Formation of CuInSe2 and CuGaSe2 Thin‐Films Deposited by Three‐Stage Thermal Co‐Evaporation: A Real‐Time X‐Ray Diffraction and Fluorescence Study

Thin film solar cells based on co‐evaporated Cu(In,Ga)Se₂ absorber films present the highest efficiencies among current polycrystalline thin‐film technologies. Thanks to the development of a novel experimental setup for in situ growth studies, it was possible to follow the formation of the crystalline phases during such deposition processes for the first time. This synchrotron‐based energy‐dispersive X‐ray diffraction and fluorescence setup is suited for real‐time studies of thin film vapor deposition processes. Focusing on the growth of CuInSe₂ and CuGaSe₂ fabricated by three‐stage processing, we find that the phase transitions in the Cu‐In‐Se system follow the reported pseudo‐binary In₂Se₃‐Cu₂Se phase diagram. This requires a transformation of the Se sublattice during the incorporation of Cu‐Se into the In₂Se₃ precursor film from the first process stage. In the Cu‐Ga‐Se system, besides an increase in the lattice spacings, we observe no transformation of the Se sublattice. Furthermore, the structural defects of the Ga‐Se precursor film are preserved until the CuGaSe₂ stoichiometry is reached. By means of model calculations of the fluorescence signals, we confirm in both systems the segregation of Cu₂Se at the surface near a concentration of 25 at.% Cu shortly after the recrystallization of the films. The modeling also reveals that Cu₂Se penetrates into the CuInSe₂ film, whereas it remains at the surface of the CuGaSe₂ film.     

Efficient and Stable TiO2:Pt–Cu(In,Ga)Se2 Composite Photoelectrodes for Visible Light Driven Hydrogen Evolution

Novel thin film composite photocathodes based on device‐grade Cu(In,Ga)Se₂ chalcopyrite thin film absorbers and transparent conductive oxide Pt‐implemented TiO₂ layers on top are presented for an efficient and stable solar‐driven hydrogen evolution. Thin films of phase‐pure anatase TiO₂ are implemented with varying Pt‐concentrations in order to optimize simultaneously i) conductivity of the films, ii) electrocatalytic activity, and iii) light‐guidance toward the chalcopyrite. Thereby, high incident‐photon‐to‐current‐efficiencies of more than 80% can be achieved over the full visible light range. In acidic electrolyte (pH 0.3), the most efficient Pt‐implemented TiO₂–Cu(In,Ga)Se₂ composite electrodes reveal i) photocurrent densities up to 38 mA cm^?2 in the saturation region (?0.4 V RHE, reversible hydrogen electrode), ii) 15 mA cm^?2 at the thermodynamic potential for H₂‐evolution (0 V RHE), and iii) an anodic onset potential shift for the hydrogen evolution (+0.23 V RHE). It is shown that the gradual increase of the Pt‐concentration within the TiO₂ layers passes through an efficiency‐ and stability‐maximum of the device (5 vol% of Pt precursor solution). At this maximum, optimized light‐incoupling into the device‐grade chalcopyrite light‐absorber as well as electron conductance properties within the surface layer are achieved while no degradation are observed over more than 24 h of operation.     

Atomic‐Scale Observation of Oxygen Substitution and Its Correlation with Hole‐Transport Barriers in Cu2ZnSnSe4 Thin‐Film Solar Cells

Kesterite‐type Cu₂ZnSn(S,Se)₄ has been extensively studied over the past several years, with researchers searching for promising candidates for indium‐ and gallium‐free inexpensive absorbers in high‐efficiency thin‐film solar cells. Many notable experimental and theoretical studies have dealt with the effects of intrinsic point defects, Cu/Zn/Sn nonstoichiometry, and cation impurities on cell performance. However, there have been few systematic investigations elucidating the distribution of oxygen at an atomic scale and the correlation between oxygen substitution and charge transport despite unavoidable incorporation of oxygen from the ambient atmosphere during thin‐film fabrication. Using energy‐dispersive X‐ray spectroscopy, scanning transmission electron microscopy, and electron energy‐loss spectroscopy, the presence of nanoscale layers is directly demonstrated in which oxygen is substantially substituted for Se, near grain boundaries in polycrystalline Cu₂ZnSnSe₄ films. Density‐functional theory calculations also show that oxygen substitution remarkably lowers the valence band maximum and subsequently widens the overall bandgap. Consequently, anion modification by oxygen can make a major contribution to the formation of a robust barrier blocking the holes from bulk grains into grain boundaries, thereby efficiently attaining electron?hole separation. The findings provide crucial insights into achieving better energy conversion efficiency in kesterite‐based thin‐film solar cells through optimum control of oxidation during the fabrication process.     

Chalcopyrite Semiconductors for Quantum Well Solar Cells

The possibilities of using highly absorbing chalcopyrite semiconductors of the type Cu(In,Ga)Se₂ in a quantum well solar cell structure are explored. Thin alternating layers of 50 nm CuInSe₂ and CuGaSe₂ were grown epitaxially on a GaAs(100) substrate. The optical properties of a resulting structure of three layers indicate charge carrier confinement in the low band gap CuInSe₂ layer. By compositional analysis interdiffusion of In and Ga at the interfaces was found. The compositional profile was converted into a conduction‐band diagram, for which the quantization of energy levels was numerically confirmed using the effective‐mass approximation. The results provide a promising basis for the future development of chalcopyrite‐type quantum well structures and their application, i.e. in quantum well solar cells.     

Engineering Grain Boundaries in Cu2ZnSnSe4 for Better Cell Performance: A First‐Principle Study

Through first‐principle density functional theory (DFT) calculations, the atomic structure and electronic properties of intrinsic and passivated Σ3 (114) grain boundaries (GBs) in Cu₂ZnSnSe₄ (CZTSe) are studied. Intrinsic GBs in CZTSe create localized deep states within the band gap and thus act as Shockley‐Read‐Hall recombination centers, which are detrimental to cell performance. Defects, such as Zn_Sn (Zn atoms on Sn sites), Na⁺_i (interstitial Na ions), and O_Se (O atoms on Se sites), prefer to segregate into GBs in CZTSe. The segregation of these defects at GBs exhibit two beneficial effects: 1) eliminating the deep gap states via wrong bonds breaking or weakening at GBs, making GBs electrically benign; and 2) creating hole barriers and electron sinkers, promoting effective charge separation at GBs. The results suggest a unique chemical approach for engineering GBs in CZTSe to achieve improved cell performance.     

Defects in Cu(In,Ga)Se2 Chalcopyrite Semiconductors: A Comparative Study of Material Properties,Defect States,and Photovoltaic Performance

Understanding defects in Cu(In,Ga)(Se,S)₂ (CIGS), especially correlating changes in the film formation process with differences in material properties, photovoltaic (PV) device performance, and defect levels extracted from admittance spectroscopy, is a critical but challenging undertaking due to the complex nature of this polycrystalline compound semiconductor. Here we present a systematic comparative study wherein varying defect density levels in CIGS films were intentionally induced by growing CIGS grains using different selenium activity levels. Material characterization results by techniques including X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, secondary ion mass spectrometry, X‐ray photoelectron spectroscopy, and medium energy ion scattering indicate that this process variation, although not significantly affecting CIGS grain structure, crystal orientation, or bulk composition, leads to enhanced formation of a defective chalcopyrite layer with high density of indium or gallium at copper antisite defects ((In, Ga)_Cu) near the CIGS surface, for CIGS films grown with insufficient selenium supply. This defective layer or the film growth conditions associated with it is further linked with observed current‐voltage characteristics, including rollover and crossover behavior, and a defect state at around 110 meV (generally denoted as the N1 defect) commonly observed in admittance spectroscopy. The impact of the (In, Ga)_Cu defects on device PV performance is also established.     

Over 14% Efficiency of Directly Sputtered Cu(In,Ga)Se2 Absorbers without Postselenization by Post‐Treatment of Alkali Metals

Direct sputtering of a single quaternary Cu(In,Ga)Se₂ (CIGS) target without postselenization is a promising approach to fabricating CIGS absorbers. However, the device efficiency of the quaternary‐sputtered CIGS is limited to 10%–11% due to the low and uncontrollable Se supply during the quaternary sputtering process. Here, an enhanced efficiency of 14.1% is reported by directly sputtering from a CIGS target without extra Se supply followed by sequential postdeposition treatments (PDT) of NaF and KF. The effects of different post‐treatments of alkali metals on quaternary‐sputtered CIGS thin films are discussed in detail. A Cu‐depleted surface is not observed in the quaternary‐sputtered CIGS thin films after KF‐PDT, different from the observation in the coevaporated CIGS, in which the Cu‐depleted surface layer induced by KF‐PDT enhances the efficiency. On the other hand, it is found that KF‐PDT reduces Se vacancies more effectively than NaF‐PDT, which could be another electrically benign behavior of KF‐PDT. The effective passivation of Se vacancies after KF‐PDT overcomes the Se‐poor nature of the quaternary sputtering process without postselenization. Therefore, KF‐PDT combined with Na doping, which is known to annihilate In_Cu defects, significantly improves minority carrier lifetime and cell performance.     

Development of MoS2–CNT Composite Thin Film from Layered MoS2 for Lithium Batteries

Layered MoS₂ prepared by liquid‐phase exfoliation has been blended with single‐walled carbon nanotubes (SWNTs) to form novel composite thin films for lithium battery applications. The films were formed by vacuum filtration of blended dispersions onto nitrocellulose membranes. The resulting composite films were transferred onto Cu foil electrodes via a facile filtration/wet transfer technique from nitrocellulose membranes. The morphology of the film was characterised by field emission scanning electron microscopy, which suggests that the MoS₂‐SWNT composite film shows good adherence to the Cu foil substrate. The MoS₂‐SWNT composite thin films show strong electrochemical performance at different charge‐discharge rates. The capacity of a MoS₂‐SWNT composite film with thickness of 1 μm is approximately 992 mAh g^?1 after 100 cycles. The morphology study showed that the MoS₂‐SWNT thin film retains structural integrity after 100 cycles, while the MoS₂ thin film without SWNTs displays significant cracking. In addition, the novel composite thin film preparation and transfer protocols developed in this study could be extended to the preparation of various layered‐material‐based composite films, with the potential for new device designs for energy applications.     

Defect Engineering in Multinary Earth‐Abundant Chalcogenide Photovoltaic Materials

Application of zinc‐blende‐related chalcogenide absorbers such as CdTe and Cu(In,Ga)Se₂ (CIGSe) has enabled remarkable advancement in laboratory‐ and commercial‐scale thin‐film photovoltaic performance; however concerns remain regarding the toxicity (CdTe) and scarcity (CIGSe/CdTe) of the constituent elements. Recently, kesterite‐based Cu₂ZnSn(S,Se)₄ (CZTSSe) materials have emerged as attractive non‐toxic and earth‐abundant absorber candidates. Despite the similarities between CZTSSe and CIGSe/CdTe, the record power conversion efficiency of CZTSSe solar cells (12.6%) remains significantly lower than that of CIGSe (22.6%) and CdTe (22.1%) devices, with the performance gap primarily being attributed to cationic disordering and associated band tailing. To capture the promise of kesterite‐like materials as prospective “drop‐in” earth‐abundant replacements for closely‐related CIGSe, current research has focused on several key directions to control disorder, including: (i) examination of the interaction between processing conditions and atomic site disorder, (ii) isoelectronic cation substitution to introduce ionic size mismatch, and (iii) structural diversification beyond the zinc‐blende‐type coordination environment. In this review, recent efforts targeting accurate identification and engineering of anti‐site disorder in kesterite‐based CZTSSe are considered. Lessons learned from CZTSSe are applied to other complex chalcogenide semiconductors, in an effort to develop promising pathways to avoid anti‐site disordering and associated band tailing in future high‐performance earth‐abundant photovoltaic technologies.     

Solution‐Processed TiO2 Nanoparticles as the Window Layer for CuIn(S,Se)2 Devices

As a wide‐bandgap semiconductor, titanium dioxide (TiO₂) with a porous structure has proven useful in dye‐sensitized solar cells, but its application in low‐cost, high‐efficiency inorganic photovoltaic devices based on materials such as Cu(InGa)Se₂ or Cu₂ZnSnS₄ is limited. Here, a thin film made from solution‐processed TiO₂ nanocrystals is demonstrated as an alternative to intrinsic zinc oxide (i‐ZnO) as the window layer of CuInS_xSe_1?x solar cells. The as‐synthesized, well‐dispersed, 6 nm TiO₂ nanocrystals are assembled into thin films with controllable thicknesses of 40, 80, and 160 nm. The TiO₂ nanocrystal films with thicknesses of 40 and 80 nm exhibit conversion efficiencies (6.2% and 6.33%, respectively) that are comparable to that of a layer of the typical sputtered i‐ZnO (6.42%). The conversion efficiency of the devices with a TiO₂ thickness of 160 nm decreases to 2.2%, owing to the large series resistance. A 9‐hour reaction time leads to aggregated nanoparticles with a much‐lower efficiency (2%) than that of the well‐dispersed TiO₂ nanoparticles prepared using a 15‐hour reaction time. Under optimized conditions, the champion TiO₂ nanocrystal‐film‐based device shows even higher efficiency (9.2%) than a control device employing a typical i‐ZnO film (8.6%).     

Kesterite Thin‐Film Solar Cells: Advances in Materials Modelling of Cu2ZnSnS4

Quaternary semiconducting materials based on the kesterite (A₂BCX₄) mineral structure are the most promising candidates to overtake the current generation of light‐absorbing materials for thin‐film solar cells. Cu₂ZnSnS₄ (CZTS), Cu₂ZnSnSe₄ (CZTSe) and their alloy Cu₂ZnSn(Se,S)₄ consist of abundant, low‐cost and non‐toxic elements, unlike current CdTe and Cu(In,Ga)Se₂ based technologies. Zinc‐blende related structures are formed by quaternary compounds, but the complexity associated with the multi‐component system introduces difficulties in material growth, characterization, and application. First‐principles electronic structure simulations, performed over the past five years, that address the structural, electronic, and defect properties of this family of compounds are reviewed. Initial predictions of the bandgaps and crystal structures have recently been verified experimentally. The calculations highlight the role of atomic disorder on the cation sub‐lattice, as well as phase separation of Cu₂ZnSnS₄ into ZnS and CuSnS₃, on the material performance for light‐to‐electricity conversion in photovoltaic devices. Finally, the current grand challenges for materials modeling of thin‐film solar cells are highlighted.     

Aging Effect of a Cu(In,Ga)(S,Se)2 Absorber on the Photovoltaic Performance of Its Cd‐Free Solar Cell Fabricated by an All‐Dry Process: Its Carrier Recombination Analysis

Cd‐free Cu(In,Ga)(S,Se)₂ (CIGSSe) solar cells are fabricated by an all‐dry process (a Cd‐free and all‐dry process CIGSSe solar cell) with aged CIGSSe thin film absorbers. The aged CIGSSe thin films are kept in a desiccator cabinet under partial pressure of oxygen of ≈200 Pa for aging time up to 10 months. It is reported for the first time that aged CIGSSe thin film with increased aging time results in significant enhancement of photovoltaic performance of Cd‐free and all‐dry process CIGSSe solar cells, regardless of the alkali treatment. Based on carrier recombination analysis, carrier recombination rates at the interface and in the depletion region of the Cd‐free and all‐dry process CIGSSe solar cells are reduced owing to avoidance of sputtering damage on CIGSSe absorber surface, which is consistent with the strong electron beam‐induced current signal near CIGSSe surface after the increased aging time. It is implied that the interface and near‐surface qualities are clearly improved through the increased aging time, which is attributable to the self‐forming of In_x(O,S)_y near CIGSSe surface, which acts as a buffer layer. Ultimately, the 22.0%‐efficient Cd‐free CIGSSe solar cell fabricated by all‐dry process is achieved with the aged Cs‐treated CIGSSe absorber with the aging time of 10 months.     

A Bottom‐Up Approach toward All‐Solution‐Processed High‐Efficiency Cu(In,Ga)S2 Photocathodes for Solar Water Splitting

The development of solution‐processable routes to prepare efficient photoelectrodes for water splitting is highly desirable to reduce manufacturing costs. Recently, sulfide chalcopyrites (Cu(In,Ga)S₂) have attracted attention as photocathodes for hydrogen evolution owing to their outstanding optoelectronic properties and their band gap—wider than their selenide counterparts—which can potentially increase the attainable photovoltage. A straightforward and all‐solution‐processable approach for the fabrication of highly efficient photocathodes based on Cu(In,Ga)S₂ is reported for the first time. It is demonstrated that semiconductor nanocrystals can be successfully employed as building blocks to prepare phase‐pure microcrystalline thin films by incorporating different additives (Sb, Bi, Mg) that promote the coalescence of the nanocrystals during annealing. Importantly, the grain size is directly correlated to improved charge transport for Sb and Bi additives, but it is shown that secondary effects can be detrimental to performance even with large grains (for Mg). For optimized electrodes, the sequential deposition of thin layers of n‐type CdS and TiO₂ by solution‐based methods, and platinum as an electrocatalyst, leads to stable photocurrents saturating at 8.0 mA cm^–2 and onsetting at ≈0.6 V versus RHE under AM 1.5G illumination for CuInS₂ films. Electrodes prepared by our method rival the state‐of‐the‐art performance for these materials.     

Atomic Layer Deposition of Tin Monosulfide Thin Films

Thin film solar cells made from earth‐abundant, non‐toxic materials are needed to replace the current technology that uses Cu(In,Ga)(S,Se)₂ and CdTe, which contain scarce and toxic elements. One promising candidate absorber material is tin monosulfide (SnS). In this report, pure, stoichiometric, single‐phase SnS films were obtained by atomic layer deposition (ALD) using the reaction of bis(N,N′‐diisopropylacetamidinato)tin(II) [Sn(MeC(N‐ⁱPr)₂)₂] and hydrogen sulfide (H₂S) at low temperatures (100 to 200 °C). The direct optical band gap of SnS is around 1.3 eV and strong optical absorption (α > 10⁴ cm^?1) is observed throughout the visible and near‐infrared spectral regions. The films are p‐type semiconductors with carrier concentration on the order of 10¹⁶ cm^?3 and hole mobility 0.82–15.3 cm²V^?1s^?1 in the plane of the films. The electrical properties are anisotropic, with three times higher mobility in the direction through the film, compared to the in‐plane direction.     

Si‐Doped Cu(In,Ga)Se2 Photovoltaic Devices with Energy Conversion Efficiencies Exceeding 16.5% without a Buffer Layer

In this communication, novel and simplified structure Cu(In,Ga)Se₂ (CIGS) solar cells, which nominally consist of only a CIGS photoabsorber layer sandwiched between back and front contact layers but yet demonstrate high photovoltaic efficiencies, are reported. To realize this accomplishment, Si‐doped CIGS films grown by the three‐stage coevaporation method, B‐doped ZnO transparent conductive oxide front contact layers deposited by chemical vapor deposition, and heat–light soaking treatments are used. Si‐doping of CIGS films is found to modify the film surfaces and grain boundary properties and also affect the alkali metal distribution profiles in CIGS films. These effects are expected to contribute to improvements in buffer‐free CIGS device performance. Heat–light soaking treatments, which are occasionally performed to improve conventional buffer‐based CIGS device performance, are found to be also effective in enhancing buffer‐free CIGS photovoltaic efficiencies. This result suggests that the mechanism behind the beneficial effects of heat–light soaking treatments originates from CIGS bulk issues and is independent of the buffer materials. Consequently, over 16.5% efficiencies, including an independently certified value, are demonstrated from completely buffer‐free CIGS photovoltaic devices.     

Dielectric Dispersion in Ga<Subscript>2</Subscript>S<Subscript>3</Subscript> Thin Films

In this work, the structural, compositional, optical, and dielectric properties of Ga₂S₃ thin films are investigated by means of X-ray diffraction, scanning electron microscopy, energy dispersion X-ray analysis, and ultraviolet—visible light spectrophotometry. The Ga₂S₃ thin films which exhibited amorphous nature in its as grown form are observed to be generally composed of 40.7 % Ga and 59.3 % S atomic content. The direct allowed transitions optical energy bandgap is found to be 2.96 eV. On the other hand, the modeling of the dielectric spectra in the frequency range of 270–1,000 THz, using the modified Drude-Lorentz model for electron-plasmon interactions revealed the electrons scattering time as 1.8 (fs), the electron bounded plasma frequency as ~0.76–0.94 (GHz) and the reduced resonant frequency as 2.20–4.60 ×10¹⁵ (Hz) in the range of 270–753 THz. The corresponding drift mobility of electrons to the terahertz oscillating incident electric field is found to be 7.91 (cm ²/Vs). The values are promising as they nominate the Ga₂S₃ thin films as effective candidates in thin-film transistor and gas sensing technologies.     

Direct Imaging of Cl‐ and Cu‐Induced Short‐Circuit Efficiency Changes in CdTe Solar Cells

To achieve high‐efficiency polycrystalline CdTe‐based thin‐film solar cells, the CdTe absorbers must go through a post‐deposition CdCl₂ heat treatment followed by a Cu diffusion step. To better understand the roles of each treatment with regard to improving grains, grain boundaries, and interfaces, CdTe solar cells with and without Cu diffusion and CdCl₂ heat treatments are investigated using cross‐sectional electron beam induced current, electron backscatter diffraction, and scanning transmission electron microscope techniques. The evolution of the cross‐sectional carrier collection profile due to these treatments that cause an increase in short‐circuit current and higher open‐circuit voltage are identified. Additionally, an increased carrier collection in grain boundaries after either/both of these treatments is revealed. The increased current at the grain boundaries is shown to be due to the presence of a space charge region with an intrinsic carrier collection profile width of ≈350 nm. Scanning transmission electron microscope electron‐energy loss spectroscopy shows a decreased Te and increased Cl concentration in grain boundaries after treatment, which causes the inversion. Each treatment improves the overall carrier collection efficiency of the cell separately, and, therefore, the benefits realized by each treatment are shown to be independent of each other.     

Microstructure of Nanoscaled La0.6Sr0.4CoO3‐δ Cathodes for Intermediate‐Temperature Solid Oxide Fuel Cells

Nanocrystalline La_1‐xSr_xCoO_3‐δ (LSC) thin films with a nominal Sr‐content of x = 0.4 were deposited on Ce_0.9Gd_0.1O_1.95 electrolyte substrates using a low temperature sol‐gel process. The structural and chemical properties of the LSC thin films were studied after thermal treatment, which included a calcination step and a variable, extended annealing time at 700 °C or 800 °C. Transmission electron microscopy combined with selected‐area electron diffraction, energy‐dispersive X‐ray spectrometry, and scanning transmission electron microscopy tomography was applied for the investigation of grain size, porosity, microstructure, and analysis of the local chemical composition and element distribution on the nanoscale. The area specific resistance (ASR) values of the thin film LSC cathodes, which include the lowest ASR value reported so far (ASR_chem = 0.023 Ωcm² at 600 °C) can be interpreted on the basis of the structural and chemical characterization.     

Atmospheric‐Pressure Chemical Vapor Deposition of Iron Pyrite Thin Films

Iron pyrite (cubic FeS₂) is a promising candidate absorber material for earth‐abundant thin‐film solar cells. In this report, single‐phase, large‐grain, and uniform polycrystalline pyrite thin films are fabricated on glass and molybdenum‐coated glass substrates by atmospheric‐pressure chemical vapor deposition (AP‐CVD) using the reaction of iron(III) acetylacetonate and tert‐butyl disulfide in argon at 300 °C, followed by sulfur annealing at 500–550 °C to convert marcasite impurities to pyrite. The pyrite‐marcasite phase composition depends strongly on the concentration of sodium in the growth substrate and the sulfur partial pressure during annealing. Phase and elemental composition of the films are characterized by X‐ray diffraction, Raman spectroscopy, Auger electron spectroscopy, secondary ion mass spectrometry, Rutherford backscattering spectrometry, and X‐ray photoelectron spectroscopy. The in‐plane electrical properties are surprisingly insensitive to phase and elemental impurities, with all films showing p‐type, thermally activated transport with a small activation energy (≈30 meV), a room‐ temperature resistivity of ≈1 Ω cm, and low mobility. These ubiquitous electrical properties may result from robust surface effects. These CVD pyrite thin films are well suited to fundamental electrical studies and the fabrication of pyrite photovoltaic device stacks.     

Is the Cu/Zn Disorder the Main Culprit for the Voltage Deficit in Kesterite Solar Cells?

Photovoltaic thin film solar cells based on kesterite Cu₂ZnSn(S_x,Se_1–x)₄ compounds (CZTSSe) have reached >12% sunlight‐to‐electricity conversion efficiency. This is still far from the >20% record devices known in Cu(In_1–y,Ga_y)Se₂ and CdTe parent technologies. A selection of >9% CZTSSe devices reported in the literature is examined to review the progress achieved over the past few years. These devices suffer from a low open‐circuit voltage (V_oc) never better than 60% of the V_{oc max}, which is expected from the Shockley‐Queisser radiative limit (S‐Q limit). The possible role of anionic (S/Se) distribution and of cationic (Cu/Zn) disorder on the V_oc deficit and on the ultimate photovoltaic performance of kesterite devices, are clarified here. While the S/Se anionic distribution is expected to be homogeneous for any ratio x, some grain‐to‐grain and other non‐uniformity over larger area can be found, as quantified on our CZTSSe films. Nevertheless, these anionic distributions can be considered to have a negligible impact on the V_oc deficit. On the Cu/Zn order side, even though significant bandgap changes (>10%) can be observed, a similar conclusion is brought from experimental devices and from calculations, still within the radiative S‐Q limit. The implications and future ways for improvement are discussed.