In vacuo XPS investigation of Cu In,Ga Se2 surface after RbF post deposition treatment

Latest record efficiencies of Cu In,Ga Se2 CIGSe solar cells were achieved by means of a rubidium fluoride RbF post deposition treatment PDT . To understand the effect of the RbF PDT on the surface chemistry of CIGSe and its interaction with sodium that is generally present in the CIGSe absorber, we performed an X ray photoelectron spectroscopy XPS study on CIGSe thin films as deposited by a three stage co evaporation process and after the consecutive RbF PDT. The sample transfer from the deposition to the XPS analysis chamber was performed via an ultra high vacuum transfer system. This allows to minimize air exposure, avoiding oxide formation on the CIGSe surface, especially for alkali treated absorbers. Beside an expected reduction of Cu and Ga content at the surface of RbF treated CIGSe films, we find that Rb penetrates the CIGSe and, contrary to fluorine, it is not completely removed by subsequent ammonia etching. The remaining Rb contribution at 110.0 amp; 8239;eV binding energy, which appears after the RbF PDT is similar to the one detected on a co evaporated RbInSe2 reference sample and together with a new Se 3d contribution may hence belong to an Rb In Se secondary phase on the CIGSe surface. In addition, Na is driven towards the surface of the CIGSe absorber as a direct result of the RbF PDT. This proves the ion exchange mechanism in the absence of moisture and air oxygen between heavy Rb atoms incorporated via PDT and lighter Na atoms supplied by the glass substrate. A remaining XPS signal of Na 1 amp; 8239;s is observed after etching the vacuum transferred RbF CIGSe sample, indicating that Rb and or F are not as much a driving force for Na as oxygen usually i

A post deposition annealing approach for organic residue control in TiO2 and its impact on Sb2Se3 TiO2 device performance

We report a systematic investigation on the influence of two step post deposition treatments PDTs on TiO2 buffer layers deposited by ultrasonic spray pyrolysis USP for emerging Sb2Se3 photovoltaics. Air annealing is a typical method for recrystallizing chemically deposited TiO2 films. However, organic residues such as carbon species from a precursor solution based on titanium tetraisopropoxide and acetylacetone may still remain on the TiO2 surface, therefore requiring an additional annealing step. We demonstrate that vacuum annealing can be a suitable technological approach to decrease the concentration of carbon species in TiO2 films. Vacuum annealing was performed at temperatures at 160 450 C prior to the 450 C air annealing step. It was found that vacuum annealing at 160 C followed by subsequent air annealing led to better device performance. This was explained by achieving an optimal balance between the removal of carbon content during vacuum annealing and the active recrystallization of TiO2 during air annealing. The decrease of carbon concentration by employing the two step approach was supported by changes in the lattice parameters of TiO2 and proven by X ray photoelectron spectroscopy XPS . The given study provides experimental evidence on how nanoscale carbon species in the TiO2 heterojunction partner layer of a Sb2Se3 solar cell can affect the device s performance. By this approach, we generate complementary insights on how the quality of the main interface has an impact and can take a key role despite the optimized Sb2Se3 grain structure and orientatio

ZnO NiO heterostructures with enhanced photocatalytic activity obtained by ultrasonic spraying of a NiO shell onto ZnO nanorods

Degradation of organic pollutants such as methylene blue MB from water resources is currently of particular interest. Employment of a heterojunction device with optimized layer properties and proper interface engineering can enhance the photocatalytic performance by taking advantage of efficient charge separation. In this work, we develop an efficient photocatalytic system for the MB degradation based on ZnO nanorod ZnONR NiO core shell heterostructure with an optimized chemical and electronic structure for achieving record MB degradation efficiency of 70 . ZnONR were grown by hydrothermal technique, whereas homogeneous crystalline NiO thin films were prepared by a robust and easy for up scaling method of ultrasonic spray pyrolysis USP . The optimum preparation conditions of photocatalytically efficient ZnONR NiO heterostructures imply NiO film deposition from two USP cycles at 500 C followed by air annealing heterostructures at 600 C. The photocatalytic performance of ZnONR NiO core shell structure was investigated in comparison to counterpart layers and ZnO NiO bilayer system. Chemical composition and band alignment at the ZnONR NiO interface were investigated by X ray photoelectron spectroscopy, Kelvin probe and photoelectron yield spectroscopy. Current transport studies indicated the presence of built in electric field at the n ZnO p NiO heterointerface responsible for the enhanced photocatalytic activity and based on this the degradation mechanism of MB is discusse

Host, Suppressor, and Promoter The Roles of Ni and Fe on Oxygen Evolution Reaction Activity and Stability of NiFe Alloy Thin Films in Alkaline Media

Understanding the oxygen evolution reaction OER activity and stability of the NiFe based materials is important for achieving low cost and highly efficient electrocatalysts for practical water splitting. Here, we report the roles of Ni and Fe on the OER activity and stability of metallic NiFe and pure Ni thin films in alkaline media. Our results support that Ni OH 2 NiOOH does not contribute to the OER directly, but it serves as an ideal host for Fe incorporation, which is essential for obtaining high OER activity. Furthermore, the availability of Fe in the electrolyte is found to be important and necessary for both NiFe and pure Ni thin films to maintain an enhanced OER performance, while the presence of Ni is detrimental to the OER kinetics. The impacts of Fe and Ni species present in KOH on the OER activity are consistent with the dissolution re deposition mechanism we proposed. Stability studies show that the OER activity will degrade under prolonged continuous operation. Satisfactory stability can, however, be achieved with intermittent OER operation, in which the electrocatalyst is cycled between degraded and recovered states. Accordingly, two important ranges, that is, the recovery range and the degradation range, are proposed. Compared to the intermittent OER operation, prolonged continuous OER operation i.e., in the degradation range generates a higher NiOOH content in the electrocatalyst, which is likely related to the OER deactivation. If the electrode works in the recovery range for a certain period, that is, at a sufficiently low reduction potential, where Ni3 is reduced to Ni2 , the OER activity can be maintained and even improved if Fe is also present in the electrolyt

Combinative solution processing and Li doping approach to develop p type NiO thin films with enchanced electrical properties

The deposition of nickel oxide NiOx thin film from an acetylacetonate source using many solution based techniques has been avoided owing to its poor solubility in alcohol solvents. From this perspective, this work provides a systematic investigation of the development of NiOx thin film, using a combinative approach of ultrasonic spray pyrolysis USP and Li dopant for the synthesis and optimization of structural and optoelectronic properties of the films. An in depth comparative analysis of nickel acetylacetonate based precursor, employing acetonitrile and methanol as solvents, is provided. It is demonstrated that USP from acetylacetonate precursor yielded uniform, well compact, and transparent films, with polycrystalline cubic NiOx crystal structures. By screening the deposition temperature in the range of 300 450 C, a temperature of 400 C was identified as an optimal processing temperature leading to uniform, compact, highly transparent, and p type conductive films. At optimized deposition conditions 400 C , lithium doped NiOx Li NiOx thin film was deposited. The shift of the main 200 XRD peak position from 43.48 0 Li NiOx to 43.56 60 Li NiOx indicated Li incorporation into the NiOx lattice. An X ray photoelectron spectroscopy XPS study was employed to unravel the incorporation of Li into the deposited Li NiOx thin films. With the deconvolution of the Ni 2p core level for the as deposited 0, 60 Li NiOx films, the intensity of Ni3 related peak was found to increase slightly with Li doping. Furthermore, all the deposited Li NiOx thin films showed p type conductivity behavior, and the resistivity was reduced from 104 amp; 937;cm 0 Li NiOx to 102 amp; 937;cm 60 Li NiOx . Based on these results, the deposited NiOx and Li NiOx thin films suggested that USP deposited Li NiOx is highly suitable for application in inverted structure solar cells as the hole transport laye

Disentangling the effect of the hole-transporting layer, the bottom, and the top device on the fill factor in monolithic CIGSe-perovskite tandem solar cells by using spectroscopic and imaging tools

We present monolithic copper–indium–gallium–diselenide (Cu(In,Ga)Se _2 , CIGSe)-perovskite tandem solar cells with air- or N _2 -transferred NiO _x :Cu with or without self-assembled monolayer (SAM) as a hole-transporting layer (HTL). A champion efficiency of 23.2%, open-circuit voltage (V $_\mathrm{oc}$ ) of 1.69 V, and a fill factor (FF) of 78.3% are achieved for the tandem with N _2 -transferred NiO _x :Cu + SAM. The samples with air-transferred NiO _x :Cu + SAM have V $_\mathrm{oc}$ and FF losses, while those without SAM are heavily shunted. We find via x-ray and UV photoelectron spectroscopy that the air exposure leads to non-negligible loss in the Ni ^2+ species and changes in the NiO _x :Cu’s work function and valence band maxima, both of which can negatively impact the V $_\mathrm{oc}$ and the FF of the tandems. Furthermore, by performing dark lock-in thermography, photoluminescence (PL), and scanning electron microscopy studies, we are able to detect various morphological defects in the tandems with poor performance, such as ohmic shunts originating from defects in the bottom CIGSe cell, or from cracking/delaminating of the perovskite top cell. Finally, by correlating the detected shunts in the tandems with PL-probed bottom device, we can conclude that not all defects in the bottom device induce ohmic shunts in the tandems since the NiO _x :Cu + SAM HTL bi-layer can decouple the growth of the top device from the rough, defect-rich and defect-tolerant bottom device and enable high-performing devices

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

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

Impact of RbF post deposition treatment on CdS CIGSe and Zn O,S CIGSe interfaces e A comparative HAXPES study

In conventional Cu In,Ga Se2 CIGSe solar cells a chemical bath deposited CdS thin film is used as a buffer layer. However, it is desired to replace CdS due to the toxicity of cadmium and the rather narrow bandgap energy of CdS. Zn O,S is considered to be one of the most attractive candidates as an alternative, non toxic buffer layer with a larger bandgap. This paper aims to compare the properties of the CdS CIGSe and the Zn O,S CIGSe interfaces depending on the absorber composition and the application of an RbF post deposition treatment PDT . Synchrotron based hard X ray photoelectron spectroscopy revealed a strong correlation of Cd diffusion and concentration of VCu in CIGSe before the PDT. Additionally, the RbF PDT enhanced the Cd diffusion into the CIGSe. On the other hand, it was found that Zn atoms are not as easily incorporated into the CIGSe as Cd atoms. As a result, we consider the formation of donor like ZnCu defects at the interface to be less likely than the formation of CdCu defects. Moreover, we observed that the Zn O,S CIGSe interface is less sensitive to changes of the CIGSe composition and to the RbF PDT compared to the CdS CIGSe interfac

Depth resolved analysis of the effect of RbF post deposition treatment on CIGSe with two different Cu concentrations

Photovoltaic devices based on Cu In,Ga Se2 CIGSe absorbers are among the most attractive non Si alternatives. The key to their steadily increasing efficiency is a post deposition treatment PDT with alkali salts. For co evaporated CIGSe, a RbF PDT was demonstrated as the most efficient, however, the mechanism of the RbF influence on the CIGSe absorber is not completely understood. Here, we focus on the impact of RbF on the surface of co evaporated CIGSe absorbers in dependence on their bulk composition. Surface as well as bulk sensitive methods with overlapping information depths are used to examine an overall depth profile of RbF free and RbF treated CIGSe samples with different Cu contents. We show a gradual depletion of copper towards the surface for the as deposited CIGSe absorber layers. The following RbF PDT sharpens this effect especially for the sample grown with the overall lower Cu content. Under the Cu depleted surface layer, the composition of the CIGSe gradually changes until it reaches the respective bulk composition. As a result of the RbF PDT, Ga diffuses towards the surface and Rb gets incorporated at the surface where GaF3 and RbInSe2 secondary phases are formed, respectively. A higher Cu content leads to less surface oriented Ga diffusion, less Rb incorporation and to a thinner RbInSe2 layer. A thinner RbInSe2 barrier layer, in turn, maintains the gain in open circuit voltage and prevents the fill factor loss of the CIGSe devic