JIALINGBO

A facile immersing and washing strategy (I‐method) is reported to prepare effective organic monomolecular layers (MLs) as hole transport layers (ML‐HTLs). The I‐method can largely reduce the process cost as well as realize batch preparation of ML‐HTLs. Perovskite solar cells based on ML‐HTLs show improved power conversion efficiency and stability.

Hole transport materials and their processing occupy at least one‐third of the cost of perovskite solar cells (PSCs), which leaves plenty of room to improve the process of device fabrication. Herein, a facile immersing and washing strategy (I‐method) is reported to prepare effective organic monomolecular layers (MLs) of poly[N ,N ′‐bis(4‐butylphenyl)‐N ,N ′‐bis(phenyl) benzidine] (polyTPD) as hole transport layers (ML‐HTLs) to construct cost‐effective planar inverted PSCs. The ML enables an enhanced wettability to perovskite precursors and thus results in the growth of compact and uniform perovskite films. In addition, the ML exhibits better energy‐level alignment with perovskite. Consequently, the ML‐polyTPD‐based PSCs deliver significantly enhanced power conversion efficiency (PCE) and reproducibility, as compared to that of pristine polyTPD based devices. The practical consumption of polyTPD during the I‐method is cut to the bone, with the cost of $0.8 for 1 m² substrate being achieved, which is 0.15% of that by S‐method. The developed I‐method is facile, and time‐ and cost‐saving with low requirement for facilities as well as with low temperature and solution processability. This strategy is cost‐effective to prepare ML‐HTLs for large‐area and flexible PSCs with competitive photovoltaic performance and enhanced reproducibility.

Soft routed benzimidazole clubbed phenoxazine‐based organic ionic plastic crystals with iodide and bromide anions successfully introduced as hole transporting materials in perovskite solar cells yield power conversion efficiencies exceeding 18%, which represents the best alternative to existing spiro‐OMeTAD due to high conductivity and hole mobility with a safer, stable, and efficient system.

Abstract

Organic ionic plastic crystals (OIPCs) are synthesized through a simple metal‐free, cost‐effective approach. The strategized synchronization of electron‐rich phenoxazine with benzimidazolium iodide (OIPC‐I) and bromide (OIPC‐Br) salts lead to enhanced hole mobility and conductivity of OIPCs which is suitable for an efficient alternative to conventional organic hole transporting materials (HTMs) for stable perovskite solar cells (PSCs). The fabricated PSCs with OIPC‐I as hole transporting layer yielded a power conversion efficiency of 15.0% and 18.1% without and with additive (Li salt) respectively, which are comparable with spiro‐OMeTAD based devices prepared under similar conditions. Furthermore, the PSCs with OIPCs show good stability compared to the spiro‐OMeTAD with or without additives. Here, first time benzimidazolium‐based OIPCs have been used as an alternative organic HTM for perovskite solar cells, which opens a window for the design of effective OIPCs for highly efficient PSCs with long‐term stability.

A well‐designed inorganic–organic double hole transporting layer (HTL) based on inorganic CuSCN and organic polymer dithiophene‐benzene is developed. A perovskite solar cell with this dopant‐free HTL exhibits a very high power conversion efficiency of 22.0% (certified: 21.7%) and significantly improved thermal, humidity, and light stabilities compared to 2,2′,7,7′‐tetrakis(N ,N‐di‐p‐methoxyphenylamine)‐9,9‐spirobifluorene (Spiro‐OMeTAD) HTL‐based devices.

Abstract

Most of the high performance in perovskite solar cells (PSCs) have only been achieved with two organic hole transporting materials: 2,2′,7,7′‐tetrakis(N ,N‐di‐p‐methoxyphenylamine)‐9,9‐spirobifluorene (Spiro‐OMeTAD) and poly(triarylamine) (PTAA), but their high cost and low stability caused by the hygroscopic dopant greatly hinder the commercialization of PSCs. One effective alternative to address this problem is to utilize inexpensive inorganic hole transporting layer (i‐HTL), but obtaining high efficiency via i‐HTLs has remained a challenge. Herein, a well‐designed inorganic–organic double HTL is constructed by introducing an ultrathin polymer layer dithiophene‐benzene (DTB) between CuSCN and Au contact. This strategy not only enhances the hole extraction efficiency through the formation of cascaded energy levels, but also prevents the degradation of CuSCN caused by the reaction between CuSCN and Au electrode. Furthermore, the CuSCN layer also promotes the formation of a pinhole‐free and compact DTB over layer in the CuSCN/DTB structure. Consequently, the PSCs fabricated with this CuSCN/DTB layer achieves the power conversion efficiency of 22.0% (certified: 21.7%), which is among the top efficiencies for PSCs based on dopant‐free HTLs. Moreover, the fabricated PSCs exhibit high light stability under more than 1000 h of light illumination and excellent environmental stability at high temperature (85 °C) or high relative humidity (>60% RH).

Ambipolar black phosphorene (BP) nanosheets with tailored thicknesses concurrently enhance carrier extraction at both the electron‐transport layer/perovskite and hole‐transport layer/perovskite interfaces for high‐efficiency perovskite solar cells, demonstrating the appealing implementation of BP as a dual‐functional carrier‐transport material for a diversity of optoelectronic devices, including solar cells, photodetectors, sensors, light‐emitting diodes, etc.

Abstract

2D black phosphorene (BP) carries a stellar set of physical properties such as conveniently tunable bandgap and extremely high ambipolar carrier mobility for optoelectronic devices. Herein, the judicious design and positioning of BP with tailored thickness as dual‐functional nanomaterials to concurrently enhance carrier extraction at both electron transport layer/perovskite and perovskite/hole transport layer interfaces for high‐efficiency and stable perovskite solar cells is reported. The synergy of favorable band energy alignment and concerted cascade interfacial carrier extraction, rendered by concurrent positioning of BP, delivered a progressively enhanced power conversion efficiency of 19.83% from 16.95% (BP‐free). Investigation into interfacial engineering further reveals enhanced light absorption and reduced trap density for improved photovoltaic performance with BP incorporation. This work demonstrates the appealing characteristic of rational implementation of BP as dual‐functional transport material for a diversity of optoelectronic devices, including photodetectors, sensors, light‐emitting diodes, etc.

A novel polymer additive polyaniline (PANI) is introduced to the CsPbI₂Br film of the carbon‐based all‐inorganic perovskite solar cell. The PANI effectively balances the electron and hole transport, passivates defects, and improves film quality, resulting in reduced E _loss and high V _oc of 1.33 V and power conversion efficiency (PCE) of 13.52%.

The energy loss of all‐inorganic metal halide perovskite solar cells is large, which reduces the open‐circuit voltage and photoelectron conversion efficiency of the device. Herein, it is found that the cathode electron transfer speed is much lower than the anode hole transfer speed in CsPbI₂Br perovskite solar cell with fluorine‐doped tin oxide (FTO) glass/SnO₂/CsPbI₂Br/carbon structure, which induces charge accumulation at the cathode and energy loss of the device accordingly. By introducing a new conductive polymer additive polyaniline (PANI) to the CsPbI₂Br film, the electron transfer speed at the cathode is enhanced, resulting in balanced charge transfer at both electrodes and reduced energy loss of the device. Ultraviolet photoelectron spectroscopy measurement reveals that the PANI pushes the conduction band minimum of CsPbI₂Br upward, leading to stronger driving force for electron extraction. Therefore, the nonradiative recombination at the SnO₂/CsPbI₂Br interface is greatly suppressed. In addition, PANI can also effectively passivate defects and promote the crystal quality of CsPbI₂Br, leading to reduced nonradiative recombination in perovskite materials. Accordingly, the optimized all‐inorganic CsPbI₂Br solar cell delivers a high V _oc of 1.33 V and power conversion efficiency (PCE) of 13.52%.

CsPbI₃ inorganic perovskite exhibits some special unique properties including crystal structure distortion and quantum confinement effect, yet the poor phase stability severely hinders its application. The nature of the photoactive CsPbI₃ phase transition from the perspective of PbI₆ octahedral rotation is revealed and a facile method to simultaneously stabilize the photo‐active phase and reduce the defect density of CsPbI₃ is developed.

Abstract

CsPbI₃ inorganic perovskite has exhibited some special properties particularly crystal structure distortion and quantum confinement effect, yet the poor phase stability of CsPbI₃ severely hinders its applications. Herein, the nature of the photoactive CsPbI₃ phase transition from the perspective of PbI₆ octahedra is revealed. A facile method is also developed to stabilize the photoactive phase and to reduce the defect density of CsPbI₃. CsPbI₃ is decorated with multifunctional 4‐aminobenzoic acid (ABA), and steric neostigmine bromide (NGBr) is subsequently used to further mediate the thin films' surface (NGBr‐CsPbI₃(ABA)). The ABA or NG cation adsorbed onto the grain boundaries/surface of CsPbI₃ anchors the PbI₆ octahedra via increasing the energy barriers of octahedral rotation, which maintains the continuous array of corner‐sharing PbI₆ octahedra and kinetically stabilizes the photoactive phase CsPbI₃. Moreover, the added ABA and NGBr not only interact with shallow‐ or deep‐level defects in CsPbI₃ to significantly reduce defect density, but also lead to improved energy‐level alignment at the interfaces between the CsPbI₃ and the charge transport layers. Finally, the champion NGBr‐CsPbI₃(ABA)‐based inorganic perovskite solar cell delivers 18.27% efficiency with excellent stability. Overall, this work demonstrates a promising concept to achieve highly phase‐stabilized inorganic perovskite with suppressed defect density for promoting its optoelectronic applications.

Defect Passivation

In article number 1900529, Qinye Bao and co‐workers propose a strategy using abundant and color organic dyes as an additive to passivate defect states and to produce more n‐type perovskite films, which remarkably increases the power conversion efficiency of perovskite solar cells. The rich hydrogen bonds and carbonyl structures in the organic dye can significantly enhance the device stability both in terms of humidity and thermal stress.

The incorporation of potassium can remarkably stabilize wide‐bandgap perovskites with a high Br content by the synergistic effect of the formation of 2D K₂PbI₄ at the grain boundaries and the interstitial occupancy in the perovskite lattices, which can effectively reduce the trap density and inhibit ion migration, thus suppressing the nonradiative recombination and photoinduced phase segregation.

Wide‐bandgap perovskites have great potential to enable high‐efficiency tandem photovoltaics by combining with the well‐established low‐bandgap absorbers. However, such wide‐bandgap perovskites are often necessarily constructed with a high Br content, and thus faced with issues of phase segregation–induced photoinstability and high defect density, severely hindering their photovoltaic performance. Herein, a remarkable boost of the stability and efficiency of wide‐bandgap perovskite solar cells (PSCs) is demonstrated by simply incorporating potassium ions. Experiments have shown the interstitial occupancy of potassium ions in the perovskite lattice and the formation of 2D K₂PbI₄ at the grain boundaries, both can reduce the trap density and inhibit ion migration, and thus suppress nonradiative recombination and photoinduced phase segregation. The average power conversion efficiency (PCE) of photovoltaic devices based on the perovskite with 40% Br is improved from 15.28% to 17.94%, among which the champion efficiency is 18.38% with an optimal 15% KI incorporation. Importantly, the champion open‐circuit voltage (V _oc) remains unchanged (≈1.25 V) even when the bandgap reduces from 1.80 to 1.75 eV due to KI doping, effectively reducing the V _oc deficit. In addition, the unencapsulated cells can sustain 94% of the initial PCE after 2000 h of storage in ambient atmosphere, affirming their outstanding stability.

A straightforward approach is developed to decouple the degradation effects occurring at the interfaces between the lead halide absorber with a hole‐transport and electron‐transport layers in perovskite solar cells. The impact of the hole‐transport layer is shown to depend on its composition: materials such as nickel oxide aggressively interact with the perovskite, whereas organic polytriarylamine provides a stable interface.

There is growing evidence that the stability of perovskite solar cells (PSCs) is strongly dependent on the interface chemistry between the absorber films and adjacent charge‐transport layers, whereas the exact mechanistic pathways remain poorly understood. Herein, a straightforward approach is presented for decoupling the degradation effects induced by the top fullerene‐based electron transport layer (ETL) and various bottom hole‐transport layer (HTL) materials assembled in p‐i‐n PSCs. It is shown that chemical interaction of MAPbI₃ absorber with ETL comprised of the fullerene derivative most aggressively affects the device operational stability. However, washing away the degraded fullerene derivative and depositing fresh ETL leads to restoration of the initial photovoltaic performance when bottom perovskite/HTL interface is not degraded. Following this approach, it is possible to compare the photostability of stacks with various HTLs. It is shown that poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) and NiO_x induce significant degradation of the adjacent perovskite layer under light exposure, whereas poly[bis(4‐phenyl)(2,4,6‐trimethylphenyl)amine] (PTAA) provides the most stable perovskite/HTL interface. A time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) analysis allows identification of chemical origins of the interactions between MAPbI₃ and HTLs. The proposed research methodology and the revealed degradation pathways should facilitate the development of efficient and stable PSCs.

The slow photon of CsPbBr₃ inverse opal (IO) and the localized surface plasmon resonance of Au nanoparticles are coupled synergistically to enhance the performance of inorganic perovskite solar cells (PSCs). The synergetic effect leads to the enhanced light absorption and more efficient carriers transfer process. The PSC‐based Au‐CsPbBr₃ IO delivers a stabilized power conversion efficiency as high as 8.08%.

Abstract

Although all‐inorganic CsPbBr₃ are considered an ideal candidate for inorganic perovskite solar cells (PSCs) owing to their outstanding thermal‐ and moisture‐resistance, it still suffers from unfavorable charge transfer process and limited light harvesting ability. Herein, CsPbBr₃ inverse opal (IO) films coupled with Au nanoparticles (NPs) are rationally designed, and PSCs based on Au‐CsPbBr₃ IO achieve a stabilized photoelectric conversion efficiency up to 8.08%. By selectively tuning IO pore diameter, the slow photon region of CsPbBr₃ IO and localized surface plasmon resonance (SPR) region from Au NPs can be modulated to be overlapped to enhance the performance of inorganic CsPbBr₃ PSCs. The synergetic effect devotes to light utilization and charge transfer process, resulting in an enhanced light absorption capability and suppressed recombination rate of photogenerated electron–hole pairs. The introduction of Au not only triggers SPR effect, but also enhances efficient separation/injection of charge carriers owing to the Schottky barriers. Furthermore, it is revealed that simultaneous effect from SPR and IO photon effect are conducive to reduce exciton binding energy, enhancing exciton dissociation efficiency and leading to significant increase in free carrier density. This work provides a rational strategy for plasmonic metal/semiconductor composite light‐absorber for high‐performance inorganic PSCs.

Interface energetics in 2D Ruddlesden–Popper perovskite solar cells are systematically investigated. The potential gradient across ligands that significantly decreases surface work function, promotes separation of the photogenerated charge carriers with electron transferring from perovskite crystal to ligand at the interface, suppressing the charge recombination and thus enhancing the open‐circuit voltage.

Abstract

2D Ruddlesden–Popper perovskites (RPPs) are emerging as potential challengers to their 3D counterpart due to superior stability and competitive efficiency. However, the fundamental questions on energetics of the 2D RPPs are not well understood. Here, the energetics at (PEA)₂(MA) _{n −1}Pb _n I_{3 n +1}/[6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM) interfaces with varying n values of 1, 3, 5, 40, and ∞ are systematically investigated. It is found that n–n junctions form at the 2D RPP interfaces (n = 3, 5, and 40), instead of p–n junctions in the pure 2D and 3D scenarios (n = 1 and ∞). The potential gradient across phenethylammonium iodide ligands that significantly decreases surface work function, promotes separation of the photogenerated charge carriers with electron transferring from perovskite crystal to ligand at the interface, reducing charge recombination, which contributes to the smallest energy loss and the highest open‐circuit voltage (V _oc) in the perovskite solar cells (PSCs) based on the 2D RPP (n = 5)/PCBM. The mechanism is further verified by inserting a thin 2D RPP capping layer between pure 3D perovskite and PCBM in PSCs, causing the V _oc to evidently increase by 94 mV. Capacitance–voltage measurements with Mott–Schottky analysis demonstrate that such V _oc improvement is attributed to the enhanced potential at the interface.

Deuterium oxide as a solvent additive enhances the power conversion efficiency of triple‐cation perovskite solar cells. It passivates the defects, thus enhancing the charge carrier lifetimes and diffusion lengths. Partial formamidinium deuteration also helps to stabilize the PbI₆ structure. This facile approach based on selective isotope exchange could possibly be extended to other perovskite devices to improve their optoelectronic properties.

Abstract

Heavy water or deuterium oxide (D₂O) comprises deuterium, a hydrogen isotope twice the mass of hydrogen. Contrary to the disadvantages of deuterated perovskites, such as shorter recombination lifetimes and lower/invariant efficiencies, the serendipitous effect of D₂O as a beneficial solvent additive for enhancing the power conversion efficiency (PCE) of triple‐A cation (cesium (Cs)/methylammonium (MA)/formaminidium (FA)) perovskite solar cells from ≈19.2% (reference) to 20.8% (using 1 vol% D₂O) with higher stability is reported. Ultrafast optical spectroscopy confirms passivation of trap states, increased carrier recombination lifetimes, and enhanced charge carrier diffusion lengths in the deuterated samples. Fourier transform infrared spectroscopy and solid‐state NMR spectroscopy validate the N–H₂ group as the preferential isotope exchange site. Furthermore, the NMR results reveal the induced alteration of the FA to MA ratio due to deuteration causes a widespread alteration to several dynamic processes that influence the photophysical properties. First‐principles density functional theory calculations reveal a decrease in PbI₆ phonon frequencies in the deuterated perovskite lattice. This stabilizes the PbI₆ structures and weakens the electron–LO phonon (Fröhlich) coupling, yielding higher electron mobility. Importantly, these findings demonstrate that selective isotope exchange potentially opens new opportunities for tuning perovskite optoelectronic properties.

Sufficient and stable surface passivation of perovskite solar cells is realized using a novel tribenzylphosphine oxide molecule, with high cell efficiency of >22% and excellent operation stability being obtained. These achievements benefit from the strong molecule–perovskite Coulomb interaction and the formation of superstructure self‐assembly on the perovskite surface, enabled by intermolecular π–π conjugation.

Abstract

Surface passivation is an effective approach to eliminate defects and thus to achieve efficient perovskite solar cells, while the stability of the passivation effect is a new concern for device stability engineering. Herein, tribenzylphosphine oxide (TBPO) is introduced to stably passivate the perovskite surface. A high efficiency exceeding 22%, with steady‐state efficiency of 21.6%, is achieved, which is among the highest performances for TiO₂ planar cells, and the hysteresis is significantly suppressed. Further density functional theory (DFT) calculation reveals that the surface molecule superstructure induced by TBPO intermolecular π–π conjugation, such as the periodic interconnected structure, results in a high stability of TBPO–perovskite coordination and passivation. The passivated cell exhibits significantly improved stability, with sustaining 92% of initial efficiency after 250 h maximum‐power‐point tracking. Therefore, the construction of a stabilized surface passivation in this work represents great progress in the stability engineering of perovskite solar cells.

How fluorine atoms substitute the aromatic ring of spacer cations has subtle influence in the final device performance based on 2D/3D hybrid perovskites. Hydrophobic ortho‐ , meta‐ , and para‐ fluorophenyl groups act as the protective umbrella to prevent the recombination and invasion of water. The resulting devices exhibit high V _OC and good air stability.

The notoriously poor stability of organic–inorganic hybrid perovskite solar cells is a crucial issue restricting the commercial application of such burgeoning technology. Passivation of bulk perovskite absorber by fluorinated aromatic ammonium salt via low‐dimensional perovskites has been proved to be an effective way of improving stability and efficiency. Herein, the influence of fluorination position (ortho‐ , meso‐ , and para‐ ) on the aromatic moiety is studied in terms of their dipole moments and the ability to reduce defect density, extend carrier lifetimes, and assist charge transfer. In addition to the improved power conversion efficiency (PCE) from 19.17% to above 20%, the device treated with 2‐(o‐fluorophenyl)ethylamine iodide exhibits a remarkable open‐circuit voltage (V _OC) of 1.21 V. While the 2‐(p‐fluorophenyl)ethylamine iodide‐treated device shows only 1% loss of its initial value under ambient atmosphere (with RH of 10–30%) without encapsulation for 1440 h storage. The molecular structure of fluorinated aromatic cations plays multiple roles in passivating the interface of the perovskite device.

A facile immersing and washing strategy (I‐method) is reported to prepare effective organic monomolecular layers (MLs) as hole transport layers (ML‐HTLs). The I‐method can largely reduce the process cost as well as realize batch preparation of ML‐HTLs. Perovskite solar cells based on ML‐HTLs show improved power conversion efficiency and stability.

Hole transport materials and their processing occupy at least one‐third of the cost of perovskite solar cells (PSCs), which leaves plenty of room to improve the process of device fabrication. Herein, a facile immersing and washing strategy (I‐method) is reported to prepare effective organic monomolecular layers (MLs) of poly[N ,N ′‐bis(4‐butylphenyl)‐N ,N ′‐bis(phenyl) benzidine] (polyTPD) as hole transport layers (ML‐HTLs) to construct cost‐effective planar inverted PSCs. The ML enables an enhanced wettability to perovskite precursors and thus results in the growth of compact and uniform perovskite films. In addition, the ML exhibits better energy‐level alignment with perovskite. Consequently, the ML‐polyTPD‐based PSCs deliver significantly enhanced power conversion efficiency (PCE) and reproducibility, as compared to that of pristine polyTPD based devices. The practical consumption of polyTPD during the I‐method is cut to the bone, with the cost of $0.8 for 1 m² substrate being achieved, which is 0.15% of that by S‐method. The developed I‐method is facile, and time‐ and cost‐saving with low requirement for facilities as well as with low temperature and solution processability. This strategy is cost‐effective to prepare ML‐HTLs for large‐area and flexible PSCs with competitive photovoltaic performance and enhanced reproducibility.

CsPbI₃ inorganic perovskite exhibits some special unique properties including crystal‐structure distortion and quantum confinement effect, yet the poor phase stability severely hinders its application. The nature of the photoactive CsPbI₃ phase transition from the perspective of PbI₆ octahedral rotation is revealed and a facile method to simultaneously stabilize the photo‐active phase and reduce the defect density of CsPbI₃ is developed.

Abstract

CsPbI₃ inorganic perovskite has exhibited some special properties particularly crystal structure distortion and quantum confinement effect, yet the poor phase stability of CsPbI₃ severely hinders its applications. Herein, the nature of the photoactive CsPbI₃ phase transition from the perspective of PbI₆ octahedra is revealed. A facile method is also developed to stabilize the photoactive phase and to reduce the defect density of CsPbI₃. CsPbI₃ is decorated with multifunctional 4‐aminobenzoic acid (ABA), and steric neostigmine bromide (NGBr) is subsequently used to further mediate the thin films' surface (NGBr‐CsPbI₃(ABA)). The ABA or NG cation adsorbed onto the grain boundaries/surface of CsPbI₃ anchors the PbI₆ octahedra via increasing the energy barriers of octahedral rotation, which maintains the continuous array of corner‐sharing PbI₆ octahedra and kinetically stabilizes the photoactive phase CsPbI₃. Moreover, the added ABA and NGBr not only interact with shallow‐ or deep‐level defects in CsPbI₃ to significantly reduce defect density, but also lead to improved energy‐level alignment at the interfaces between the CsPbI₃ and the charge transport layers. Finally, the champion NGBr‐CsPbI₃(ABA)‐based inorganic perovskite solar cell delivers 18.27% efficiency with excellent stability. Overall, this work demonstrates a promising concept to achieve highly phase‐stabilized inorganic perovskite with suppressed defect density for promoting its optoelectronic applications.

The doping capability of conjugated polymer is governed by the degree of electronic coupling with the dopant. The high doping capability of conjugated polymers can be utilized to form an electric dipole layer at the surface of perovskite with a hole transporting layer, which facilitates charge extraction and enhances the performance of perovskite solar cells.

Abstract

Developing electrical organic conductors is challenging because of the difficulties involved in generating free charge carriers through chemical doping. To devise a novel doping platform, the doping capabilities of four designed conjugated polymers (CPs) are quantitatively characterized using an AC Hall‐effect device. The resulting carrier density is related to the degree of electronic coupling between the CP repeating unit and 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4‐TCNQ), and doped PIDF‐BT provides an outstanding electrical conductivity, exceeding 210 S cm⁻¹, mainly due to the doping‐assisted facile carrier generation and relatively fast carrier mobility. In addition, it is noted that a slight increment in the electron‐withdrawing ability of the repeating unit in each CP diminishes electronic coupling with F4‐TCNQ, and severely deteriorates the doping efficiency including the alteration of operating doping mechanism for the CPs. Furthermore, when PIDF‐BT with high doping capability is applied to the hole transporting layer, with F4‐TCNQ as the interfacial doping layer at the interface with perovskite, the power conversion efficiency of the perovskite solar cell improves significantly, from 17.4% to over 20%, owing to the ameliorated charge‐collection efficiency. X‐ray photoelectron spectroscopy and Kelvin probe analyses verify that the improved solar cell performance originates from the increase in the built‐in potential because of the generation of electric dipole layer.

Recent progress in inorganic lead‐based and lead‐free CsBX₃ perovskite solar cells using various strategies is reviewed and their prospects and challenges in the future are discussed in detail.

Abstract

All‐inorganic perovskite semiconductors have recently drawn increasing attention owing to their outstanding thermal stability. Although all‐inorganic perovskite solar cells (PSCs) have achieved significant progress in recent years, they still fall behind their prototype organic–inorganic counterparts owing to severe energy losses. Therefore, there is considerable interest in further improving the performance of all‐inorganic PSCs by synergic optimization of perovskite films and device interfaces. This review article provides an overview of recent progress in inorganic PSCs in terms of lead‐based and lead‐free composition. The physical properties of all‐inorganic perovskite semiconductors as well as the hole/electron transporting materials are discussed to unveil the important role of composition engineering and interface modification. Finally, a discussion of the prospects and challenges for all‐inorganic PSCs in the near future is presented.

This article gives comprehensive understanding and exploration of perovskite film thickness influence on its optical and electronic properties. The optical properties of films are verified by simulation and found correlated with experimental results as well as electronic properties are also matched with device performance.

The phenomenal optoelectronic properties of lead halide perovskites have spurred a remarkable worldwide effort to develop them as photovoltaic materials. The morphology and crystal structure of the films have a profound effect on the characteristics and performance of devices; however, the influence of underlying hole transport layers (HTLs) or electron transport layers (ETLs) and film thickness on the film morphology and electronic characteristics remains unclear. Herein, the characteristics of perovskite films with variable thickness are studied, including the morphological, crystal, optical properties and electronic band structure of these films using scanning electron microscopy (SEM), X‐ray diffraction (XRD), and UV–vis absorption spectra. The corresponding performance of perovskite solar cells (PSCs) devices is correlated with the different thicknesses of perovskite films. In addition, ultraviolet photoelectron spectroscopy (UPS) results show that for the optimized perovskite thickness (310 nm) the interfacial dipole (Δ) formed at the interface with the substrate reaches its highest value of 0.23 eV. Therefore, this strong dipole compared with other thicknesses allows the carriers to be swept out efficiently.

Cheap and efficient : Core‐twisted tetrachloroperylenediimides (ClPDIs) are synthesized as low‐cost (≈2 USD g⁻) and efficient organic non‐fullerene acceptors (NFAs) for perovskite solar cells (PSCs). The best‐performing device based on a ClPDI as electron‐transporting material (ETM) exhibits a power conversion efficiency of 17.3 %, which is comparable to that of 17.2 % for a reference cell with state‐of‐the‐art fullerene‐based ETM.

Abstract

Herein, core‐twisted tetrachloroperylenediimides (ClPDIs) were introduced as new efficient electron‐transporting materials (ETMs) to replace the commonly used fullerene acceptor PC₆₁BM in inverted planar perovskite solar cells (PSCs). ClPDI showed a low‐lying lowest unoccupied molecular orbital (LUMO) energy level of −3.95 eV, which was compatible with the conduction band of CH₃NH₃PbI_3−x Cl _x (−3.90 eV). In addition, the role of the length of the alkyl side chain at the imide position of ClPDI in modulating the molecular solubility, aggregation capacity for charge‐transport properties, surface hydrophobicity, and PSC performance was investigated. The device based on ClPDI‐C4 (ClPDI with n‐butyl side chains) as ETM achieved a maximum power conversion efficiency (PCE) of 17.3 % under standard AM 1.5G illumination, which iwas very competitive with that of the reference device employing PC₆₁BM/C₆₀ (PCE=17.2 %) as ETM. Moreover, the devices with ClPDIs as ETMs exhibited better device stability than that with PC₆₁BM/C₆₀. This work highlights the great potential of ClPDI derivatives as low‐cost (≈2.0 USD g⁻¹) and effective ETMs to obtain efficient solution‐processed inverted PSCs. This class of ClPDI derivatives is expected further promote the performance and stability of PSCs after extended investigation.