CsPbI2Br Perovskite Films Research Articles

Effects of 3-Bromo-N-methylbenzylamine modification on CsPbI2Br perovskite films and perovskite solar cells

In this work, 3-Bromo-N-methylbenzylamine (3-B-N-MB) was designed to modify CsPbI2Br/hole transport layer interface to reduce the interfacial non-radiative recombination loss of all-inorganic CsPbI2Br perovskite solar cells (PSCs). The effects of 3-B-N-MB modification on the morphology, structure, optical absorption, defect concentration, carrier lifetime, energy level, hydrophobicity of CsPbI2Br perovskite film and device performance, and carrier dynamics, as well as their mechanisms were systematically studied. The results show that the lone pair electrons in the N atom of N-H group in strongly alkaline 3-B-N-MB is more conducive to coordinate with uncoordinated Pb2+/Cs+ in CsPbI2Br, meanwhile the H atom of N-H group in 3-B-N-MB can react with I−/Br− in CsPbI2Br through hydrogen bonding, passivating interface defects to increase grain size and enhance the crystallinity and density of CsPbI2Br films, optimizing interface energy level matching to promote carrier transport, thus suppressing interfacial non-radiative recombination to improve device performance. As a result, the PCE of the 3-B-N-MB modified PSCs significantly enhanced ∼32.5 % as compared to that of the pristine one and the air stability of the device has also improved. The 3-B-N-MB modification provides a new strategy to enhance the efficiency and stability of all-inorganic perovskite solar cells.

Optimization of the performance of CsPbI2Br perovskite solar cells in air by adding polyethylene-graft-maleic anhydride and its mechanism

In this study, by adding Polyethylene-graft-maleic anhydride (PGMA) to the inorganic CsPbI2Br perovskite film, the coordination bonds and hydrogen bonds between PGMA and CsPbI2Br cooperate to passivate defects, regulate energy level and stabilize the perovskite structure and eventually improve the device performance. We systematically study the effects of PGMA addition on the morphology, structure, light absorption, defect concentration and carrier lifetime, hydrophobicity, and optical stability and room temperature black phase stability of CsPbI2Br films, and the photoelectric performance and air stability of PSCs, as well as their mechanism. The experimental results show that the addition of 3 wt% of PGMA greatly improves the photoelectric conversion efficiency (PCE) of CsPbI2Br PSCs by 40.19 % because of the synergistic passivation effects and energy level tuning. The hydrogen bonds between –CH2 in PGMA and I−/Br− in CsPbI2Br, along with the coordination of carbonyl groups with Cs+/Pb2+, improve carrier transport and collection by inactivating flaw and managing the level, reducing the non-radiative recombination losses. In addition, the PSCs with 3 wt% of PGMA maintain 80 % of their initial efficiency even after 600 h in high humidity air environment due to the synergistic effect of coordination bonds and hydrogen bonds. Our study provides valuable insights into the use of PGMA to improve the performance of all-inorganic CsPbI2Br PSCs and the practicality of perovskite solar cells.

Simultaneous Defect Passivation and Electric Level Regulation with Rubidium Fluoride for High-Efficiency CsPbI2Br Perovskite Solar Cells.

Due to the good balance of efficiency and stability, CsPbI2Br perovskite solar cells (PSCs) recently have attracted widespread attention. However, the improvement in photovoltaic performance for CsPbI2Br PSCs was mainly limited by massive defects and unmatched energy levels. Surface modification is the most convenient and effective strategy to decrease defect densities of perovskite films. Herein, we deposited rubidium fluoride (RbF) onto the surface of CsPbI2Br perovskite films by spin-coating. The numerous defects could be significantly passivated by RbF, resulting in suppressed nonradiative recombination. Furthermore, the CsPbI2Br perovskite film after RbF treatment exhibits a deeper Fermi level, and an additional built-in electric field forms to promote charge transport. Consequently, the champion device achieves a high efficiency of 10.82% with an improved VOC of 1.14 V, and it also exhibits excellent stability after long-term storage. This work offers a simple and effective approach to enhance the photovoltaic performance and stability of PSCs for broader applications in the future.

Multifunctional Interface Modification Enables Efficient and Stable HTL-Free Carbon-Electroded CsPbI2Br Perovskite Solar Cells.

In recent years, hole transport layer-free all-inorganic CsPbI2Br carbon-electroded perovskite solar cells (C-PSCs) have garnered significant attention due to a trade-off between stability and photovoltaic performance. However, there are inevitably many defects generated at the surfaces or grain boundaries of CsPbI2Br perovskite films, which will serve as carrier non-radiative recombination centers, and CsPbI2Br perovskite films are sensitive to water molecules to degrade, together with energy level mismatch between CsPbI2Br perovskite and carbon electrodes. Herein, 1-benzyl-3-methylimidazolium hexafluorophosphate (1-B-3-MIMPF6), an imidazolium-based ionic liquid simultaneously containing benzene ring and fluorine atoms, was introduced for the modification of the perovskite/carbon interface. The results showed that it could effectively reduce defects, enhance carrier transfer, mitigate carrier non-radiative recombination, facilitate energy alignment, and block moisture intrusion. Therefore, the photovoltaic performance of the modified PSCs with ITO/SnO2/CsPbI2Br/1-B-3-MIMPF6/carbon architecture has been boosted with a champion power conversion efficiency (PCE) of 13.47 %, open circuit voltage of 1.20 V, short circuit current density of 14.69 mA/cm2, and fill factor of 76 %. Moreover, the unencapsulated modified devices exhibited an improved stability and the PCE maintained 78 % of their initial PCE after 24 h storage at room temperature in a 30 %-35 % humidity environment, whereas that of the pristine devices dropped to almost zero.

Phase transition mechanism of CsPbI2Br perovskite films induced by moisture

The humidity stability and phase transition mechanism of the all-inorganic perovskite CsPbI2Br based on an optimized dual-source co-evaporation preparation process are investigated at the film interface level. It is found that the CsPbI2Br films annealed at 300 °C for several minutes exhibit a best crystallinity and photoelectric properties. The as-grown CsPbI2Br film is confirmed to be a α phase with a dark brown cubic crystal structure and an average visible transparency of 35.9%. But it will be transformed into its δ phase with a transparent orthorhombic crystal structure and an average visible transparency of 80.3% after a certain amount of moisture exposure. Compared with the α phase film, the electronic structure of the δ phase has also changed significantly with a VBM shift of about 0.32 eV to high binding energy. The results of AR-XPS show that the water molecules in perovskite CsPbI2Br after a moisture exposure only adsorb on the surface rather than penetrate the interior of the lattice. When water molecules adsorb on the lattice surface, halide ions should migrate towards the lattice surface due to their high hydration enthalpy, resulting in halide vacancies within the lattice and causing the reduction of energy barrier for phase transition from α phase to δ phase. So the CsPbI2Br film will transform from its α phase to δ phase induced by water vapor, and this phase transition will be reversed to some extent after another annealing.

Improvement in stability and exploring the photovoltaic properties of CsPbI2Br thin films for perovskite solar cells

The phase stability and quality of CsPbI2Br perovskite film directly determines the performance of perovskite solar cells (PSCs). However, there is a lack of research on phase stability of perovskite films of PSCs. Here, by simply controlling precursors with specified ratios and solvents, the phase stability, charge transfer resistance and electron lifetime improve significantly which is useful for high performance in perovskite solar cells. Besides this, the information about trap centres by a novel technique Charge Deep Level Transient Spectroscopy (Q-DLTS) also helps to improve efficiency of perovskite solar cells. In this work, CsPbI2Br perovskite thin films have been synthesized using simple solution processing method, by varying CsBr and PbI2 precursors with specified ratios of 1.05 M:1 M and 1.10 M:1 M in Dimethysulfoxide (DMSO) and Dimethyl formamide (DMF). The CsPbI2Br film with ratio of 1.05:1 has more phase stability in ambient air at room temperature than that of 1.10:1. Drop casting method was adopted for thin films preparation and structurally cubic phase of perovskite films obtained by X-ray diffraction (XRD). Scanning electron microscope (SEM) showed more homogeneity on the surface of the sample with ratio 1.05:1 and energy dispersive x-ray spectroscopy (EDX) confirmed the presence of same amounts in chemical composition. Fourier transform infrared spectroscopy (FTIR) transmittance spectra showed that main peak is generally observed because of stretching vibrations of lead-iodide ions. In UV–visible (UV-Vis) little effect was observed on the energy band gaps i.e. 1.93 eV for 1.05 M:1 M and 1.96 eV for 1.10 M:1 M. The electrochemical impedance spectroscopy (EIS) measurements were performed for electronic charges accumulation on the surface of the films which showed semi-circles Nyquist plots and frequency dependent Bode plots were used to find electron lifetime. The charge transfer resistance (Rct) decreased from 52Ω to 45Ω and electron life time were approximately equal to 0.10 s and 0.09 s for the ratio of 1.10:1 and 1.05:1. I-V measurements showed an Ohmic contact formation providing insights into defect concentrations with a linear response to applied bias. Recombination lifetimes were investigated using transient photovoltage (TPV) at various biases, no correlation between the applied bias and recombination lifetime was found. Q-DLTS indicated presence of 3 trap centers for the charge carriers which were actively responsible for degradation of the perovskite material, these traps serve as recombination centres that reduce the overall power conversion efficiency (PCE) of solar cells. Photoluminescence spectroscopy (PL) analysis was done to verify the energy bandgap value which was found similar in comparison to UV–VIS.

Fluorinated organic ammonium salt passivation for high-efficiency and stable inverted CsPbI2Br perovskite solar cells.

All-inorganic CsPbI2Br inverted perovskite solar cells (PSCs) have drawn increasing attention because of their outstanding thermal stability and compatible process with tandem cells. However, relatively low open circuit voltage (Voc) has lagged their progress far behind theoretical limits. Herein, we introduce phenylmethylammonium iodide and 4-trifluoromethyl phenylmethylammonium iodide (CFPMAI) on the surface of a CsPbI2Br perovskite film and investigate their passivation effects. It is found that CFPMAI with a -CF3 substituent significantly decreases the trap density of the perovskite film by forming interactions with the under-coordinated Pb2+ ions and effectively suppresses the non-radiative recombination in the resulting PSC. In addition, CFPMAI surface passivation facilitates the optimization of energy-level alignment at the CsPbI2Br perovskite/[6,6]-phenyl C61 butyric acid methyl ester interface, resulting in improved charge extraction from the perovskite to the charge transport layer. Consequently, the optimized inverted CsPbI2Br device exhibits a markedly improved champion efficiency of 14.43% with a Voc of 1.12V, a Jsc of 16.31 mA/cm2, and a fill factor of 79.02%, compared to the 10.92% (Voc of 0.95V) efficiency of the control device. This study confirms the importance of substituent groups on surface passivation molecules for effective passivation of defects and optimization of energy levels, particularly for Voc improvement.

Enhanced Efficiency and Stability of Inverted CsPbI2Br Perovskite Solar Cells via Fluorinated Organic Ammonium Salt Surface Passivation.

All-inorganic perovskite solar cells (PSCs) have recently received increasing attention due to their outstanding thermal stability. However, the performance of these devices, especially for the devices with a p-i-n structure, is still inferior to that of the typical organic-inorganic counterparts. In this study, we introduce phenylammonium iodides with different side groups on the surface of the CsPbI2Br perovskite film and investigate their passivation effects. Our studies indicate that the 4-trifluoromethyl phenylammonium iodide (CFPA) molecule with the -CF3 side group effectively decreases the trap density of the perovskite film by forming interactions with the undercoordinated Pb2+ ions and significantly inhibits the nonradiative recombination in the derived PSC, leading to an enhanced open-circuit voltage (Voc) from 0.96 to 1.10 V after passivation. Also, the CFPA post-treatment enables better energy-level alignment between the conduction band minimum of CsPbI2Br perovskite and [6,6]-phenyl C61 butyric acid methyl ester, thereby enhancing the charge extraction from the perovskite to the charge transport layer. These combined benefits result in a significant enhancement of the power conversion efficiency from 11.22 to 14.37% for inverted CsPbI2Br PSCs. The device without encapsulation exhibits a degradation of only ≈4% after 1992 h in a N2 glovebox.

Suppressing the Light‐Soaking Effect of CsPbI2Br‐Based p–i–n Perovskite Solar Cells

The light‐soaking (LS) effect has been reported to limit the accuracy and stability of device power output of perovskite solar cells (PSCs) and it is significant to develop effective approaches and strategies to eliminate the LS effect in PSCs. There are very few reports on suppressing the LS effect in CsPbI2Br‐based all‐inorganic PSCs. Herein, a method to eliminate the LS effect by synchronous passivation of anionic and cationic defects in CsPbI2Br perovskite film is demonstrated. The 4‐(chlorosulfonyl)benzoic acid (CSBA) is added into perovskite precursor and the in situ generation of I3 − effectively passivates the anionic halogen vacancy defects in CsPbI2Br. In the meantime, the Lewis base groups on CSBA coordinate with Cs+ and Pb2+ to passivate the cationic defects. This zwitterionic passivation effect of CSBA remarkably cuts off the path of defect‐induced charge recombination and thus eliminates the LS effect. This work offers a deep opinion for future researchers to modulate the LS effect of all‐inorganic PSCs.

Effect of passivation on buried interface of CsPbI2Br perovskite films

Passivation on the surface or interface is one of the key issues in fabricating the efficient and stable perovskite solar cells (PSCs). In this Letter, we report a way to passivate the buried interface on the perovskite film by optimizing the growth kinetics of the precursor film. A solvent-controlled growth (SCG) strategy of the precursor film is adopted, that is, inducing the solvent volatilization of the precursor film before high-temperature annealing. It is found that the solvent distribution of the precursor film is the key to the growth kinetics of perovskite films. The vacuum pretreated precursor film can obtain a dense buried interface to avoid the generation of small grains and pores at the interfaces of the perovskite/electron transport layer after high temperature crystallization. After passivation, non-radiative recombination in CsPbI2Br films is suppressed, accompanied by favorable carrier separation and extraction at the interface. The power conversion efficiency of all-inorganic CsPbI2Br carbon-based PSCs without a hole transport layer reaches 13.46%. The SCG strategy on the precursor films provides a way to passivate the buried interface of PSCs.

Phthalimide additive-promoted ambient fabrication of inorganic CsPbI2Br perovskite for highly efficient and stable solar cells

Iodine-rich inorganic halide perovskites (CsPbI3 and CsPbI2Br) hold a great promise for emerging perovskite solar cells due to their excellent optoelectronic properties. Nevertheless, the current high-performance iodine-rich perovskite films for PSCs are usually fabricated in inert condition. It is still a great challenge to prepare high-quality iodine-rich perovskite films under realistic ambient conditions. Herein, we demonstrate a simple and feasible strategy for fabricating high-quality CsPbI2Br perovskite film in fully ambient air by introducing phthalimide (PTM) additive into the CsPbI2Br precursor. The PTM introduction protects the CsPbI2Br precursor from the unwanted phase transition and retards the crystallization of perovskite, which greatly ameliorates the perovskite crystallization process and prevents the perovskite from the moisture damage. When an appropriate amount of PTM is introduced, a stable CsPbI2Br perovskite film with high crystallinity and large grains is obtained in ambient air. The fabricated carbon-based CsPbI2Br perovskite solar cell achieves a high efficiency of 13.95%. In addition, the unencapsulated device displays an excellent stability with 91% of the initial efficiency maintaining after 14 days aging under ambient air.

Interfacial modification to improve all-inorganic perovskite solar cells by a multifunctional 4-aminodiphenylamine layer

All-inorganic carbon-based perovskite solar cells (PSCs) offer low costs and a favorable balance between stability and power conversion efficiency (PCE). Although bulk perovskites are defect tolerant, the defect-mediated carrier nonradiative recombination at the interface between perovskite and carbon layers limits the device performance and stability. In this study, a new 4-aminodiphenylamine (4-ADPA) interlayer was applied to modify the surface and grain boundaries of CsPbI2Br perovskite films. The 4-ADPA layer passivated defects by binding with undercoordinated lead and halide ions at the surface, resulting in the improved thin film quality, reduced defects, and suppressed carrier recombination. All-inorganic CsPbI2Br PSCs by 4-ADPA passivation achieved a PCE of 11.16% with reduced hysteresis and open-circuit voltage loss. In addition, the 4-ADPA passivation inhibited the degradation of the perovskite films in ambient conditions. After storing in air at 25 °C and 25% relative humidity for 700 h, the unpackaged PSC retains 80% of the original PCE. The all-inorganic PSCs with greatly improved device performance and stability would have great prospects in practical applications.

Water-soluble Ag2S QD modified CsPbI2Br heterojunction photodetector with ultra-low dark current and ultra-fast response speed

Mixed halide inorganic perovskite CsPbI3-xBrx has attracted attention in the field of optoelectronics. As a desirable photoactive material, the application of CsPbI2Br in the field of photodetector (PD) remains to be explored. The synergistic passivation strategy based on Ag2S quantum dot (QD) aqueous solution improves the morphology of the CsPbI2Br perovskite film. At the same time, Ag2S/CsPbI2Br bulk heterojunction optimizes the energy level arrangement between perovskite and Au electrode, improves the carrier transmission and collection capacity, and thus improves the performance of PD. Ag2S/CsPbI2Br bulk heterojunction PD has an ultra-low dark current of 7.74 pA, an ultra-fast response speed of 2.95/3.07 μs, and a high switching ratio of 7.67 × 105. This work provides a method for the preparation of high-quality mixed halide perovskite materials and a strategy for the development of high-performance perovskite PDs based on bulk heterojunction.

An ultrafast x-ray photoelectric detector using CsPbI2Br perovskite film

Metal halide perovskites have attracted worldwide attention in the field of x-ray detection due to their effective light absorption, excellent optoelectronic yield, high charge carrier mobility, and facile solution-processed preparation. Most of the current metal halide perovskite x-ray detectors rely on photoconductive or photovoltaic effects. In this work, we use CsPbI2Br perovskite films to demonstrate an ultrafast x-ray detector based on the photoelectric effect. The photoelectric effect allows the detector to exhibit a temporal resolution of 170 ps and an ultra-low dark current (10−5–10−3 pA), and the temporal response is the fastest among the reported perovskite x-ray detectors. The detector also exhibits a detectivity of 1.28 × 1010 Jones and a noise equivalent power of 6.95 × 10−11 W Hz−1/2. This ultrafast x-ray photoelectric detector has been utilized to diagnose x-ray flux in inertial confinement fusion experiments.

Improving the stability and efficiency of inorganic CsPbI2Br perovskite via surface reconstruction strategy

Inorganic CsPbX3 (X = Cl, Br, I) perovskite without volatile organic components in crystal lattice, has outstanding thermal stability and broad application prospects. Various strategies have been adopted to restrain the notorious phase transition process (from cubic to orthorhombic phase) for high photoelectric conversion efficiency (PCE). Nevertheless, most studies simply focus on the surface passivation of perovskite films, ignoring the influence of surface element segregation, which is inevitable during perovskite crystallization and growth process. Herein, 2-thiopheneacetic acid (2-TPAA) was adopted to reconstruct the surface of CsPbI2Br film via secondary growth process. The constituent elements of CsPbI2Br especially Br- enrich on the surface under the action of 2-TPAA. Meanwhile, the carboxyl and thiophene groups of 2-TPAA bidentate anchor Pb2+ ions respectively, forming protective layer to inhibit the invasion of external factors. In addition, the film morphology, moisture resistance, thermodynamic stability as well as carrier transport performance of perovskite films also get improved significantly. The black phase of CsPbI2Br survives in air ambient for several days, via the synergism of surface reconstruction and passivation effect. Furthermore, the device PCE increased to 15.03%, and retained 90% initial PCE during 400 d aging. The surface reconstruction strategy provides a convenient method to improve the phase stability of CsPbI2Br perovskite films in air ambient.

Low temperature-processed stable and high-efficiency carbon-based CsPbI2Br perovskite solar cells by additive strategy

All-inorganic perovskite solar cells require high-temperature preparation processes, which severely hinders their further commercial development. Inorganic perovskite materials have a high crystallization barrier, so the crystallinity is poor under low temperature conditions, resulting in poor device performance. Therefore, it is an important challenge to develop an excellent low-temperature preparation process. In this paper, the crystallization kinetics of the CsPbI2Br perovskite film under low temperature conditions was studied, and it was found that the perovskite was not completely crystallized during low temperature crystallization, and PbI2 remained. The PbI2 residue not only caused the appearance of lead defects but also formed insoluble CsBr due to the insufficient reaction of the raw materials. Through the interaction between the organic molecules 3-Amino-3-(3-pyridyl)propionic Acid (PA) and PbI2, the crystallization reaction process can be effectively improved. Eliminating the residual PbI2 also effectively inhibited the precipitation of CsBr, thereby significantly improved the crystallinity of CsPbI2Br. Efficiencies of 10.95% are achieved for low-temperature-processed CsPbI2Br planar-architecture FTO/SnO2/CsPbI2Br/carbon, and the obtained device also showed good stability in the air.

Cs2SnI6 nanocrystals enhancing hole extraction for efficient carbon-based CsPbI2Br perovskite solar cells

Carbon electrode-based perovskite solar cells (C-PSCs) promise long-term stability due to the chemically inertness and moisture resistance of carbon electrodes. However, the larger energy level mismatch between the perovskite and carbon electrode in C-PSCs results in lower hole extraction efficiency and poorer photovoltaic performance compared with the conventional metal electrode-based ones. In this work, a novel hole transport material (HTM) of Cs2SnI6 nanocrystals (CSI NCs) is synthesized and employed in CsPbI2Br C-PSCs. The suitable valence band maximum position of CSI (−5.55 eV) constitutes a gradient energy level alignment in CsPbI2Br/CSI/carbon, which effectively accelerates the hole extraction from perovskite to carbon electrode and reduces nonradiative recombination loss at the interface. With the introduction of CSI NC HTM between CsPbI2Br perovskite film and carbon electrode, the power conversion efficiency (PCE) of resulting cell devices are increased from 13.16% (Jsc of 14.17 mA cm−2, Voc of 1.221 V, FF of 76.05%) to 14.67% (Jsc of 14.51 mA cm−2, Voc of 1.267 V, FF of 79.81%). To the our best knowledge, this is the first time that CSI was used as a HTM in PSCs and it has shown attractive prospects in improving hole extraction efficiency and photovoltaic performance in resulting PSCs.

Gadolinium-incorporated CsPbI2Br for boosting efficiency and long-term stability of all-inorganic perovskite solar cells

All-inorganic CsPbI2Br perovskite solar cells (PSCs) have received extensive research interests recently. Nevertheless, their low efficiency and poor long-term stability are still obstacles for further commercial application. Herein, we demonstrate that high efficiency and exceptional long-term stability are realized by incorporating gadolinium(III) chloride (GdCl3) into the CsPbI2Br perovskite film. The incorporation of GdCl3 enhances the Goldschmidt tolerance factor of CsPbI2Br perovskite, yielding a dense perovskite film with small grains, thus the α-phase CsPbI2Br is remarkably stabilized. Additionally, it is found that the GdCl3-incorporated perovskite film achieves suppressed charge recombination and appropriate energy level alignment compared with the pristine CsPbI2Br film. The noticeable increment in efficiency from 14.01% (control PSC) to 16.24% is achieved for GdCl3-incorporated PSC. Moreover, the nonencapsulated GdCl3-incorporated PSC exhibits excellent environmental and thermal stability, remaining over 91% or 90% of the original efficiency after 1200 h aging at 40% relative humidity or 480 h heating at 85 °C in nitrogen glove box respectively. The encapsulated GdCl3-incorporated PSC presents an improved operational stability with over 88% of initial efficiency under maximum power point (MPP) tracking at 45 °C for 1000 h. This work presents an effective ion-incorporation approach for boosting efficiency and long-term stability of all-inorganic PSCs.

2D Non‐Layered In2S3 as Multifunctional Additive for Inverted Organic‐Free Perovskite Solar Cells with Enhanced Performance

Organic‐free perovskite solar cells (PSCs) have been of rising interest due to their remarkable resistance toward long‐term thermal stress. Nevertheless, the inorganic perovskite films usually suffer from poor crystallization and high‐density defects in bulk and near/at the interfaces, which leads to significant charge recombination loss and hence inferior device performance. Herein, it is demonstrated that high‐quality CsPbI2Br perovskite films could be prepared by using 2D non‐layered materials as additives, such as In2S3 nanoflakes (Nano‐In2S3) with well‐matched lattices and unsaturated dangling bonds on the surface. In addition, it is found that the introduction of Nano‐In2S3 results in not only defect passivation but also remarkable quasi‐Fermi level splitting across the perovskite film due to its gradient doping behavior, thereby enhancing the built‐in electric field in the inverted PSCs. As a result, the optimal devices based on Nano‐In2S3:CsPbI2Br absorber and all‐inorganic interfacial layers deliver a champion power conversion efficiency of 15.17% along with excellent ambient and thermal stabilities, superior to those of the pristine devices and comparable to the best organic‐free PSCs. A novel strategy for highly efficient and stable organic‐free photovoltaics by using 2D non‐layered materials as multifunctional additives is demonstrated.

On the role of carboxylated polythiophene in defect passivation of CsPbI 2 Br surface for efficient and stable all‐inorganic perovskite solar cells

Improved film surface is a prerequisite to achieve high photovoltaic performance of inorganic perovskite solar cells because defective (under-coordinated) lead ions derived from imperfect lattice structure of the film surface or grain boundaries the principal nonradiative recombination centers in the inorganic perovskite absorber. In this study, we suggest poly[3-(4-carboxybutyl)thiophene-2,5-diyl] (P3CT), a carboxylated p-type conjugated polymer, as a passivating agent of the CsPbI2Br layer to tailor electronic properties of a perovskite absorber. With the P3CT passivation, the defective sites of the perovskite film surface were improved and stabilized, which can suppress nonradiative recombination to promote charge transport of CsPbI2Br-based all-inorganic perovskite solar cells. Consequently, the P3CT passivation delivers a power conversion efficiency (PCE) of 12.25% and decent long-term stability of CsPbI2Br perovskite solar cells, which surpasses the pristine device without the passivation. The electricity generation capability under indoor light source of the passivated device is also studied, demonstrating a promising PCE of 27.47%. This work unveils the role of P3CT as a passivating agent to passivate the defective sites of CsPbI2Br perovskite film surface and grain boundaries, which facilitates charge transport and reduced carrier recombination of CsPbI2Br absorber in solar cell devices.