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Defects in perovskite films are one of the main factors that affect the efficiency and stability of halide perovskite solar cells (PSCs). Uncoordinated ions (such as Pb2+, I−) act as trap states, causing the undesirable non-radiative recombination of photogenerated carriers. The formation of Lewis acid–base adducts in perovskite directly involves the crystallization process, which can effectively passivate defects. In this work, 4-(trifluoromethyl)-1H-imidazole (THI) was introduced into the perovskite precursor solution as a passivation agent. THI is a typical amphoteric compound that exhibits a strong Lewis base property due to its lone pair electrons. It coordinates with Lewis acid Pb2+, leading to the reduction in defect density and increase in crystallinity of perovskite films. Finally, the power conversion efficiency (PCE) of PSC increased from 16.49% to 18.97% due to the simultaneous enhancement of open-circuit voltage (VOC), short circuit current density (JSC) and fill factor (FF). After 30 days of storage, the PCE of the 0.16 THI PSC was maintained at 61.9% of its initial value, which was 44.3% for the control device. The working mechanism of THI was investigated. This work provides an attractive alternative method to passivate the defects in perovskite. [ABSTRACT FROM AUTHOR]

Poly (9-vinylcarbazole) (PVK) is an attractive hole transport material for organometallic-halide perovskite solar cell (PSC) because of its excellent hole transport ability and great film-forming property. Nowadays, the PVK hole-transport-layer (HTL) based PSC suffered from low power conversion efficiency (PCE), which mainly caused by bad interface contact between PVK and perovskite film, including the energy level mismatch. Doing PVK is an effective and facial method to modify the buried interface of perovskite film. In this work, 1,1-bis [(di-4-tolylamino)phenyl]cyclohexane (TAPC) was added into PVK HTL. Experimental results show that a highest occupied molecular orbital (HOMO) level elevation was achieved after doping TAPC. Meanwhile perovskite films with increased crystallinity, reduced defect density and enhanced light absorbance were obtained. Finally, the PCE of PSCs were enhanced from 10.81% of the control device to 15.65% of PVK + 40% TAPC device. The reason that responsible for the energy level lifting, morphology improvement and performance enhancement were thoroughly investigated and analyzed. This work provides an alternative option for the dopant in PVK to improve the buried interface of perovskite film, and therefore, the performance of PSCs. • TAPC was doped in PVK to modify the buried interface of perovskite film. • The HOMO level of HTL was lifted after doping TAPC in PVK. • A reduction in defect density and an enhancement in crystallinity of perovskite film were achieved. • The PCE of PSC was enhanced from 10.98% to 15.35%. [ABSTRACT FROM AUTHOR]

A π-conjugated small molecule N, N'-bis(naphthalen-1-yl)-N, N'-bis(phenyl)benzidine (NPB) was introduced into poly(9-vinylcarbazole) (PVK) as a hole transport layer (HTL) in inverted perovskite solar cells (PSCs). The NPB doping induces a better perovskite crystal growth, resulting in perovskite with a larger grain size and less defect density. Thus, the VOC, JSC, and FF of the PSC were all enhanced. Experimental results show that it can be ascribed to the reduction of surface roughness and improved hydrophilicity of the HTL. The effect of NPB on the aggregation of PVK was also discussed. This work demonstrates the great potential of PVK as the HTL of PSCs and provides an attractive alternative for HTL to realize high-efficiency PSCs. [ABSTRACT FROM AUTHOR]

A variety of defects exist in the solution-processed polycrystalline perovskites, resulting in photovoltaic output losses and degradation. Chemical interaction is a promising way to realize the passivation of defects. Herein, cetyl pyridinium bromide (CPB) containing both pyridine units and long-chain alkyl groups was introduced in the perovskite precursor solution as a passivation agent. Experimental results show that pyridine unit in CPB formed coordination with uncoordinated Pb2+, which also interact with N–H in MAPbI 3. Meanwhile, long-chain alkyl groups in CPB had interaction with MAI and PbI 2 in MAPbI 3. Thus, trace amount of CPB in the precursor solution improved the optoelectronic properties of perovskite films and suppressed non-radiative carrier recombination in perovskite solar cell (PSC). CPB-modified perovskite films exhibit a lower trap-state density and stronger carrier migration capability. It enables the significant enhancement of PCE values of the p-i-n structured PSC from 18.27 % to 20.53 %, accompanied by the improved stability. Our work exhibits more possibility between passivating additive and PSC performance. [Display omitted] • CPB was introduced in the perovskite precursor solution as a passivation agent. • Pyridine unit in CPB formed coordination with uncoordinated Pb2+. • Long-chain alkyl groups in CPB had interaction with MAI and PbI 2 in MAPbI 3. • CPB-modified perovskite films exhibit a lower trap-state density and stronger carrier migration capability. • A significant enhancement of PCE from 18.27 % to 20.53 % was achieved. [ABSTRACT FROM AUTHOR]

Interface modification is an effective strategy to improve the performance of perovskite solar cells (PSCs). In this work, edible materials like glycerol and choline chloride were used to modify the surface of hole transport layer (HTL) NiOx. CH3NH3PbI3 (MAPbI3) film fabricated on the modified NiOx has a smoother surface and more uniform grains. It enables an improvement in short-circuit current density (JSC) of PSC from 17.77 ± 0.18 to 20.35 ± 0.36 mA cm−2, leading to an enhancement of power conversion efficiency from 13.37 to 15.25%. The work mechanism of glycerol and choline chloride modification was discussed. Our work provides an efficient and environmentally friendly choice for interface modification. [ABSTRACT FROM AUTHOR]

• DMSO was used as additive in Pb(Ac) 2 based precursor solution. • The mesophase structure delayed the crystallization of perovskite film. • The improvement of film quality of perovskite enhanced the PCE of PSCs. Organometallic halide perovskite films based on lead iodide precursor often suffered from bad repeatability and the usage of large quantities of toxic solvents due to the need for an anti-solvent washing process. Lead acetate (Pb(Ac) 2) precursor, by contrast, was more promising because of the needless of anti-solvent washing during the fabrication of perovskite films. However, the performance of perovskite solar cells (PSCs) needs to be improved. Here, we developed a simple strategy to improve the efficiency of PSCs by adding a small amount of dimethylsulfoxide (DMSO) into the precursor solution of perovskite. An increase in power conversion efficiency (PCE) of PSCs from 13.34% to 15.74% was achieved. It was found that with the addition of DMSO, a stable mesophase structure was formed, which significantly delayed the crystallization of perovskite during the spin-coating of precursor solution, resulting in more uniform and dense perovskite films. The trap intensity and charge carrier mobility of the perovskite films were estimated. The charge carrier dynamic and the recombination in the PSCs were studied. Our method provided a convenient way to improve the performance of PSCs based on Pb(Ac) 2 precursor. [ABSTRACT FROM AUTHOR]

The properties of hole transport layers (HTL) greatly affect the performance of inverted planar heterojunction perovskite solar cells (PSC). To understand the mechanisms involved, solvent treatments to HTL poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS) by DMSO, ethanol, ethanol:10 vol% DMSO, DMF and acetonitrile were performed when fabricating the PSC devices. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) results show that the crystal size of CH 3 NH 3 PbI 3 (MAPbI 3 ) increased after solvent treatment to PEDOT: PSS. MAPbI 3 film with a uniform crystal size and smooth surface was obtained when being deposited on top of PEDOT: PSS that has been modified with solvent with a strong coordination ability. In the other cases, crystal size homogeneity and surface roughness of the MAPbI 3 film was worse. The improved surface roughness and crystal size homogeneity of the MAPbI 3 film enhanced the short circuit current (J SC ), and therefore the power conversion efficiency (PCE) of PSC. It was found that both the stability of the intermediate phase MAI-DMSO-PbI 2 , which is related to the coordination ability of the solvent molecules, and the morphology of PEDOT: PSS film, influenced the morphology of the CH 3 NH 3 PbI 3 (MAPbI 3 ) film. Our findings provide the basis for better controlling the morphology of MAPbI 3 films in inverted planar heterojunction PSC. [ABSTRACT FROM AUTHOR]

Poly(9-vinylcarbazole) (PVK) is an attractive hole transport layer (HTL) for high efficiency perovskite solar cells (PSCs). But there is still some room for improvement in energy level alignment between the highest occupied molecular orbital (HOMO) of PVK and the perovskite layer. In this work, the solvent of PVK-based HTL was optimized to adjust the energy level of HTLs by changing the volume ratio of chlorobenzene (CB) in dimethylformamide (DMF). Experimental results shows that 20% is the optimal ratio of CB in DMF, based on which the HOMO level of HTL was lifted from −5.62 eV to −5.44 eV. Meanwhile, the morphology of perovskite layer with larger grain size and lower trap density was obtained. As a result, the V OC and J SC of PSCs was enhanced, leading to the increase of PCE from 15.41% to 18.27%. This work paves the way to realize high-efficiency PSCs based on PVK HTL. [Display omitted] • The solvent of PVK-based HTL was optimized to adjust the energy level of HTLs. • The HOMO level of HTL was lifted from −5.62 eV to −5.44 eV. • The V OC and J SC of PSCs was enhanced, leading to the increase of PCE from 15.41% to 18.27%. [ABSTRACT FROM AUTHOR]

The energy gap between 6,6-phenyl-C61-butyric acid methyl ester (PCBM) and silver (Ag) is disadvantage to the electron collection of perovskite solar cells (PSCs). In this work, solvent treatment is applied on the surface of PCBM by using ethanol, acetonitrile and ethanol:5 vol% acetonitrile, respectively. Experimental results showed that solvent treatment greatly enhanced the power conversion efficiency (PCE) of PSCs. After ethanol:5 vol% acetonitrile treatment, the PCE of PSC increased from 14.03 ± 0.23 % to 17.03 ± 0.13 % due to the simultaneously enhancement of V OC , J SC and FF. Electronic energy level at the surface of PCBM, electron mobility of PCBM film and the dark current density of PSCs were analysed to investigate the work mechanism of solvent treatment. • Solvent treatment was applied on the surface of PCBM. • The PCE of perovskite solar cells (PSCs) increased from 14.03 % to 17.03 %. • The shift of electronic energy level at the surface of PCBM is mainly responsible for the increase of V OC and J SC. [ABSTRACT FROM AUTHOR]

Nonradiative recombination losses caused by defects in the perovskite layer seriously affects the efficiency and stability of perovskite solar cells (PSCs). Hence, defect passivation is an effective way to improve the performance of PSCs. In this work, trichloromelamine (TCM) was used as a defects passivator by adding it into the perovskite precursor solution. The experimental results show that the power conversion efficiency (PCE) of PSC increased from 18.87 to 20.15% after the addition of TCM. What's more, the environmental stability of PSCs was also improved. The working mechanism of TCM was thoroughly investigated, which can be ascribed to the interaction between the –NH– group and uncoordinated lead ions in the perovskite. This work provides a promising strategy for achieving highly efficient and stable PSCs. [ABSTRACT FROM AUTHOR]

The morphology of perovskite light-absorption layer plays an important role in the performance of perovskite solar cells (PSCs). In this work, BiFeO3 (BFO) nanostructures were used as additive for CH3NH3PbI3 (MAPbI3) via anti-solvent method. The addition of BFO nanostructures greatly enhanced the crystallinity, grain size and film uniformity of MAPbI3. As a result, the charge carrier mobility and electron diffusion length increased, leading to the increase of the short circuit current (JSC) of PSCs. This work provides a very simple but effective approach to improve the morphology of perovskite layer for efficient PSCs. [ABSTRACT FROM AUTHOR]

• Acrylamide can neutralize the acidity of the hole-transport layer. • Acrylamide can optimize the quality of the FASnI 3 perovskite film. • The efficiency of FASnI 3 perovskite solar cells is increased by almost 46 %. The quality of the hole transport layer (HTL) is crucial for the overall efficiency of the perovskite solar cells. Although poly(3,4-ethylenedioxythiophene)/poly(styrene sulfonic acid) (PEDOT:PSS) has been widely used as HTL for the perovskite solar cells, there is still room for further improvement of PEDOT:PSS by optimizing its energy level matching and the hole transfer efficiency. Based on the present issues of applying PEDOT:PSS as HTL in tin-based perovskite solar cells, the Lewis alkali acrylamide (AM), which contains both carbon-carbon double bond and the electrophilic amide group, is applied as the dopant in PEDOT:PSS solution. By analyzing the surface morphology and the crystal structure, it is revealed that AM can effectively improve both the quality and crystallinity of the formamidinium tin tri-iodide (FASnI 3) perovskite film, with the defects of the perovskite film greatly suppressed. The grain size of the modified FASnI 3 perovskite is observed to increase with the surface roughness reducing at the same time, along with the charge recombination resistance of the FASnI 3 perovskite film increasing. As a result, the modified devices have a higher short-circuit current, fill factor as well as power conversion efficiency. The characterization of the surface contact angle indicates that a more hydrophobic surface is formed as for the FASnI 3 perovskite film, which could efficiently retard the ambient vapor penetrating into the perovskite film. [ABSTRACT FROM AUTHOR]

• Poly(α-methylstyrene) is used as additive to modify the property of the antisolvent. • Poly(α-methylstyrene) can significantly influence the surface morphology of the perovskite layer. • The enhancement of PCE by almost 70% is achieved based on FASnI 3 perovskite solar cells. Surface quality of the perovskite layer plays an important role in the determination of the device performance. This study presents an effective method to optimize the surface morphology for the lead-free formamidinium tin iodide (FASnI 3) perovskite solar cells. Poly(α-methylstyrene) (PAMS) was applied as polymer additive into the diethyl ether at different blend concentration. The addition of PAMS can apparently reduce the pinholes at the surface of the FASnI 3 film without ruining the interior crystallinity of the bulk FASnI 3 layer. Therefore the non-radiative carrier traps can be effectively suppressed. The surface of the FAsnI 3 film becomes more hydrophobic which facilitates the consequent spin-coating of the acceptor material solution. The modification of FASnI 3 film's wettability is favorable of the photo-induced carriers' extraction and transportation. As a result, the power conversion efficiency of the PAMS-modified devices is greatly improved. [ABSTRACT FROM AUTHOR]

The process of the antisolvent rinsing plays an important role during the formation of the perovskite crystals. Since the function of the single-component antisolvent may be limited, a reducing agent named acetaldoxime (AO) was applied as the additive for the antisolvent. The analysis of both the surface morphology and the crystal structure indicates that AO can effectively improve the quality of the FASnI 3 perovskite film. The defects of the perovskite film can be greatly suppressed. Moreover, due to the increase of the crystal grain size with the surface roughness reducing at the same time, the charge recombination resistance of the FASnI 3 perovskite film increases. Therefore, the devices modified by AO have higher short-circuit current, fill factor as well as power conversion efficiency. At the same time, the surface of the FASnI 3 perovskite film becomes more hydrophobic, which benefits impeding the permeation of the ambient vapor into the perovskite film. The results of lifetime testing show that the stability of the devices is greatly improved. [Display omitted] • Acetaldoxime is first used as the additive in the antisolvent to adjust the crystallization process of the perovskite. • The addition of acetaldoxime can significantly optimize the morphology and crystallinity of the FASnI 3 perovskite film. • PCE of FASnI 3 perovskite solar cells is increased by almost 50%. [ABSTRACT FROM AUTHOR]

High-quality PEDOT:PSS layer plays an important role in achieving efficient FASnI 3 perovskite solar cells. To overcome the defects of the conventional PEDOT:PSS layer, edetate disodium (EDTA-2Na) was applied as the dopant into the PEDOT:PSS solution to modify the film quality. By characterizing the surface morphology and the analysis of the bulk crystallization, it reveals that the incorporation of EDTA-2Na can efficiently optimize the surface morphology, surface energy state and the grain size of the perovskite crystals. Therefore the open-circuit voltage of the perovskite devices can be improved, which as a result leads to the enhancement of the overall device performance as long as the doping concentration of EDTA-2Na was optimized. • Edetate disodium was first used as the dopant to modify the quality of the PEDOT:PSS layer. • Both grain size and surface morphology of the FASnI 3 perovskite were optimized after edetate disodium was added. • The device PCE was increased by more than 30% as for FASnI 3 -based perovskite solar cells. [ABSTRACT FROM AUTHOR]

Nickel oxide (NiOx) has been widely used as a hole transport layer (HTL) of p-i-n type perovskite solar cells (PSCs) because of its many unique properties. However, the poor contact between NiOx and perovskite is disadvantage to the fabrication of high-quality perovskite film, which has bad effect on the open-circuit voltage (V OC), short-circuit current density (J SC) and fill factor (FF) of PSCs. In this report, poly(vinyl alcohol) (PVA) was used as a modifier on the surface of NiOx. Experimental results showed that after PVA modification the PCE of PSCs increased significantly from 16.79% to 19.17% due to the increase of J SC and FF. The MAPbI 3 film on top of the PVA modified NiOx showed larger crystal size, less defect intensity and higher hole mobility. The work mechanism of PVA modification was investigated. This work provides an effective and simple method to improve the performance of PSCs. • PVA modification on NiOx increased the PCE of PSCs from 16.79% to 19.17%. • The film quality of MAPbI 3 was improved after PVA modification. • The wettability of MAPbI 3 precursor solution on NiOx was enhanced. [ABSTRACT FROM AUTHOR]