Bulk Defect Density Research Articles

Elucidating the origin of external quantum efficiency losses in cuprous oxide solar cells through defect analysis

Heterojunction Cu2O solar cells are an important class of Earth-abundant photovoltaics that can be synthesized by a variety of techniques, including electrochemical deposition (ECD) and thermal oxidation (TO). The latter gives the most efficient solar cells of up to 8.1% reported in the literature, but is limited by low external quantum efficiencies (EQE) in the long wavelength range (490–600 nm). By contrast, ECD Cu2O gives higher short wavelength EQEs of up to 90%. We elucidate the cause of this difference by characterizing and comparing ECD and TO films using impedance spectroscopy and fitting with a lumped circuit model to determine the trap density, followed by simulations. The data indicates that TO Cu2O has a higher density of interface defects, located approximately 0.5 eV above the valence band maximum (NV), and lower bulk defect density thus explaining the lower short wavelength EQEs and higher long wavelength EQEs. This work shows that a route to further efficiency increases of TO Cu2O is to reduce the density of interface defect states.

Investigation of thin-film p-BaSi2/n-CdS heterostructure towards semiconducting silicide based high efficiency solar cell

In this article, semiconducting Barium Silicide (BaSi2) absorber based novel heterostructure thin-film solar cell (TFSC) has been studied in details. The solar cell has been numerically simulated and intensely analyzed by Solar cell Capacitance Simulator (SCAPS). Layer thickness was varied from 100 to 3000 nm for p+-BaSi2 absorber, 20 to 200 nm for both n-CdS buffer, and n+-SnO2:F window layers to optimize the device. Hitherwards, the impurities concentration for acceptor (NA) and donor (ND) ions was optimized for each layer through ample variation. The influence of single-donor and acceptor type bulk defect densities has been investigated thoroughly in p+-BaSi2 and n-CdS materials, respectively. An efficiency >30% is achievable ideally with a 2 μm thick BaSi2 absorber without incorporating defects whereas it reduces to 26.32% with only 1.2 μm thick absorber including certain amount of defects. Cell thermal stability and alteration of cell parameters were studied under cell operating temperature from to Finally, the effect of series (Rs) and shunt (Rsh) resistances on proposed cell has been investigated meticulously. This newly designed solar cell structure proclaims the chance of fabricating a resourceful, low cost, and highly efficient TFSC near future.

Bulk defects induced coercivity modulation of Co thin film based on a Ta/Bi double buffer layer

This paper reports the effect of Ta/Bi double buffer layer on the magnetic properties of Co thin film. By inserting a Bi layer into the Ta/Co interface of Ta/Co/Ru, the coercive field is increased by about 6 times. Moreover, a further increase of coercivity is observed for the Ta/Bi/Co/Ru film after 450 ℃ annealing. X-ray photoelectron spectroscopy (XPS) reveals that the Bi atoms diffuse to film surface through the cobalt layer. Positron annihilation spectroscopy (PAS) indicates that the diffusion of Bi atoms promotes the formation of vacancies, which may increase the density of bulk defects in the film and enhance the pinning strength of the magnetic domains of Co. Besides, high-resolution transmission electron microscopy (HRTEM) results confirm the better crystallization of Co layer with a uniform orientation due to the Bi diffusion, which increases the energy barrier for nucleation and movement of the reversal domain. These two reasons lead to the increase of coercivity simultaneously. This finding provides a feasible avenue for the tunable coercive field by the defect engineering.

Performance enhancement of CIGS-based solar cells by incorporating an ultrathin BaSi2 BSF layer

Conventional copper indium gallium diselenide (CIGS)-based solar cells offer higher efficiency than other second-generation technologies such as hydrogenated amorphous silicon (a-Si:H)- or cadmium telluride (CdTe)-based solar cells, but higher manufacturing cost due to the use of the rare metals indium and gallium. The purpose of the work presented herein is to improve the efficiency of such devices by using cheaper materials. Accordingly, a back-surface field layer made of low-cost and widely available barium silicide (BaSi2) with a thickness of 0.3 µm is introduced for the first time into the basic CIGS solar cell structure consisting of Al/ZnO/CdS/CIGS/Mo, resulting in the alternative structure of Al/FTO/CdS/CIGS/BaSi2/Mo, with fluorine-doped tin oxide (FTO) as the window layer. One-dimensional simulations of the solar cell capacitance are employed to study the photovoltaic parameters such as the power conversion efficiency, short-circuit current density, open-circuit voltage, fill factor, and quantum efficiency of the devices. The thickness of the CIGS absorber layer is varied from 0.1 to 3 µm to optimize the device. Besides, the effects of the acceptor ion and bulk defect densities in the CIGS absorber layer, cell resistances, and operating temperature on the overall performance are also investigated. The proposed structure offers an efficiency of 26.24% with a thin CIGS layer of only 0.8 µm. In addition to reduced CIGS thickness and cost, the presented approach results in CIGS solar cells with enhanced performance compared with previously reported conventional designs.

Numerical simulation of charge transport layer free perovskite solar cell using metal work function shifted contacts

Perovskite solar cells (PSCs) are one of the fastest emerging photovoltaic (PV) technology at the research level. To achieve higher conversion efficiencies from PSCs, a perovskite absorber layer is stacked between two charge transport layers (CTLs) such as electron and hole transport layers. However, fabrication of defect-free multi-layered PSC is a challenging task, and the presence of CTL and their corresponding interfaces with perovskite enhances the recombination, hysteresis and led to poor stability. Here, in this work, CTL free (i.e., electron and hole transport layer free) PSC is simulated using metal work function shifted contacts. The device presented in this work is free from transport layers and the collection process is with the help of an electric field across the perovskite layer. The electric field is created by using two metals of different work function, i.e., 4.35 eV and 5.25 eV (can be realized using self-assembled monolayers technique) used as cathode and anode respectively. Simulated CTL free PSC exhibits JSC = 17.8 mA cm−2, VOC = 712 mV, FF = 68.5% and PCE = 8.7% with 250 nm thick perovskite absorber layer having bulk defect density of 2.5 × 1013 cm−3. Further, a comprehensive study is done in terms of front electrode work function (FEW), front electrode transparency, perovskite thickness and bulk defect density to understand the impact of these parameters on the performance of the device. To understand the behavior of the device, the energy band diagram profile is examined. Reported results show that higher metal work function difference between front and back electrode, higher transparency, and thick perovskite layer with low defect density results in better PV effect in CTL free PSC. Optimized CTL free PSC device delivers JSC = 19.9 mA cm−2, VOC = 726 mV, FF = 66.8% and PCE = 9.7%. The design simulated in this work opens up a new window for next-generation interface defect and hysteresis-free PSC.

Resistance fluctuation spectroscopy of thin films of 3D topological insulator BiSbTeSe1.6

Despite several years of studies, the origin of slow-kinetics of charge-carriers at the surface-states of strong topological insulators remains abstruse. In this article, we report on studies of charge dynamics of thin films of the 3-dimensional strong topological insulator material BiSbTeSe1.6 grown by pulsed laser deposition (PLD). The bulk of the films was insulating, making them suitable for transport studies of topological surface-states. Despite being disordered and granular, the films show definite signatures of the presence of topological surface-states with electronic transport coherence lengths comparable to those of high-quality grown films grown by molecular beam epitaxy (MBE). At high temperatures, the resistance fluctuations in these films were found to be dominated by trapping-detrapping of charge carriers from multiple defect-levels of the bulk. At low temperatures, fluctuations in the resistance of surface-states, arising due to the coupling of surface transport with defect dynamics in bulk, determine the noise. We thus confirm that the measured low-frequency fluctuations in these films, over the entire temperature range of 20 mK–300 K, are determined primarily by bulk defect density. The magnitude of noise was comparable to that measured on bulk-exfoliated films but was slightly higher than that in MBE grown films. Our studies establish PLD as a viable route to develop high-quality topological insulator materials.

Activation of Small Organic Molecules on Ti2+-Rich TiO2 Surfaces: Deoxygenation vs. C–C Coupling

Abstract Rutile TiO2 is an important model system for understanding the adsorption and conversion of molecules on transition metal oxide catalysts. In the last decades, point defects, such as oxygen vacancies and Ti3+ interstitials, exhibited an important influence on the reaction of oxygen and oxygen-containing molecules on titania surfaces. In brief, partially reduced TiO2 containing a significant amount of Ti3+ is often more active for the conversion of such molecules. In this study, we investigate an even higher reduced surface prepared by argon ion bombardment of a rutile TiO2 (110) single crystal. By X-ray photoelectron spectroscopy we show that, besides Ti4+, this surface is almost equally dominated by Ti3+ and Ti2+. To probe the reactivity of these highly reduced surfaces, we have adsorbed two different classes of oxygen-containing molecules and utilized temperature programmed reaction spectroscopy to investigate the conversion. While alcohols (in this case methanol) already show a defect-dependent partial conversion in a deoxygenation reaction on the (stochiometric or slightly reduced) rutile TiO2 (110) surface, ketones (e.g. acetone) are usually not converted on the rutile TiO2 (110) surface independent on the bulk defect density. Here, we present a nearly full conversion for both molecules via deoxygenation reactions and reductive C–C coupling, forming different hydrocarbons at different temperatures between 375 K and 640 K on the sputtered Ti2+ rich surface.

Dependence of electrical properties on sulfur distribution in atomic-layer-deposited HfO2 thin film on an InP substrate

S passivation of a HfO 2 film on an InP substrate is demonstrated using annealing in H 2 S ambient either before or after ALD of the HfO 2 film. We examined the resulting distribution and chemical state of the incorporated S both in the HfO 2 film and at its interface with the InP substrate using secondary ion mass spectroscopy and X-ray absorption spectroscopy. Annealing in H 2 S ambient before ALD of HfO 2 resulted in accumulation of S at the interface in the sulfide (S 2− ) phase (due to lack of oxygen), which effectively suppressed interfacial reactions during ALD and passivated interfacial defect states. On the other hand, annealing in H 2 S ambient after ALD of the HfO 2 film induced a sulfate (S 6+ ) phase in the film due to the abundant oxygen in the film, as well as a sulfide (S 2− ) phase at the interface. This improved the charge trapping behavior by decreasing the bulk defect density in the HfO 2 film. • S passivation of HfO 2 film on InP substrate was demonstrated via annealing in H 2 S ambient before and after ALD of HfO 2 film. • S was present in the HfO 2 film and interface with InP substrate in the form of sulfide and sulfate, respectively. • Post-treatment resulted in more S concentration in the HfO 2 film compared to pre-treatment. • S passivation suppressed the interfacial reactions and passivated the defect states in the film and interface.

Air-Stable and Oriented Mixed Lead Halide Perovskite (FA/MA) by the One-Step Deposition Method Using Zinc Iodide and an Alkylammonium Additive.

We present a one-step method to produce air-stable, large-grain mixed cationic lead perovskite films and powders under ambient conditions. The introduction of 2.5 % of Zn(II), confirmed by X-ray diffraction (XRD), results in stable thin films which show the same absorption and crystal structure after 2 weeks of storage under ambient conditions. Next to prolonged stability, the introduction of Zn(II) affects photophysical properties, reducing the bulk defect density, enhancing the photoluminescence (PL), and extending the charge carrier lifetime. Furthermore, 3-chloropropylamine hydrochloride is applied as the film-forming agent. The presence of this amine hydrochloride additive results in highly oriented and large crystal domains showing an ulterior improvement of PL intensity and lifetime. The material can also be prepared as black precursor powder by a solid–solid reaction under ambient conditions and can be pressed into a perovskite pellet. The prolonged stability and the easy fabrication in air makes this material suitable for large-scale, low-cost processing for optoelectronic applications.

Numerical simulation and optimization of Si/BaSi2 heterojunction and BaSi2 homojunction solar cells

High light absorption material BaSi2 based heterojunction and homojunctin solar cells were simulated with the program AMPS (analysis of microelectronic and photonic structures)-1D in order to thoroughly understand the mechanism for further improvement in conversion efficiency. Simulation results demonstrated that p+-Si/n-BaSi2 heterojunction solar cells exhibited superior photoelectric performances as compared with n+-Si/p-BaSi2 solar cells. A high conversion efficiency up to of 22.7% were achieved by p+-Si (100 nm, NA = 5 × 1019 cm−3)/n-BaSi2 (2000 nm, ND = 1 × 1018 cm−3) heterojunction solar cell. For BaSi2/BaSi2 homojunction solar cells, the window layer should be designed as thin with large scale uniformity and high quality in achieving high efficiency. Both n+-BaSi2 (5 nm, ND = 5 × 1019 cm−3)/p-BaSi2 (2000 nm, NA = 1 × 1017 cm−3) homojunction and p+-BaSi2 (5 nm, NA = 5 × 1019 cm−3)/n-BaSi2 (2000 nm, ND = 1 × 1017 cm−3) homojunction solar cells gave out a high conversion efficiency of 22.5%. Both donor-like defects in p-BaSi2 and acceptor like defects in n-BaSi2 light absorption layers were identified to significantly influence the solar cell performance that all parameters deteriorated severely under high bulk defect density. Moreover, p+-Si/n-BaSi2 solar cell was more sensitive to high level interface trap defects on account of the sharp dropping down of Eff under high interface trap density over 5 × 1012 cm−2. This work provided insight essential guidance for device design and optimization in achieving high efficiency silicide solar cell with low cost.

Bulk Defect Dependence of Low-Temperature Partial Oxidation of Methanol and High-Temperature Hydrocarbon Formation on Rutile TiO2 (110)

Titanium dioxide (TiO2) is among the most studied model (photo)catalyst materials. The influence of surface point defects, like oxygen vacancies and particularly bulk defects such as Ti3+ interstitials, is usually underestimated or even ignored. We present a systematic study under well-defined UHV conditions illustrating the importance of such defects for the thermal reaction of methanol at the rutile TiO2 (110) single crystal surface by using temperature-programmed reaction spectroscopy (TPRS) and Fourier-transform infrared reflection–absorption spectroscopy (FT-IRRAS). It will be shown that the population of different reaction pathways, namely, the partial oxidation of methanol to formaldehyde and the deoxygenation forming hydrocarbons, especially methane, depends on the bulk defect density and the presence or absence of oxygen adsorbates. While at elevated temperatures molecular desorption is pronounced for the less defective substrates, for higher reduction grades the high-temperature deoxygenation ch...

Improving the photovoltaic effect by resistive switching

The mismatch between band structures of a light-absorptive layer and hole or electron transport layers will significantly deteriorate the performance of photovoltaic devices, which is generally alleviated by inserting a mitigating layer. In this report, we propose an alternative strategy to improve the efficiency by using resistive switching, which may decrease defect density in bulk and the lower barrier height at the interface due to the migration of defects to the interface under a certain electric field. By using a BiFeO3 film as a model light harvesting layer, a TiO2 mesoporous layer as an electron transport layer, and NiOx as a hole transport layer, bipolar resistive switching behavior has been observed. By setting the device in the low resistance state under certain applied voltages, performance has been significantly improved. Compared with the virgin device, the highest short-circuit current Jsc increases 2.3 times from 2.38 to 5.66 μA cm−2 and open-circuit voltage Voc increases 1.35 times from 0.39 to 0.525 V.

Interface-Dependent Radiative and Nonradiative Recombination in Perovskite Solar Cells

Interfacial engineering has shown to play an essential role to optimize recombination losses in perovskite solar cells; however, an in-depth understanding of the various loss mechanisms is still underway. Herein, we study the charge transfer process and reveal the primary recombination mechanism at inorganic electron-transporting contacts such as TiO2 and its modified organic rivals. The modifiers are chemically ([6,6]-phenyl C61 butyric acid, PC60BA) or physically ([6,6]-phenyl C61 butyric acid methyl ester, PC60BM and C60) attached fullerene to the TiO2 surface to passivate the density of surface states. We do not observe any change in morphology, crystallinity, and bulk defect density of halide perovskite (CH3NH3PbI3 in this case) upon interface modification. However, we observe compelling results via photoluminescence and electroluminescence studies that the recombination dynamics at both time scales (slow and fast) are largely influenced by the choice of the selective contact. We note a strong correl...

Classical modelling of grain size and boundary effects in polycrystalline perovskite solar cells

A theoretical approach based on the Matthiessen rule for scattering lifetime is presented to formulate the effective characteristics of polycrystalline solar cells. Application of this method to Perovskite solar cells obtains polycrystalline bulk defect density for diverse grain sizes along with the determination of surface recombination velocity at grain boundaries. Unlike previous works on Silicon based solar cells that use an independently weighted average equation for extracting mobility, we introduce a variation of Drude-Smith model for calculating the mobility from carrier lifetime and defect density. In agreement with the experiments, introduced method reveals sub-picosecond background scattering times associated with phonon-lattice vibrations. Obtained carrier diffusion length spans over multi-micron to multi-millimeter scale for grain sizes ranging from 100 nm to 1 mm. Calculated monomolecular recombination lifetimes explains elevated Photoluminescence Yield and peak position in larger grain sizes. Presented method is verified by feeding extracted parameters into Drift-Diffusion equations and fitting with reported experimental photovoltaic conversion efficiency data. Finally, through employing a Gaussian distribution for grain sizes, we also study the reduction of device efficiency caused by non-uniform grain size distribution as a more realistic case.

Guidelines for Optimization of the Absorber Layer Energy Gap for High Efficiency Cu(In,Ga)Se<sub>2</sub> Solar Cells

This work investigates in-depth the effects of variation of the compositional ratio of the absorber layer in Cu(In,Ga)Se2 (CIGS) thin-film solar cells. Electrical simulations were carried out in order to propose the most suitable gallium double-grading profile for the high efficiency devices. To keep the model as close as possible to the real behavior of the thin film solar cell a trap model was implemented to describe the bulk defects in the absorber layer. The performance of a solar cell with a standard CIGS layer thickness (2 μm) exhibits a strong dependence on the front grading height (decreasing band gap toward the middle of the CIGS layer). An absolute gain in the efficiency (higher than 1%) is observed by a front grading height of 0.22. Moreover, simulation results show that the position of the plateau (the region characterized by the minimum band gap) should be accurately positioned at a compositional ratio of 20% Ga and 80% In, which corresponds to the region where a lower bulk defect density is expected. The developed model demonstrates that the length of the plateau is not playing a relevant role, causing just a slight change in the solar cell performances. Devices with different absorber layer thicknesses were simulated. The highest efficiency is obtained for a CIGS thin film with thicknesses between 0.8 and 1.1 μm.

Microstructural characterization and in-situ sulfur isotopic analysis of silver-bearing sphalerite from the Edmond hydrothermal field, Central Indian Ridge

A close Zn-Ag association has been noted recently in several polymetallic sulfide ore deposits from the Indian Ocean. However, the role of nanotextural controls on “invisible” silver distribution within sphalerite (a significant Ag-carrier) is still not well understood. In this study, typical Zn-sulfide samples from the Edmond vent field (Central Indian Ridge) can be roughly classified into three different groups based on their chemical compositions and mineral textures. Among them, sulfosalt-bearing, Fe-poor zinc sulfides in sulfate-dominant outer chimney walls usually contain higher contents of Ag, Cu and Pb (up to wt% levels) than Fe-rich, massive to disseminated sphalerite in Zn-(Fe)-rich chimney fragments coated by silicified crusts. Such sphalerite is represented by colloform/botryoidal aggregates of optically anisotropic ZnS with a strongly disordered structure or hexagonal habit, which are actually formed by coalescence and agglomeration of colloidal nanocrystalline particles. Using high-resolution transmission electron microscopy (HRTEM) and in-situ micro-XRD techniques, we have investigated the ultrastructure and crystal-chemistry of the {1 1 1} twin boundaries and wurtzite-type stacking faults that occur in Ag-rich, colloform or porous dendritic sphalerite. Submicroscopic electrum and Ag nanoparticles appear to nucleate on the micro-/nano-pore walls as cavity-fillings, or occur along grain boundaries between chalcopyrite-tennantite inclusions and the host sphalerite. Interestingly, the inhomogeneous distribution of precious metals and other chalcophile elements is generally concordant with the extent of recrystallization, intragranular porosity as well as various degrees of structural disordering/imperfectness (i.e., bulk defect density) in ZnS domains. Lattice defects and interfaces may play a limited role in promoting the simultaneous introduction of exotic impurities into colloform sphalerite during rapid growth. Even though certain morphological traits and aggregation state at the nanoscale seem to support a biogenic origin of these ZnS particles characterized by admixed polytypic intergrowth structures, the mineralogical and geochemical features of highly-defective sphalerite crystals, in addition to their microscale S-isotope signatures with relatively high δ34S values, exhibit signs of abiologically-mediated, rapid precipitation caused by extensive mixing and cooling at Edmond. The physicochemical conditions and seafloor disequilibrium processes indicated by ZnS formation mechanism might facilitate the incorporation and enrichment of Ag or other trace elements in hydrothermal sphalerite.

Bulk and interface recombination in planar lead halide perovskite solar cells: A Drift-Diffusion study

A theoretical approach based on Drift-Diffusion equations is presented to study planar mixed lead halide perovskite solar cells. Updated physical parameters such as permittivity, mobility, effective density of states and doping density is employed in simulations. Current-voltage curve data for two experimental sample is imported and through fitting with the model, density of bulk and interface defects is calculated. We obtain the bulk defect density around 1016cm−3 and surface recombination velocities in the range of 10cm/s. These values which are in good agreement with experimental measurements and considerably deviated from previous theoretical studies, verify the model and adopted constants. Shockley-Queisser limit is also presented as the ideal device and the effect of bulk and interface defects are presented as loss factors that cause departure from this limit. Our simulations conclude that the overall efficiency of perovskite solar cells is mainly governed by the open-circuit voltage and also identify the interface defects as the major loss factor in these devices.

Controlling the c-Si/a-Si:H interface in silicon heterojunction solar cells fabricated by HWCVD

This paper deals with the engineering of the hetero-interface between intrinsic amorphous silicon (i-a-Si:H) layer and the n-type crystalline silicon (c-Si) wafer during the fabrication of the Silicon Heterojunction (SHJ) solar cell by the Hot Wire Chemical Vapor Deposition technique. It is known that this interface and the associated surface passivation of the c-Si is key to obtaining high efficiency heterojunction solar cells. The monitoring of this interface was carried out using high-resolution transmission electron microscopy (HRTEM). The HRTEM data of the c-Si/a-Si:H interface reveals a drastic dependence on the filament temperature (Tf) used during the deposition of the i-a-Si:H layer. Detailed analysis of the solar cell characteristics indicates that the cells where one has an abrupt crystalline/amorphous interface shows higher conversion efficiency compared to those where we have a rough and a defective interface or where there are indications of local epitaxy in the a-Si:H layer. The second parameter which was engineered is the bulk defect density of the intrinsic a-Si:H layer. Though the thickness of i-a-Si:H layer in case of SHJ solar cells is only around 5nm and serves the purpose of passivating the dangling bonds on the c-Si wafer, the bulk defect density of this layer cannot be ignored. We have achieved a-Si:H films with acceptable bulk defect density without dilution of the silane gas with hydrogen. The bulk defect density of the i-a-Si:H layer has been determined by the constant photocurrent method (CPM) and is correlated to the performance of SHJ solar cells. A direct consequence of these control parameters was observed in the improvement of the external quantum efficiency near 600nm wavelength region.

Defect-dependent stability of highly propylene-selective zeolitic-imidazolate framework ZIF-8 membranes

Membranes of ZIF-8, a prototypical zeolitic-imidazolate framework (ZIF) with a sodalite topology, have shown excellent propylene/propane separation performances based on molecular sieving mechanism. Although the long-term stability of ZIF-8 membranes is of critical importance for their practical applications, there are only a few studies reported on the subject. Here, we report the long-term binary propylene/propane performances of ZIF-8 membranes prepared by two distinctive synthesis methods. A series of characterizations was employed to explain how different synthetic protocols led to the formation of ZIF-8 membranes with different bulk defect densities and surface defects, thereby affecting the long-term membrane stability. Finally, a post-synthetic ligand treatment is proposed as an effective means to mitigate the defects of ZIF-8 membranes, resulting in improved long-term separation performances.

Compositional effects in Ag2ZnSnSe4 thin films and photovoltaic devices

Ag2ZnSnSe4 (AZTSe) is a relatively new n-type photovoltaic (PV) absorber material which has recently demonstrated a conversion efficiency of ∼5% in a Schottky device architecture. To date, little is known about how the influence of composition on AZTSe material properties and the resulting PV performance. In this study, the Ag/Sn ratio is shown to be critical in the controlling grain growth, non-radiative recombination, and the bulk defect structure of the absorber. Insufficient Ag (relative to Zn and Sn) results in small grains, low photoluminescence intensities, and band gap narrowing, possibly due to an increase in the bulk defect density. Additionally, etching the AZTSe films in KCN prior to junction formation is found to be important for achieving reproducible efficiencies. Surface analysis using Auger Nanoprobe Microscopy analysis reveals that a KCN etch can selectively remove potentially harmful Ag-rich secondary phases, therefore improving the MoO3/AZTSe junction quality. Moreover, grain boundaries in AZTSe are found to be enriched in Sn and O following KCN; the role this oxide plays in surface passivation and junction formation has yet to be determined.