Enhancement in the Efficiency of Sb2 Se3 Solar Cells by Triple Function of Lithium Hydroxide Modified at the Back Contact Interface

Post-deposition Treatment of Sb2Se3 Enables Defect Passivation and Increased Carrier Transport Dimension for Efficient Solar Cell Application

Post-deposition treatment in thin film preparation can compensate for the inability of directly deposited films by fundamentally altering the chemical, electrical, morphological and defect properties. However, as an emerging photovoltaic material, the synthesis of Sb2Se3 film has so far been unable to effectively adjust the carrier transport and defect properties, thereby hindering performance improvement. In this study, we report that P2O5 can serve as a post-deposition treatment material to modify the chemical and electrical properties of Sb2Se3 thin films. Through experimental analysis, we discover that P atoms from P2O5 can occupy the Se vacancy and convert the deep-level anti-site defect (SbSe) to a shallower defect (PSe), rendering efficient defect passivation. Simultaneously, P-doping induced lattice distortion closes the ribbon spacing of (Sb4Se6)n, promoting efficient carrier transport from one dimension to three dimensions. This structure reduces the restriction of carrier transport in low-dimensional materials, which suppresses the carrier non-radiative recombination and improves the carrier transport efficiency. As a result, we achieved a champion power conversion efficiency of 9.50 % in thermal evaporation derived Sb2Se3 superstrate solar cells. This study provides a novel strategy and guidance for passivating deep-level defects and modifying the crystal structure of low-dimensional solar cell materials.

Wide Bandgap Tellurium Oxide Semiconductor as A Back Contact Modifier for Efficient n-i-p Sb2Se3 Solar Cells

The wide-bandgap and p-type semiconductor layer plays a crucial role in the antimony selenide (Sb2Se3) solar cells, as it can provide carrier confinement and inhibit interface recombination. In this work, the tellurium (Te) thin layer is innovatively applied in superstrate Sb2Se3 solar cells, which is further in situ oxidized to wide-bandgap (3.67 eV) tellurium oxide (TeOx). Experimental results indicate that both Te and TeOx layers can enhance the built-in potential and depletion width of devices and reduce nonradiative recombination at back interfaces. Furthermore, the TeOx layer enables better hole transportation due to the favorable band alignment at Sb2Se3/TeOx interfaces. As a congener of Selenium (Se), the Te component of TeOx is found to effectively passivate the selenium vacancy (VSe) defects at the surface of Sb2Se3 absorbers. Consequently, the all-inorganic devices with TeOx show a high voltage of 0.463 V and a champion power conversion efficiency of 9.67%, which is one of the highest efficiencies for the Sb2Se3 solar cells based on vacuum coating technology. This study provides a unique and useful back contact modification strategy for high-performance Sb2Se3 solar cells.

PO4 3- Tetrahedron Assisted Chelate Engineering for 10.67%-Efficient Antimony Selenosulfide Solar Cells

Anisotropic carrier transport and deep-level defect of antimony selenosulfide (Sb2(S,Se)3) absorber are two vital auses restraining the photovoltaic performance of this emerging thin-film solar cell. Herein, chelate engineering is proposed to prepare high-quality Sb2(S,Se)3 film based on hydrothermal deposition approach, which realizes desirable carrier transport and passivated defects by using tetrahedral PO4 3- ion in dibasic sodium phosphate (Na2HPO4, DSP). The PO4 3- Lewis structure, on one hand in the form of [(SbO)3(PO4)] chelate, can adsorb on the polar planes of cadmium sulfide (CdS) layer, promoting the heterogeneous nucleation, and on the other hand, the tetrahedral PO4 3- inhibits horizontal growth of (Sb4S(e)6)n ribbons due to size effects, thus achieving desirable [hk1] orientation. Moreover, the introduction PO4 3- effectively passivates the antisite defect SbS1. These synergistic effects have effectively improved carrier transport and reduced non-radiative recombination of the Sb2(S,Se)3 absorber. Consequently, the DSP-modified Sb2(S,Se)3 device efficiency increases from 8.59% to 10.67%.

Boron Trioxide-Assisted Post-Annealing Enables Vertical Oriented Recrystallization of Sb2Se3 Thin Film for High-Efficiency Solar Cells

Crystallization process is critical for enhancing the crystallinity, regulating the crystal orientation of polycrystalline thin films, as well as repairing defects within the films. For quasi-1D Sb2Se3 photovoltaic materials, the preparation of Sb2Se3 thin films still faces great challenges in adjusting orientation and defect properties, which limits the device performance. In this study, a novel post-treatment strategy is developed that uses a low melting point B2O3 coating layer as a flux to drive the recrystallization of Sb2Se3, thereby regulating the micro-orientation of thermal evaporation-derived Sb2Se3 films and optimizing their electrical properties. Mechanistic investigations show that B2O3 exhibits stronger adsorption with (hk1) planes of Sb2Se3 to induce a vertical orientation growth of the film, while blocking the volatilization channels of Se and inhibiting Se vacancy defects by interacting with Sb2Se3. The Sb2Se3 film with [hk1] preferential orientation and suppressed deep-level defects promotes the effective transport of charge carriers in solar cells. As a result, the B2O3-treated device delivers a champion efficiency of 9.37% without MgF2 anti-reflection coating, which is currently the highest efficiency in Sb2Se3 solar cells achieved by thermal evaporation method. This study provides a new method and mechanism for regulating optical and electrical properties of low-dimensional inorganic thin films.

Heterogeneous Nucleation Regulation Amends Unfavorable Crystallization Orientation and Defect Features of Antimony Selenosulfide Film for High-Efficient Planar Solar Cells

Antimony selenosulfide (Sb2(S,Se)3) has obtained widespread concern for photovoltaic applications as a light absorber due to superior photoelectric features. Accordingly, various deposition technologies have been developed in recent years, especially hydrothermal deposition method, which has achieved a great success. However, device performances are limited with severe carrier recombination, relating to the quality of absorber and interfaces. Herein, bulk and interface defects are simultaneously suppressed by regulating heterogeneous nucleation kinetics with barium dibromide (BaBr2) introduction. In details, the Br adsorbs and dopes on the polar planes of cadmium sulfide (CdS) buffer layer, promoting the exposure of nonpolar planes of CdS, which facilitates the favorable growth of [hk1]-Sb2(S,Se)3 films possessing superior crystallinity and small interface defects. Additionally, the Se/S ratio is increased due to the replacement of Se by Br, causing a downshift of the Fermi levels with a benign band alignment and a shallow-level defect. Moreover, Ba2+ is located at grain boundaries by coordination with S and Se ions, passivating grain boundary defects. Consequently, the efficiency is increased from 7.70 % to 10.12 %. This work opens an avenue towards regulating the heterogeneous nucleation kinetics of Sb2(S,Se)3 film deposited via hydrothermal deposition approach to optimize its crystalline orientation and defect features.

Rapid Thermal-Driven Crystal Growth and Defect Suppression in Antimony Selenide Thin Film for Efficient Solar Cells

Antimony selenide (Sb2Se3) has demonstrated considerable potential and advancement as a light-absorbing material for thin-film solar cells owing to its exceptional optoelectronic characteristics. However, challenges persist in the crystal growth, particularly regarding the nucleation mechanism during pre-selenization process for Sb2Se3. The defects originating from this process significantly impact the quality of the absorber layer, leading to the degradation in the power conversion efficiency (PCE) of the device. Herein, the evolution of pre-selenization using rapid thermal processing (RTP) on the crystallization quality of Sb2Se3 film is systematically investigated. By optimizing the initial nucleation process during pre-selenization, resulting in a reduction of grain boundaries and nucleation centers, the Sb2Se3 thin films demonstrate enhanced crystallinity and pinholes-free morphology. It is found that the improved quality of the grain interior and interfaces of the Sb2Se3 absorber can mitigate intrinsic defects within the bulk layer, and passivate interfacial defect recombination. As a result, the short circuit current density (JSC) is elevated to 28.97 mA cm-2, and a competitive efficiency of 9.03% is achieved in Sb2Se3 device. This study provides comprehensive insight into the process of crystal growth and the mechanism for defect suppression, which holds guiding significance for advancing photovoltaic performance.

Optimizing Crystal Orientation and Defect Mitigation in Antimony Selenide Thin-Film Solar Cells through Buffer Layer Energy Band Adjustment

Antimony selenide (Sb2Se3) has sparked significant interest in high-efficiency photovoltaic applications due to its advantageous material and optoelectronic properties. In recent years, there has been considerable development in this area. Nonetheless, defects and suboptimal [hk0] crystal orientation expressively limit further device efficiency enhancement. This study used Zinc (Zn) to adjust the interfacial energy band and strengthen carrier transport. For the first time, it is discovered that the diffusion of Zn in the cadmium sulfide (CdS) buffer layer can affect the crystalline orientation of the Sb2Se3 thin films in the superstrate structure. The effect of Zn diffusion on the morphology of Sb2Se3 thin films with CdxZn1-xS buffer layer has been investigated in detail. Additionally, Zn doping promotes forming Sb2Se3 thin films with the desired [hk1] orientation, resulting in denser and larger grain sizes which will eventually regulate the defect density. Finally, based on the energy band structure and high-quality Sb2Se3 thin films, this study achieves a champion power conversion efficiency (PCE) of 8.76%, with a VOC of 458 mV, a JSC of 28.13 mA cm-2, and an FF of 67.85%. Overall, this study explores the growth mechanism of Sb2Se3 thin films, which can lead to further improvements in the efficiency of Sb2Se3 solar cells.

Unveiling Local Current Behavior and Manipulating Grain Homogenization of Perovskite Films for Efficient Solar Cells

Achieving high power conversion efficiency in perovskite solar cells (PSCs) heavily relies on fabricating homogeneous perovskite films. However, understanding microscopic-scale properties such as current generation and open-circuit voltage within perovskite crystals has been challenging due to difficulties in quantifying intragrain behavior. In this study, the local current intensity within state-of-the-art perovskite films mapped by conductive atomic force microscopy reveals a distinct heterogeneity, which exhibits a strong anticorrelation to the external biases. Particularly under different external bias polarities, specific regions in the current mapping show contrasting conductivity. Moreover, grains oriented differently exhibit varied surface potentials and currents, leading us to associate this local current heterogeneity with the grain orientation. It was found that the films treated with isopropanol exhibit ordered grain orientation, demonstrating minimized lattice heterogeneity, fewer microstructure defects, and reduced electronic disorder. Importantly, devices exhibiting an ordered orientation showcase elevated macroscopic optoelectronic properties and boosted device performance. These observations underscore the critical importance of fine-tuning the grain homogenization of perovskite films, offering a promising avenue for further enhancing the efficiency of PSCs.

Solution-processed Sb2Se3 photocathodes under Se-rich conditions and their photoelectrochemical properties

In this study, selenium (Se)-rich antimony selenide (Sb2Se3) films were fabricated by applying a solution process with the solvents ethylenediamine and 2-mercaptoethanol to optimize the photoelectrochemical (PEC) performance of the Sb2Se3 photocathode. Various antimony (Sb)-Se precursor solutions with different molar ratios of Sb and Se (Sb : Se = 1 : 1.5, 1 : 3, 1 : 4.5, 1 : 7.5, and 1 : 9) were prepared to attain Se-rich fabrication conditions. As a result, the Se-rich Sb2Se3 films fabricated using the Sb-Se precursor solution with a molar ratio of Sb : Se = 1 : 7.5 exhibited an improved PEC performance, compared to the stoichiometric Sb2Se3 film. The charge transport was improved by the abundant Se element and thin selenium oxide (Se2O3) layer in the Se-rich Sb2Se3 film, resulting in a decrease in Se vacancies and substitutional defects. Moreover, the light utilization in the long wavelength region above 800 nm was enhanced by the light-trapping effect because of the nanowire structure in the Se-rich Sb2Se3 film. Hence, the optimal Se-rich Sb2Se3 photocathodes showed an improved photocurrent density of -0.24 mA cm-2 at the hydrogen evolution reaction potential that was three times higher than that of the stoichiometric Sb2Se3 photocathodes (-0.08 mA cm-2).