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Carbazole-based self-assembled monolayers have received considerable attention as hole-selective layers (HSLs) in inverted perovskite solar cells. As an HSL, the electron-blocking capability is important and directly related to electron affinity (EA). Low-energy inverse photoelectron spectroscopy (LEIPS) is the most reliable method for EA measurement. However, the intense electron-impact-induced fluorescence from carbazole interferes with their measurement. By improving the photon detector, we were able to measure 2PACz and MeO-2PACz LEIPS spectra and determine their respective EAs of 1.72 and 1.48 eV. These small EA values ensure effective electron-blocking capability of HSLs regardless of the type of perovskite layer. [ABSTRACT FROM AUTHOR]

In recent years, tin halide perovskite solar cells (PKSCs) have emerged as a promising alternative to lead‐PKSCs. However, due to defects such as Sn4+ and iodide vacancies, their efficiency is lower than lead‐PKSCs. To address this issue, various strategies are proposed to improve the quality of perovskite, including copper iodide (CuI) doping. Unfortunately, the conventional solvent composition of DMF:DMSO = 4:1 has limited the solubility of CuI, resulting in inconsistent results and limited efficiency improvements. However, this research proposed a preprocessing method of CuI to decrease the defects and improve the perovskite layer's morphology. As a result, the efficiency of tin‐PKSCs with both P‐I‐N and hole transport layer (HTL) free structures is enhanced, increasing from 9.8% to 13.1% and 9.4% to 10.5%, respectively. Moreover, the doped tin‐PKSCs have exhibited better stability, retaining 75% of their initial power conversion efficiency (PCE) after being stored in a glovebox for 102 days. [ABSTRACT FROM AUTHOR]

Further improvement of the performance and stability of inverted perovskite solar cells (PSCs) is necessary for commercialization. Here, ferrocene derivative dibenzoylferrocene (DBzFe) is used as an additive to enhance the performance and stability of MA‐ and Br‐ free PSCs. The results show that the introduction of DBzFe not only passivates the defects in the film but also inhibits the ion migration in the film. The final device achieves a power conversion efficiency (PCE) of 23.53%, which is one of the highest efficiencies currently based on self‐assembled monolayers (SAMs). Moreover, it maintains more than 96.4% of the original efficiency when running continuously for 400 h at the maximum power point. [ABSTRACT FROM AUTHOR]

The photoelectric properties of nontoxic Sn‐based perovskite make it a promising alternative to toxic Pb‐based perovskite. It has superior photovoltaic performance in comparison to other Pb‐free counterparts. The facile oxidation of Sn2+ to Sn4+ presents a notable obstacle in the advancement of perovskite solar cells that utilize Sn, as it adversely affects their stability and performance. The study revealed the presence of a Sn4+ concentration on both the upper and lower surfaces of the perovskite layer. This discovery led to the adoption of a bi‐interface optimization approach. A thin layer of Sn metal was inserted at the two surfaces of the perovskite layer. The implementation of this intervention yielded a significant decrease in the levels of Sn4+ and trap densities. The power conversion efficiency of the device was achieved at 14.31 % through the optimization of carrier transportation. The device exhibited operational and long‐term stability. [ABSTRACT FROM AUTHOR]

The photoelectric properties of nontoxic Sn‐based perovskite make it a promising alternative to toxic Pb‐based perovskite. It has superior photovoltaic performance in comparison to other Pb‐free counterparts. The facile oxidation of Sn2+ to Sn4+ presents a notable obstacle in the advancement of perovskite solar cells that utilize Sn, as it adversely affects their stability and performance. The study revealed the presence of a Sn4+ concentration on both the upper and lower surfaces of the perovskite layer. This discovery led to the adoption of a bi‐interface optimization approach. A thin layer of Sn metal was inserted at the two surfaces of the perovskite layer. The implementation of this intervention yielded a significant decrease in the levels of Sn4+ and trap densities. The power conversion efficiency of the device was achieved at 14.31 % through the optimization of carrier transportation. The device exhibited operational and long‐term stability. [ABSTRACT FROM AUTHOR]

This study is on the enhancement of the efficiency of wide bandgap (FA0.8Cs0.2PbI1.8Br1.2) perovskite solar cells (PSCs) used as the top layer of the perovskite/perovskite tandem solar cell. Poly[bis(4‐phenyl) (2,4,6‐trimethylphenyl) amine] (PTAA) and the monomolecular layer called SAM layer are effective hole collection layers for APbI3 PSCs. However, these hole transport layers (HTL) do not give high efficiencies for the wide bandgap FA0.8Cs0.2PbI1.8Br1.2 PSCs. It is found that the surface‐modified PTAA by monomolecular layer (MNL) improves the efficiency of PSCs. The improved efficiency is explained by the improved FA0.8Cs0.2PbI1.8Br1.2 film quality, decreased film distortion (low lattice disordering) and low density of the charge recombination site, and improves carrier collection by the surface modified PTAA layer. In addition, the relationship between the length of the alkyl group linking the anchor group and the carbazole group is also discussed. Finally, the wide bandgap lead PSCs (Eg = 1.77 eV) fabricated on the PTAA/monomolecular bilayer give a higher power conversion efficiency of 16.57%. Meanwhile, all‐perovskite tandem solar cells with over 25% efficiency are reported by using the PTAA/monomolecular substrate. [ABSTRACT FROM AUTHOR]

Environment‐friendly tin perovskite solar cells (T‐PKSCs) are the most suitable alternative candidate for lead‐free PKSCs. However, the photovoltaic performance of such T‐PKSCs is far below those of lead‐based perovskite solar cells due to an energetic mismatch between the perovskite layer and charge transport layers. Herein, it is shown that, by partial substitution of the A‐site cation using diethylammonium iodide (DEAI) substitution, deeper energy levels are obtained. At the same time, the trap density is reduced and the grain size is significantly improved. The fabricated solar cell shows much enhanced efficiency from 7.31% to 10.28%, short‐circuit current density from 18.68 to 21.69 mA cm−2, open‐circuit voltage from 0.59 to 0.67 V, and fill factor from 0.67 to 0.71 after DEAI substitution. Such an efficiency improvement can be explained by matching energy levels at the interfaces between perovskite layer and the charge transport layers. In addition, after 50 days of storage, the modified T‐PKSCs demonstrate high stability maintaining 78% of its initial efficiency, whereas the reference device degrades to 68% during 28 days storage. [ABSTRACT FROM AUTHOR]

Tin‐lead perovskite solar cells (PSCs) show inferior power conversion efficiency (PCE) than their Pb counterparts mainly because of the higher open‐circuit voltage (Voc) loss. Here, it is revealed that the p‐type surface of perovskite transforms to n‐type, based on post‐treatment by a Lewis base, ethylenediamine. This approach forms a graded band structure owing to the rise of the Fermi‐energy level at the surface of the perovskite layer, and increases the built‐in potential from 0.56 to 0.76 V, which increases the Voc by more than 100 mV. It is demonstrated that EDA can lower the defect density (Sn4+ amount) by screening perovskite against oxygen, and by bonding with undercoordinated Sn on the surface. This study further explores the role of Br anion inclusion in the perovskite lattice from the viewpoint of reducing the lattice strain and Urbach energy. Finally, a high Voc of 0.86 V is obtained, corresponding to a voltage deficit of 0.39 V, using a perovskite absorber with a bandgap of 1.25 eV and the highest PCE (21.74%) reported so far for Sn‐Pb PSCs is achieved. [ABSTRACT FROM AUTHOR]

Trap states at the interface or in bulk perovskite materials critically influence perovskite solar cells performance and long‐term stability. Here, a strategy for efficiently passivating charge traps and mitigating interfacial recombination by SnO2 surface sulfur functionalization is reported, which utilizes xanthate decomposition on the SnO2 surface at low temperature. The results show that functionalized sulfur atoms can coordinate with under‐coordinated Pb2+ ions near the interface. After device fabrication under more than 60 % humidity in ambient air, the efficiency of methylammonium lead iodide (MAPbI3) perovskite solar cells based on sulfur‐functionalized SnO2 increased from 16.56 % to 18.41 % with suppressed hysteresis, which resulted from the accelerated interfacial charge transport kinetics and decreased traps in bulk perovskite by interfacial sulfur functionalization. Additionally, thermally stimulated current studies show the decreased trap density in the shallow trap area after interfacial sulfur functionalization. The interfacial sulfur functionalized solar cells without sealing also exhibited considerable retardation of solar cell degradation with only 10 % degradation after 70 days air storage. This work demonstrates a facile sulfur functionalization strategy by using xanthate decomposition on SnO2 surfaces to obtain highly efficient perovskite solar cells. Inorganic sulfur functionalization has been realized through xanthate annealing on a SnO2 substrate, facilitating electron transport and reducing trap density at the shallow area. The efficiency of the resulting perovskite device was increased significantly with enhanced long‐term stability upon interfacial sulfur functionalization. This method is a simple and highly efficient means of interfacial functionalization with enhanced stability by using inorganic atoms. [ABSTRACT FROM AUTHOR]

Abstract: Compared with organic‐inorganic perovskites, all‐inorganic cesium‐based perovskites without volatile organic compounds have gained extensive interests because of the high thermal stability. However, they have a problem on phase transition from cubic phase (active for photo‐electric conversion) to orthorhombic phase (inactive for photo‐electric conversion) at room temperature, which has hindered further progress. Herein, novel inorganic CsPb1−xGexI2Br perovskites were prepared in humid ambient atmosphere without a glovebox. The phase stability of the all‐inorganic perovskite was effectively enhanced after germanium addition. In addition, the highest power conversion efficiency of 10.8 % with high open‐circuit voltage (VOC) of 1.27 V in a planar solar cell based on CsPb0.8Ge0.2I2Br perovskite was achieved. Furthermore, the highest VOC up to 1.34 V was obtained by CsPb0.7Ge0.3I2Br perovskite, which is a remarkable record in the field of all‐inorganic perovskite solar cells. More importantly, all the photovoltaic parameters of CsPb0.8Ge0.2I2Br perovskite solar cells showed nearly no decay after 7 h measurement in 50–60 % relative humidity without encapsulation. [ABSTRACT FROM AUTHOR]

Abstract: Perovskite solar cells have attracted considerable attention owing to their easy and low‐cost solution manufacturing process with high power conversion efficiency. However, the fabrication process is usually performed inside a glovebox to avoid moisture, as organometallic halide perovskites are easily dissolved in water. In this study, we propose a one‐step fabrication of high‐quality MAPbI3 perovskite films in around 50 % relative humidity (RH) humid ambient air by using diethyl ether as an antisolvent and methanol as an additive into this antisolvent. Because of the presence of methanol, the water molecules can be efficiently removed from the gaps of the perovskite precursors and the perovskite film formation can be slightly controlled, leading to pinhole‐free and low roughness films. Concurrently, methanol can be used to tune the DMSO ratio in the intermediate perovskite phase to regulate perovskite formation. Planar solar cells fabricated by using this method exhibited the best efficiency of 16.4 % with a reduced current density–voltage hysteresis. This efficiency value is approximately 160 % higher than the devices fabrication by using only diethyl ether treatment. From the impedance measurement, it is also found that the recombination reaction is suppressed when the device is prepared with methanol additive in the antisolvent. This method presents a new path for controlling the growth and morphology of perovskite films in humid climates and laboratories with uncontrolled environments. [ABSTRACT FROM AUTHOR]

Frequently observed high Voc loss in tin-lead mixed perovskite solar cells is considered to be one of the serious bottle-necks in spite of the high attainable Jsc due to wide wavelength photon harvesting. An amicable solution to minimize the Voc loss up to 0.50 V has been demonstrated by introducing an n-type interface with spike structure between the absorber and electron transport layer inspired by highly efficient Cu(In,Ga)Se2 solar cells. Introduction of a conduction band offset of ~0.15 eV with a thin phenyl-C61-butyric acid methyl ester layer (~25 nm) on the top of perovskite absorber resulted into improved Voc of 0.75 V leading to best power conversion efficiency of 17.6%. This enhancement is attributed to the facile charge flow at the interface owing to the reduction of interfacial traps and carrier recombination with spike structure as evidenced by time-resolved photoluminescence, nanosecond transient absorption, and electrochemical impedance spectroscopy measurements. [ABSTRACT FROM AUTHOR]

[Display omitted] • The monolayer together with PEDOT-PSS created an energetically aligned interface. • The monolayer and PEDOT-PSS bilayer plays a crucial role in improving performance. • The highest PCE of 8.66% of Sn wide bandgap perovskite has been achieved. 2PACz monolayer on PEDOT-PSS as the hole transport layer (HTL) was introduced to the inverted p-i-n Tin (Sn) based perovskite solar cells (PSCs) with 1.62 eV bandgap (Wide bandgap). 2PACz giving high efficiency to Pb perovskite solar cells was not effective at all for the Sn perovskite solar cells. We found that the efficiency was enhanced by synergistic effects of the 2PACz monolayer and PEDPT-PSS. The efficiency enhancement was explained by the compactness of the perovskite layer fabricated on bilayer consisting of 2PACz monolayer on PEDOT-PSS, an energetically aligned interface of the HTL/Sn-based perovskite absorber, the lower lattice disordering and reduced non-radiative recombination of the perovskite layer. The cell stability was improved by the compact surface morphology of the Sn perovskite fabricated on bilayer consisting of 2PACz monolayer on PEDOT-PSS and the suppression of direct contact between PEDOT-PSS and perovskite film. EDA 0.01 (GA 0.06 (FA 0.8 Cs 0.2) 0.94) 0.98 SnI 2 Br perovskite fabricated on bilayer consisting of 2PACz monolayer on PEDOT-PSS, gave the power conversion efficiency (PCE) of 8.66%, which is the highest performance for wide bandgap Sn perovskite solar cells reported so far. [ABSTRACT FROM AUTHOR]

Tin (Sn) based perovskite solar cells (PSCs) are rapidly getting attention due to their relatively less toxic nature compared to lead-PSCs. However, Sn perovskites previously reported are narrow-bandgap materials. Wide-bandgap perovskites, which are the key materials for the top layer of lead-free tandem solar cells, are rarely researched up to now. Here, it is demonstrated that optoelectronic properties of the GA 0.06 (FA 0.8 Cs 0.2) 0.94 SnI 2 Br based wide-bandgap perovskite can be improved by exploring (1) Germanium (II) Iodide (GeI 2) doping, (2) incorporation of Ethylenediamine Bromide (EDABr 2) at A site, (3) EDA passivation. The incorporation of big organic cation EDABr 2 in the wide-bandgap tin perovskite crystal structure together with GeI 2 doping made the carrier lifetime of perovskite absorber increase from 1.1 ns to 22.8 ns and the power conversion efficiency (PCE) was enhanced from 2.55% to 4.86% with an increment of Voc ˃ 100 mV. Further, we achieved the balanced charge transfer by using EDA passivation on the optimized perovskite surface film. As a result, the efficiency was improved from 4.86% to 7.50%, which is the highest efficiency among lead-free wide bandgap PSCs. This enhanced photovoltaic performance of the wide-bandgap tin perovskite device presents a wide application in lead-free tandem towards commercial development. • Improvement in performance of Sn wide bandgap perovskite has been achieved. • Carrier lifetime of perovskite absorber increase from 1.1 ns to 22.8 ns. • Balanced charge transfer can be achieved. • The highest PCE of 7.50% is shown for Sn perovskite with bandgap of 1.62 eV. [ABSTRACT FROM AUTHOR]

Flexible perovskite solar cells (PSCs) is being reported on different kinds of indium tin oxide (ITO)‐coated flexible substrates such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) with varying sheet resistance. High sheet resistance and low transmittance of these substrates in comparison to glass‐ITO based rigid substrate are among the major issues in achieving high power conversion efficiency (PCE), especially with large active area due to considerably low fill factor (FF) values. With a small active cell area of 0.1 cm2, it is found that sheet resistance of these substrates do not play a dominant role and the short circuit current density (JSC) depends on the transmittance of these conducting flexible substrates producing average PCE of 12.1% with PEN‐ITO (12 Ω/□) and 11.74% for PET‐ITO (49 Ω/□). When the active cell area is increased to 1 cm2, sheet resistance seems to play a major role to maintain JSC as well as FF of the flexible PSCs giving PCE of ∼10% with PEN‐ITO (12 Ω/□) in comparison to 3.4% for PET‐ITO (49 Ω/□). In contrast to PCE results, bending durability test for 1000 cycles showed that the flexible substrates with highest sheet resistance can retain maximum PCE. [ABSTRACT FROM AUTHOR]

Abstract TiO 2 has been extensively utilized as bottom electron transporting scaffold for perovskite solar cells (PSCs) but need for its high processing temperature (>450 °C) hinders its applicability for the flexible plastic substrates. Use of the low temperature processed ZnO is one of the probable solutions as electron transport layer (ETL) in PSCs owing to its high electron mobility. An amicable solution for the instability of the perovskite absorber layers fabricated on to ZnO leading resulting in to poor power conversion efficiency (PCE) and long-term stability is necessary for to harness the benefit of ZnO as ETL in PSCs. Herein, we modified the ZnO surface by spin-coating an ultrathin Nb 2 O 5 as surface passivation layer. In this work, both of the ZnO and Nb 2 O 5 were fabricated by spin coating and sintered at relatively lower temperature of 200 °C. Utilizing this Nb 2 O 5 surface passivated and low temperature processed ZnO as ETL, dramatically enhanced stability of perovskite film over 20 days under ambient condition has been clearly demonstrated. This bilayer of Nb 2 O 5 surface passivated ZnO scaffold used for fabrication of the planer heterojunction PSCs based on CH 3 NH 3 PbI 3 , led to the maximum PCE of 14.57% under simulated solar irradiation for an optimized ZnO thickness of 42 nm. Moreover, implication of the surface passivation of ZnO by Nb 2 O 5 leading to the formation of highly crystalline, stable and dense perovskite film has been probed by SEM and XRD investigations. Graphical abstract Image 1 Highlights • ZnO as an electron transport layer prepared at temperature lower than 200 °C. • ZnO surface passivation by Nb 2 O 5 solves the instability issue of perovskite films. • Nb 2 O 5 leads to the formation of highly crystalline, stable and dense perovskite film. • Perovskite films are stable over 20 days under ambient condition with best PCE of 14.58%. [ABSTRACT FROM AUTHOR]

The photoelectric properties of nontoxic Sn‐based perovskite make it a promising alternative to toxic Pb‐based perovskite. It has superior photovoltaic performance in comparison to other Pb‐free counterparts. The facile oxidation of Sn2+ to Sn4+ presents a notable obstacle in the advancement of perovskite solar cells that utilize Sn, as it adversely affects their stability and performance. The study revealed the presence of a Sn4+ concentration on both the upper and lower surfaces of the perovskite layer. This discovery led to the adoption of a bi‐interface optimization approach. A thin layer of Sn metal was inserted at the two surfaces of the perovskite layer. The implementation of this intervention yielded a significant decrease in the levels of Sn4+ and trap densities. The power conversion efficiency of the device was achieved at 14.31 % through the optimization of carrier transportation. The device exhibited operational and long‐term stability. [ABSTRACT FROM AUTHOR]

The photoelectric properties of nontoxic Sn‐based perovskite make it a promising alternative to toxic Pb‐based perovskite. It has superior photovoltaic performance in comparison to other Pb‐free counterparts. The facile oxidation of Sn2+ to Sn4+ presents a notable obstacle in the advancement of perovskite solar cells that utilize Sn, as it adversely affects their stability and performance. The study revealed the presence of a Sn4+ concentration on both the upper and lower surfaces of the perovskite layer. This discovery led to the adoption of a bi‐interface optimization approach. A thin layer of Sn metal was inserted at the two surfaces of the perovskite layer. The implementation of this intervention yielded a significant decrease in the levels of Sn4+ and trap densities. The power conversion efficiency of the device was achieved at 14.31 % through the optimization of carrier transportation. The device exhibited operational and long‐term stability. [ABSTRACT FROM AUTHOR]

CsPbI 2 Br is one of candidates of the top layer for the all perovskite tandem solar cells. However, the perovskite is prone to change the phase from α (black) to δ (yellow) type. In this research, Cs 1-x FA x PbI 2 Br perovskites were fabricated in an ambient atmosphere, and their properties immediately after the fabrication and the phase stability were investigated. The quality of the perovskite films was enhanced and the trap density was reduced after the incorporation of the FA cations. The phase stability of the Cs 1-x FA x PbI 2 Br perovskite was effectively enhanced. Consequently, the highest power conversion efficiency of 12.28% with open-circuit voltage (Voc) of 1.09 V, current intensity (Jsc) of 15.65 mA cm−2, and fill factor of 72% in the planar solar cell based on Cs 0.7 FA 0.3 PbI 2 Br perovskite is reported. The bandgap was optimized to be about 1.82 eV suitable for all perovskite tandem top layer. Most importantly, all the photovoltaic parameters of Cs 0.7 FA 0.3 PbI 2 Br perovskite solar cells showed ignorable decay after 2 months' measurement in an ambient atmosphere with the presence of air and humidity without encapsulation. • Detailed analysis to study the phase stability of CsPbI 2 Br by the introduction of FA+ cation into the crystal lattice. • A 100% internal quantum efficiency (IQE) was demonstrated in comparison to reference CsPbI 2 Br (IQE~60%) based solar cells. • Bandgap engineering of Cs x FA 1-x PbI 2 Br combined with NiO x led to a highly efficient 12.28% solar cell. • An excellent ambient air-stability of 2 months for the un-encapsulated solar cell was achieved. [ABSTRACT FROM AUTHOR]

Highlights • A novel strategy to introduce inorganic S2- on QDs surface by xanthate decomposition. • The paper aims to form QDs array and smooth surface of cross-linking QDs film. • Enhanced mobility was achieved by introduction of sulfur on PbS QDs surface. • Increased efficiency resulted from rapid charge transport in PbS QDs. Abstract A novel and facile strategy to realize selective inorganic ligand (S2−) exchange on Pb-rich surface of PbS colloidal quantum dots (QDs) has been demonstrated. This was achieved via xanthate ligand decomposition at room temperature without damaging the QDs surface. This proposed method offers an amicable solution for the limitation that inorganic-terminated colloidal QDs are restricted by the specific requirement to solvents with high dielectric constant. Furthermore, Introduction of S2− to form sulfur-crosslinking PbS QDs enables reaction force-induced QDs arrays and smooth surface morphology of the spin-coated QDs film as evidenced by atomic force microscopy. Passivation of QDs by bromide combined with sulfur led to stronger electronic coupling between adjacent QDs as compared to bromide-only passivated QDs counterparts. Bromide and sulfur hybrid-capped QDs exhibited remarkably enhanced carrier mobility from 1.66 × 10−4 cm2/V s to 5.0 × 10−1 cm2/V s as evidenced by the Hall- Effect measurement. The smooth QDs film morphology and higher charge transport contributed to the boost in the power conversion efficiency of QDs solar cells up 4.96% compared that using only CTAB passivated PbS QDs solar cells (3.04%). This controlled sulfurization approach paves a potential way for improved optoelectronic properties and devices based on QDs. [ABSTRACT FROM AUTHOR]