl(ethyl/methyl)ammonium) are incorporated, but not smaller cations (Cs/MA)—indicating size is a key parameter. Finally, it demonstrates that NMA also enhances mixed iodide/bromide wide bandgap PSCs (V_oc of 1.22 V with a 1.68 eV bandgap). The results demonstrate a facile approach to maximizing V_oc and provide insights into morphological control and charge carrier dynamics induced by bulky cations in PSCs.     

Fluorinated Black Phosphorene Nanosheets with Robust Ambient Stability for Efficient and Stable Perovskite Solar Cells

Extraordinary electronic and photonic features (e.g., tunable direct bandgap, high ambipolar carrier mobility) render few-layer black phosphorus (BP) nanosheets/quantum dots an important optoelectronic material. However, most of the BP applied in metal halide perovskite solar cells (PSCs) are produced by sonication-assisted liquid exfoliation, which inevitably brings inferior electronic properties, thus leading to limited beneficial effects. Furthermore, this study uncovers that the intrinsic instability of BP nanosheets sandwiched between (CsFAMA)Pb(BrI)₃ perovskite and spiro-OMeTAD has a deleterious effect on the performance stabilization of PSCs. To address the above constraints, a feasible strategy herein is developed by introducing high-quality fluorinated BP (F-BP) nanosheets synthesized by one-step electrochemical delamination. In addition to P-Pb coordination, there is a strong hydrogen bond between F^? and MA⁺/FA⁺ as well as an ionic bond between F^? and Pb²⁺ for the perovskite/F-BP interface, thus leading to fewer interfacial traps than perovskite/BP, which is responsible for the highest power conversion efficiency (22.06%) of F-BP devices. More importantly, F-BP devices exhibit significantly improved humidity and shelf-life stabilities due to the excellent ambient stability of F-BP, resulting from the antioxidation and antihydration behavior of fluorine adatoms. Overall, the findings provide a promising strategy to simultaneously enhance the photovoltaic performance and long-term stability of BP-based PSCs.     

Defect Passivation via the Incorporation of Tetrapropylammonium Cation Leading to Stability Enhancement in Lead Halide Perovskite

Improving the performances of photovoltaic (PV) devices by suppressing nonradiative energy losses through surface defect passivation and enhancing the stability to the level of standard PV represents one critical challenge for perovskite solar cells. Here, reported are the advantages of introducing a tetrapropylammonium (TPA⁺) cation that combines two key functionalities, namely surface passivation of CH₃NH₃PbI₃ nanocrystals through strong ionic interaction with the surface and bulk passivation via formation of a type I heterostructure that acts as a recombination barrier. As a result, nonencapsulated perovskite devices with only 2 mol% of TPA⁺ achieve power conversion efficiencies over 18.5% with higher V_OC under air mass 1.5G conditions. The devices fabricated retain more than 85% of their initial performances for over 1500 h under ambient conditions (55% RH ± 5%). Furthermore, devices with TPA⁺ also exhibit excellent operational stability by retaining over 85% of the initial performance after 250 h at maximum power point under 1 sun illumination. The effect of incorporation of TPA⁺ on the structural and optoelectronic properties is studied by X‐ray diffraction, ultraviolet–visible absorption spectroscopy, ultraviolet photon–electron spectroscopy, time‐resolved photoluminescence, and scanning electron microscopy imaging. Atomic‐level passivation upon addition of TPA⁺ is elucidated employing 2D solid‐state NMR spectroscopy.     

Advanced Characterization and Optimization of NiOx:Cu-SAM Hole-Transporting Bi-Layer for 23.4% Efficient Monolithic Cu(In,Ga)Se2-Perovskite Tandem Solar Cells

The performance of five hole-transporting layers (HTLs) is investigated in both single-junction perovskite and Cu(In, Ga)Se₂ (CIGSe)-perovskite tandem solar cells: nickel oxide (NiO_x,), copper-doped nickel oxide (NiO_x:Cu), NiO_x+SAM, NiO_x:Cu+SAM, and SAM, where SAM is the [2-(3,-6Dimethoxy-9H-carbazol-9yl)ethyl]phosphonic acid (MeO-2PACz) self-assembled monolayer. The performance of the devices is correlated to the charge-carrier dynamics at the HTL/perovskite interface and the limiting factors of these HTLs are analyzed by performing time-resolved and absolute photoluminescence ((Tr)PL), transient surface photovoltage (tr-SPV), and X-ray/UV photoemission spectroscopy (XPS/UPS) measurements on indium tin oxide (ITO)/HTL/perovskite and CIGSe/HTL/perovskite stacks. A high quasi-Fermi level splitting to open-circuit (QFLS-V_oc) deficit is detected for the NiO_x-based devices, attributed to electron trapping and poor hole extraction at the NiO_x-perovskite interface and a low carrier effective lifetime in the bulk of the perovskite. Simultaneously, doping the NiO_x with 2% Cu and passivating its surface with MeO-2PACz suppresses the electron trapping, enhances the holes extraction, reduces the non-radiative interfacial recombination, and improves the band alignment. Due to this superior interfacial charge-carrier dynamics, NiO_x:Cu+SAM is found to be the most suitable HTL for the monolithic CIGSe-perovskite tandem devices, enabling a power-conversion efficiency (PCE) of 23.4%, V_oc of 1.72V, and a fill factor (FF) of 71%, while the remaining four HTLs suffer from prominent V_oc and FF losses.     

Rubidium Fluoride Modified SnO2 for Planar n-i-p Perovskite Solar Cells

Regulating the electron transport layer (ETL) has been an effective way to promote the power conversion efficiency (PCE) of perovskite solar cells (PSCs) as well as suppress their hysteresis. Herein, the SnO₂ ETL using a cost-effective modification material rubidium fluoride (RbF) is modified in two methods: 1) adding RbF into SnO₂ colloidal dispersion, F and Sn have a strong interaction, confirmed via X-ray photoelectron spectra and density functional theory results, contributing to the improved electron mobility of SnO₂; 2) depositing RbF at the SnO₂/perovskite interface, Rb⁺ cations actively escape into the interstitial sites of the perovskite lattice to inhibit ions migration and reduce non-radiative recombination, which dedicates to the improved open-circuit voltage (V_oc) for the PSCs with suppressed hysteresis. In addition, double-sided passivated PSCs, RbF on the SnO₂ surface, and p-methoxyphenethylammonium iodide on the perovskite surface, produces an outstanding PCE of 23.38% with a V_oc of 1.213 V, corresponding to an extremely small V_oc deficit of 0.347 V.