Kesterite Solar Cells Research Articles

Energy Band Alignment and Defect Synergistic Regulation Enable Air-Solution-Processed Kesterite Solar Cells With the Lowest VOC Deficit.

The major challenge in preparing high-performance Cu2ZnSn(S,Se)4 solar cells is the large open circuit voltage deficit (VOC-def). A new strategy utilizing the synergistic substitution of Ag and In dual cations has been proposed to simultaneously address the problems of undesirable interface band alignment and high-density detrimental bulk defects, obtaining decreased carrier recombination rate and increased minority carrier lifetime. The shorter In-S/Se bonds move the CBM higher by generating stronger repulsive force than the Sn-S/Se bonds, thus adjusting the interface band alignment. Ag substitution can effectively suppress Cu─Zn disorder, while Ag, In dual substitution can further passivate Sn-related defects and solve the issue of low carrier concentration in Ag single-substituted samples. Besides, the superior carrier property of In-Se materials significantly enhanced the device carrier lifetime and minority carrier diffusion length. The state-of-the-art air-solution-processed CZTSSe device without any addition treatment with 14.33% efficiency and 580mV VOC is obtained, possessing the lowest VOC-def value currently available in the CZTSSe field (VOC/VOC SQ = 64.7%). This work emphasizes the synergistic modulation of band alignment, defect level, grain growth, and carrier transportation by dual cation substitution, which paves a convenient and effective way to realize high-performance solar cells and photovoltaic devices.

Mitigating Band Tailing in Kesterite Solar Absorbers: Ab Initio Quantum Dynamics.

Open-circuit voltage deficits are limiting factors in kesterite solar cells. Addressing this issue by suppressing band tailing and nonradiative charge recombination is essential for enhancing the performance. We employ ab initio nonadiabatic molecular dynamics to elucidate the origin of band tailing and charge losses and propose a mitigation strategy. The simulations show that Cu-Zn disorder, associated with antisite defect clusters [CuZn+ZnCu], is a significant source of band tailing in kesterites, as evidenced by the much larger Urbach energy in disordered than ordered kesterites. Cu-Zn disorder gives rise to new sulfur-centered coordination polyhedra, increases structural inhomogeneity, changes electrostatic potential at sulfur centers, and shifts the S(3p) orbital energy. Differences in the S(3p)/Cu(3d) and S(3p)/Sn(5s) hybridization strengths and the S(3p) orbital energy shift reduce the band gap by 0.37 eV. Furthermore, Cu-Zn disorder enhances vibrational motion of sulfur anions and surrounding cations, increasing band gap fluctuations by 15 meV. The stronger electron-phonon interactions reduce charge carrier lifetimes and limit the kesterite solar cell efficiency. Partial substitution of Zn with Cd facilitates structural ordering and significantly suppresses band tailing, particularly in disordered systems. The improvement can be attributed to the larger atomic radius and mass of Cd, which weakens bonding around the anion, suppresses S-related vibrations within the covalent tetrahedra, and reduces nonadiabatic coupling, thereby increasing charge carrier lifetimes. The reported results establish the key influence of cation disorder on band tailing and reduced charge carrier lifetimes in kesterites and highlight cation disorder engineering as a strategy to achieve high-efficiency kesterite solar cells.

Over 10% Efficiency Pure Sulfide Kesterite Solar Cells on Transparent Electrode with Cd-Ag Co-Alloying.

The environmentally friendly elements composed of high bandgap pure sulfide Cu2ZnSnS4 (CZTS) semiconductor has broad prospects for building integrated photovoltaic, double-sided, and semi-transparent solar cells when fabricated on transparent substrates. The key issues limiting the performance of CZTS solar cells are poor absorber quality and unfavorable band energy alignment causing serious charge carrier recombination. Here, thefabrication of CZTS solar cells are reported on fluorine-doped tin oxide (FTO) substrates from dimethyl sulfoxide solution and the effects of the Cd and Ag alloying on device performance. Characterizations show that Cd alloying greatly decreases defect concentration and converts Cliff-type band alignment to favorable Spike-type, leading to greatly improved current density. Further, Ag alloying eliminates near-horizontal grain boundaries and passivates defects in both bulk and heterojunction interface, resulting in a champion device with a power conversion efficiency of 10.3%, the highest efficiency pure sulfide CZTS solar cell on FTO substrate. The results demonstrate the great application potential of pure sulfide kesterite solar cells.

Reversing band bending at grain boundaries enables high-efficiency Cu2ZnSn(S,Se)4 solar cells

Kesterite solar cells show great potential for sustainable photovoltaic technology, attributed to their excellent semiconductor properties and earth abundant composition. However, undesirable band bending at the grain boundaries (GBs) in Cu2ZnSn(S,Se)4 (CZTSSe) films induces serious carrier recombination because of inhomogeneous distribution of S and Se in the grain interiors (GIs) and at GBs, which results in large open-circuit voltage deficit and overall poor performance of CZTSSe solar cells. Here, a robust hydrothermal sulfurization design has successfully inverted the band bending at the GBs, with advanced cathodoluminescence measurement confirming the transition of carrier collection pathways from the GBs to the GIs, thereby achieving efficient carrier collection within the GIs. Simultaneously, this design has effectively passivated the non-radiative recombination in the GIs, smoothing the way for carrier collection. Ultimately, a 13.7 % efficiency CZTSSe solar cell with 44 % improvement is realized by this process. This study discloses that reversing the band bending at GBs is practical to tailor the carrier collection, and thus pave the pathway for high-efficient photoelectronic devices.

Enhanced Design of Kesterite Solar Cells through High-Throughput Screening and Machine Learning Approaches.

Kesterite Cu2ZnSnS4 (CZTS) is regarded as one of the most promising materials for thin-film solar cells due to its high light absorption capability, composition of earth-abundant and nontoxic elements, and ease of low-cost mass production. Although the certified power conversion efficiency (PCE) of kesterite solar cells has exceeded 14%, this efficiency remains significantly below the Shockley-Queisser limit. In this study, we generated a Perdew-Burke-Ernzerhof (PBE) band gap data set encompassing 263 64-atom species for high-throughput screening by substituting elements at different sites in A2BCX4 quaternary kesterite materials. Additionally, we utilized a symbolic regression method based on genetic programming to explore the functional relationship among the oxidation state, ionic radius, and electronegativity of kesterites with PBE band gaps. Simultaneously, we employed decision tree models (XGBoost, LightGBM, CatBoost, and random forest) and convolutional neural network (CNN) models (CustomCNN, VGG16, DenseNet121, Xception, and EfficientNetV2B0) to predict band gaps, achieving a coefficient of determination (R2) of up to 0.93. Furthermore, we selected 54 kesterite materials with PBE band gaps ranging from 0.4 to 1.5 eV for detailed electronic structure calculations with Heyd-Scuseria-Ernzerhof (HSE06) functional and investigated the effects of B-site atomic substitutions on the performance of solar cell materials. Compared to Ag2CaSnSe4, Ag2SrSnSe4 exhibits fewer deep defects and richer shallow defects, which contribute to an increased carrier concentration and reduced charge and energy losses, making it a superior candidate for solar cell applications.

Interface-Centric Strategies in Kesterite Solar Cells: Addressing Challenges, solutions, and Future Directions for Efficient Solar-Harvesting Technologies.

As reserves of non-renewable energy sources decline, the search for sustainable alternatives becomes increasingly critical. Next-generation energy materials play a key role in this quest by enabling the manipulation of properties for effective energy solutions and understanding interfaces to enhance energy yield. Studying these interfaces is essential for managing charge transport in optoelectronic devices, yet it presents significant challenges. This review emphasizes the critical role of interfaces in kesterite solar cells (KSCs), focusing on interfacial architecture, carrier losses, and non-radiative recombination. This review highlights the importance of addressing interface issues and utilizing advanced characterization tools to reveal interface properties. Current interface problems are addressed, recent advancements in interface engineering are summarized, and perspectives on future challenges and prospects are offered. The goal is to illuminate the nature of interfaces and tackle interface losses, which are crucial for improving device design and performance. Despite their pivotal role in device operation, comprehensive reviews on interfaces are lacking, underscoring the relevance of the work for researchers in material interfaces and device engineering. It is hoped that this article will spark interest and inspire further research into interface studies and the mitigation of interface losses.

8.36% Efficient CZTS Solar Cells on Transparent Electrode via Solution Processing

High‐bandgap Cu2ZnSnS4 (CZTS) thin film solar cells on transparent electrodes show favorable characteristics for new photovoltaic application scenarios including building‐integrated photovoltaics, vehicle‐integrated photovoltaics, and top cell for tandem structure. However, the efficiency of pure sulfide kesterite CZTS thin film solar cells on transparent substrates lags behind that on traditional Mo substrates. Herein, fabrication of high‐quality CZTS absorber films and efficient solar cells on fluorine‐doped tin oxide substrates from dimethyl sulfoxide solution is reported. The formation of harmful secondary phases in CZTS film is suppressed by simply adjusting the chemical stoichiometry in the precursor solution, leading to the development of 5.88% CZTS solar cells. Sodium (Na) doping further promotes grain growth and suppresses secondary phase, contributing to the reduced interface recombination and improved device performance. A champion device with an efficiency of 8.36% has been achieved with 1% Na doping, underscoring the significance of the solution process in achieving highly efficient kesterite solar cells on transparent electrodes.

In Situ Vanadium Modification Induced a Back Interfacial Field Passivation Effect toward Efficient Kesterite Solar Cells beyond 11% Efficiency.

Realization of a high-quality back electrode interface (BEI) with suppressed recombination is crucial for Cu2ZnSn(S,Se)4 (CZTSSe) solar cells. To achieve this goal, the construction of a traditional chemical passivation effect has been widely adopted and investigated. However, there is currently a lack of reports concerning the construction of a field passivation effect (FPE) for the BEI. Herein, considering the characteristic of the negligible difference in ionic radius between Mo (0.65 Å) and V (0.64 Å) as well as the presence of one less valence electron compared to Mo, vanadium (V) was employed and in situ incorporated into the MoSe2 interfacial layer during the deposition of the Mo:V electrode and selenization process. This allowed for the establishment of a desirable in situ VI-FPE interface with p-MoSe2:V/p-CZTSSe at the BEI. The p-type characteristic in MoSe2:V is attributed to the presence of the VMo acceptor; notably, the Fermi energy level of MoSe2:V has shifted downward by 0.62 eV compared to MoSe2, thereby facilitating the formation of an optimized band alignment between MoSe2:V and the absorber. Consequently, the photovoltaic parameters of the cell-FPE have experienced a significant increase due to the enhanced carrier transportation efficiency compared to cell-ref, resulting in a remarkable improvement in efficiency from 8.28 to 11.11%.

Suppressing harmful defects to enhance the performance of kesterite solar cells via extra Mg-doping

Extra-cations doping is known to be an effective approach to control the generation of harmful defects and band-tail states in Cu2ZnSn(S, Se)4 (CZTSSe) solar cells. Here, Mg is used as the extra doped element candidate, the impact of its doping concentration on the composition, structure, morphology, electrical properties, and efficiency of CZTSSe devices is systematically investigated, and its optimal doping concentration is 2 %, which can improve the efficiency of devices from 7.08 % to 9.0 %. The remarkably improved efficiency of the extra Mg-incorporated devices can be explained by the better crystalline quality and fewer deep defects. This work can provide a new approach to boost the performance of kesterite solar cells.

Critical review on the controllable growth and post-annealing on the heterojunction of the kesterite solar cells

Abstract Kesterite-structured solar cells have drawn significant attention due to their low-cost and environmental friendly composition. Recently, a remarkable certified power conversion efficiency (PCE) of 14.9% has been achieved, indicating a broader prospect for kesterite solar cells. However, this PCE is still far below the theoretical efficiency and the PCE of predecessor Cu(In,Ga)Se2 solar cells, which have been commercialized successfully. The relatively low device efficiency primarily originates from the unfavourable bulk and heterojunction of kesterite solar cell. Therefore, the achievement of high PCE in kesterite solar cells heavily relies on high-quality absorber layers and appropriate heterojunction contact. In this review, we first summarize the recent studies on the controllable growth of kesterite thin film. Based on different fabrication methods, various endeavors in revealing the reaction mechanism and manipulating the growth pathway of kesterite thin films have been introduced. Subsequently, studies related to the optimization of heterojunction by post-annealing process are also summarized. This simple and convenient approach can effectively enhance the heterojunction contact and promote the carrier transportation. Finally, this article discusses the future development strategy and perspectives towards achieving enhanced PCE in kesterite thin film solar cells

Introducing Bi2S3 Interlayer to Synergistically Modify Mo Back Contact and Regulate Bulk Defects in Kesterite Solar Cells.

A suitable interlayer between the Mo back electrode and kesterite absorber layer has been proven to have a positive effect on limiting the bulk defects of the absorber by the constitute diffusion. Here, a thin Bi2S3 layer is used as the back-interface intermediate layer for the first time, this innovative approach allows for simultaneous modification of the back contact and reduction of bulk defects, resulting in improving the power conversion efficiency of the kesterite device from 9.66% to 11.8%. The evaporated Bi2O3 thin films turn into the Bi2S3 interlayers after sintering the Cu2ZnSnS4 precursor thin films. The Bi2S3 interlayer can inhibit the decomposition reaction of back contact and suppress the formation of the secondary phases. It can also optimize the Fermi level offset and promote the separation of the photoinduced carriers, resulting from its characteristic of high work function. Besides, a small part of the Bi element can diffuse into Cu2ZnSn(S, Se)4 film and induce the crystal growth and restrain Zn-related defects, which is attributed to forming the low melting-point liquid BiSex phase during the high-temperature selenization process. The conclusions highlight the bifunction of the thin Bi2S3 intermediate layer, which can provide a new approach to improve the photoelectric conversion efficiency of kesterite solar cells.

Viable Strategy for Suppressing Antisite Defects and Band Tailing States in Solution-Processed Kesterite Solar Cells via IIIA Incorporation: Case of Aluminum

Viable Strategy for Suppressing Antisite Defects and Band Tailing States in Solution-Processed Kesterite Solar Cells via IIIA Incorporation: Case of Aluminum

Interfacial Passivation of Kesterite Solar Cells for Enhanced Carrier Lifetime: Ab Initio Nonadiabatic Molecular Dynamics Study

AbstractNonradiative recombination at the front contact interface of kesterite solar cells hinders the extraction of photo‐generated carriers, significantly restricting the efficiency enhancement. However, identifying the recombination centers and proposing effective passivation strategies remain open questions. First‐principles calculations combining with nonadiabatic molecular dynamics (NAMD) simulations unveil that the interfacial translational symmetry breaking in elemental valence states leads to a detrimental donor‐like Cu2ZnSnS4/CdS interface with deep states originating from the interfacial Sn‐5s orbital, which serve as significant nonradiative recombination centers. Here, two mechanisms are proposed for eliminating the deep interface states: 1) directly replacing Sn‐5s with higher outer orbital levels by substituting group IIIA elements (In and Ga) for the interfacial Sn atom; 2) introducing an extra defect‐level coupling with Sn‐5s by substituting group VA elements (N, P, and As) for the S atoms bonded with the interfacial Sn atom. The representative InSn and PS acceptor defects, which are energetically favorable at the detrimental donor‐like interface, effectively passivate the deep interface states, markedly improving the carrier lifetimes by weakening nonadiabatic coupling between the band edge and the interfacial states. This study reveals the origin of the interfacial nonradiative recombination of kesterite solar cells and offers insights into interfacial passivation in semiconductor devices.

Effects of Al2O3 Rear Interface Passivation on the Performance of Bifacial Kesterite‐Based Solar Cells with Fluorine‐Doped Tin Dioxide Back Contact

Herein, ultrathin Al2O3 is investigated as a rear interface passivation layer for kesterite solar cells with F:SnO2 (FTO) back contact for potential performance improvement. On the passivation layer, a thin Mo layer is deposited to improve the FTO's ohmicity. Further, NaF is evaporated on the copper zinc tin sulfide (CZTS) precursors to create openings at the passivation layer and achieve Na‐induced benefits in the absorber. The CZTS absorbers deposited directly on the Al2O3‐coated FTO peel off, while those with Mo interlayer do not. For pure sulfide kesterite devices, the Al2O3 layer reduces the short‐circuit current density (JSC), resulting in poor device efficiency. On the other hand, significantly higher JSC is realized for mixed sulfide and selenide kesterite devices with Al2O3 passivation layer, with the current density–voltage curve suggesting a reduced barrier height at the rear interface. As a result, the efficiency is improved from 1.5% for devices without Al2O3 to 4.6% for those with Al2O3. Likewise, improved external quantum efficiency response is observed in the devices with passivation layer for backside and frontside illumination. Therefore, contribution of Al2O3 passivation layer to the performance of kesterite‐based solar cells is evident from the results of this study.

Kesterite Films Processed with Organic Solvents: Unveiling the Impact of Carbon‐Rich Fine‐Grain‐Layer Formation on Solar‐Cell Performance

Solution‐processed kesterite (copper zinc tin sulfide [CZTS]) solar cells attract significant attention owing to their low cost, ease of large‐scale production, and earth‐abundant elemental composition, which make these devices promising to fulfill the ever‐increasing demand of the photovoltaic (PV) industry. Compared to the performances of expensive vacuum‐based techniques, colloidal nanocrystal kesterite solar cells garner substantial interest due to their economical and rapid processing. Led by the hot‐injection method, organic solvent‐based techniques are widely adopted to realize CZTS nanocrystal inks. With organic solvents, ligand‐stabilized nanoparticles are formed leading to dispersive and homogenous kesterite inks. However, the presence of carbon‐rich ligands around the nanocrystal surface often leads to the formation of a fine‐grain layer that is rich in carbon content. The organic ligands decompose into amorphous carbon residues during a high‐temperature annealing process and hinder the grain growth process. The carbon‐rich fine‐grain (CRFG) layer generally poses a negative influence on the PV performance of the kesterite solar cell; however, few reports maintain their disposition about CRFG as innocuous. In this review study, a detailed discussion on CRFG is presented, aiming to understand the insights about its formation and impact on the device's performance.

Li‐Doping and Ag‐Alloying Interplay Shows the Pathway for Kesterite Solar Cells with Efficiency Over 14%

Li‐Doping and Ag‐Alloying Interplay Shows the Pathway for Kesterite Solar Cells with Efficiency Over 14%

Multinary alloying for facilitated cation exchange and suppressed defect formation in kesterite solar cells with above 14% certified efficiency

Multinary alloying for facilitated cation exchange and suppressed defect formation in kesterite solar cells with above 14% certified efficiency

Pd(II)/Pd(IV) redox shuttle to suppress vacancy defects at grain boundaries for efficient kesterite solar cells

Charge loss at grain boundaries of kesterite Cu2ZnSn(S, Se)4 polycrystalline absorbers is an important cause limiting the performance of this emerging thin-film solar cell. Herein, we report a Pd element assisted reaction strategy to suppress atomic vacancy defects in GB regions. The Pd, on one hand in the form of PdSex compounds, can heterogeneously cover the GBs of the absorber film, suppressing Sn and Se volatilization loss and the formation of their vacancy defects (i.e. VSn and VSe), and on the other hand, in the form of Pd(II)/Pd(IV) redox shuttle, can assist the capture and exchange of Se atoms, thus contributing to eliminating the already-existing VSe defects within GBs. These collective effects have effectively reduced charge recombination loss and enhanced p-type characteristics of the kesterite absorber. As a result, high-performance kesterite solar cells with a total-area efficiency of 14.5% (certified at 14.3%) have been achieved.

Performance optimization of earth abundant CZTS Kesterite solar cell with efficient interface engineering and back surface field

Performance optimization of earth abundant CZTS Kesterite solar cell with efficient interface engineering and back surface field

Segmented Control of Selenization Environment for High-Quality Cu2ZnSn(S,Se)4 Films Toward Efficient Kesterite Solar Cells.

High-crystalline-quality absorbers with fewer defects are crucial for further improvement of open-circuit voltage (VOC) and efficiency of Cu2ZnSn(S,Se)4 (CZTSSe) solar cells. However, the preparation of high-quality CZTSSe absorbers remains challenging due to the uncontrollability of the selenization reaction and the complexity of the required selenization environment for film growth. Herein, a novel segmented control strategy for the selenization environment, specifically targeting the evaporation area of Se, to regulate the selenization reactions and improve the absorber quality is proposed. The large evaporation area of Se in the initial stage of the selenization provides a great evaporation and diffusion flux for Se, which facilitates rapid phase transition reactions and enables the attainment of a single-layer thin film. The reduced evaporation area of Se in the later stage creates a soft-selenization environment for grain growth, effectively suppressing the loss of Sn and promoting element homogenization. Consequently, the mitigation of Sn-related deep-level defects on the surface and in the bulk induced by element imbalance is simultaneously achieved. This leads to a significant improvement in nonradiative recombination suppression and carrier collection enhancement, thereby enhancing the VOC. As a result, the CZTSSe device delivers an impressive efficiency of 13.77% with a low VOC deficit.