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Antimony sulfide is an emerging 1D nontoxic Earth‐abundant photovoltaic material with favorable wide bandgap as a suitable top‐cell candidate for multijunction tandem solar cells. However, the current fabrication technology for Sb2S3 solar cells relies heavily on a high‐purity Sb2S3 source, which limits its large‐scale deployment. Therefore, it is attractive to fabricate the Sb2S3 solar cells directly from the raw stibnite source, which can be cost effective by avoiding the complicated, costly purification and refinement process of the stibnite ore, while reducing process‐emitted pollution. Herein, high‐quality Sb2S3 films (thickness: ≈1 μm) by the vapor transport deposition of raw stibnite ore powder are obtained, followed by a sulfurization process to remove the surface oxides and facilitate alkali element redistribution. In this way, the particle size is increased from ≈500 nm to ≈1.5 μm, the carrier concentration of the Sb2S3 film is increased from ≈1015 to ≈1016 cm−3, and the power conversion efficiency of Sb2S3 solar cell is increased by more than two times. Through the elemental distribution analysis, it is found that it is the redistribution of alkali elements introduced from the natural stibnite ore that induces the grain growth, contributes toward defect suppression, and leads toward enhanced device performance. [ABSTRACT FROM AUTHOR]

The anomalous optoelectronic properties of a quasi‐vertical orientated Chalcostibite CuSbS2 thin film synthesized on glass substrate are studied in detail. Two well‐separated absorption edges of CuSbS2 are identified by photothermal‐deflection spectroscopy (PDS) at 1.48 and 0.90 eV. The formation mechanism of the 0.9 eV infrared edge is found to be crystal orientation related. The properties of the 0.9 eV absorption edge are subject to detailed investigation using temperature‐dependent photoluminescence (TDPL) characterization, which attribute the origin of this phenomenon to a deep‐level defect state near the mid‐bandgap of CuSbS2. [ABSTRACT FROM AUTHOR]

Environmentally friendly and earth abundant Cu2ZnSnS4 (CZTS) based thin films are potential absorbers for next generation photovoltaics. Their optical properties provide the option to be used as upper cells for Si based tandem solar cells, together with a similar structure to Si, triggering interest in investigation of CZTS/Si tandem cells. However, epitaxially growing CZTS on Si can be challenging. Here, we heteroepitaxially grow tetragonal Cu2ZnSnS4 (CZTS) thin films on single crystalline cubic Si (111) wafers with a 4° miscut by simple and low-cost radio frequency magnetron sputtering from a single target. The CZTS film displays a mirror-like surface with a surface roughness of 8.46 nm. The absorption coefficients of the epitaxial CZTS are over 104 cm−1 at 1.5 eV and 1.0 × 105 cm−1 at 2.1 eV. The bandgap is 1.45 eV, and the photoluminescence lifetime is 7.04 ns. Our results demonstrate the potential of the epitaxial CZTS films fabricated by sputtering on the Si substrate for application in CZTS/Si based tandem solar cells. [ABSTRACT FROM AUTHOR]

Abstract: The thin‐film photovoltaic material Cu2ZnSnS4 (CZTS) has drawn worldwide attention in recent years due to its earth‐abundant, nontoxic element constitution, and remarkable photovoltaic performance. Although state‐of‐the‐art power conversion efficiency is achieved by hydrazine‐based methods, effort to fabricate such devices in a high throughput, environmental‐friendly way is still highlydesired. Here a hydrazine‐free all‐solution‐processed CZTS solar cell with Na2S self‐depleted back contact modification layer for the first time is demonstrated, using a ball‐milled CZTS as light absorber, low‐temperature solution‐processed ZnO electron‐transport layer as well as silver‐nanowire transparent electrode. The inserting of Na2S self‐depleted layer is proven to effectively stabilize the CZTS/Mo interface by eliminating a detrimental phase segregation reaction between CZTS and Mo‐coated soda lime glass, thus leading to a better crystallinity of CZTS light absorbing layer, enhanced carrier transportation at CZTS/Mo interface as well as a smaller series resistance. Furthermore, the self‐depletion feature of the Na2S modification layer also averts hole‐transportation barrier within the devices. The results show the vital importance of interfacial engineering for these CZST devices and the Na2S interface layer can be extended to other optoelectronic devices using Mo contact. [ABSTRACT FROM AUTHOR]

In this work, epitaxial Cu2ZnSnS4 (CZTS) films grown by magnetron sputtering were annealed by continuous wavelength diode laser as an alternative post-deposition heat treatment replacing conventional post-annealing within sulfur atmosphere to improve the film quality. Upon ultrafast millisecond diode laser annealing, improvement of crystallinity and reduction of Cu/Zn disordering were observed in the CZTS thin films. The results indicate that the diode laser treatment can enable fast, effective, and efficient annealing of CZTS thin films. [ABSTRACT FROM AUTHOR]

The effects of an ultrathin ZnO intermediate layer deposited at the CZTS/Mo interface on CZTS solar cell performance have been investigated in this work. The ZnO layer inhibits the generation of MoS2 layer and the formation of voids in the CZTS absorber. Consequently, the incorporation of this layer reduces the series resistance and increases the shunt resistance, which boosts photovoltaic conversion efficiency from 1.13% to 4.3%. (© 2014 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Heteroepitaxial growth of kesterite Cu2ZnSnS4 (CZTS) thin film on cubic ZnS(100) single crystal substrate was achieved by radio frequency magnetron sputtering from a single CZTS target. An optimal substrate temperature in the range of 470-500 °C is found suitable for this epitaxial growth. The growth of CZTS was confirmed to be along a-axis. The sputtered CZTS thin film is homogeneous throughout the whole film. The band gap of the film is found to be approximately 1.51 eV, i.e., promising for high efficiency thin film solar cells. [ABSTRACT FROM AUTHOR]

Aluminium-assisted crystallization is used to grow single-crystalline SixGe1−x film epitaxially on Si substrate at a relatively low temperature (350–450°C). Investigation of the mechanism by which Al film causes epitaxial growth of SixGe1−x suggests a four-step growth process is involved. The composition of the SixGe1−x film can be controlled by the annealing conditions. This SixGe1−x film can be used as a buffer layer for the epitaxial growth of Ge on Si or as a virtual substrate for the fabrication of III–V devices. [ABSTRACT FROM AUTHOR]

an important step towards the realisation of silicon-based tandem solar cells using silicon quantum dots embedded in a silicon dioxide (SiO) matrix, single-junction silicon quantum dot (Si QD) solar cells on quartz substrates have been fabricated. The total thickness of the solar cell material is 420 nm. The cells contain 4 nm diameter Si quantum dots. The impacts of post-metallisation treatments such as phosphoric acid (HPO) etching, nitrogen (N) gas anneal and forming gas (Ar: H) anneal on the cells' electrical and photovoltaic properties are investigated. The Si QD solar cells studied in this work have achieved an open circuit voltage of 410 mV after various processes. Parameters extracted from dark I- V, light I- V and circular transfer length measurement (CTLM) suggest limiting mechanism in the Si QD solar cell operation and possible approaches for further improvement. [ABSTRACT FROM AUTHOR]

Understanding the elemental composition and point defect properties is crucial for improving device performance in Chalcogenide thin film solar cells. The correlation between composition and defect characteristics of CuSbS 2 thin film sulfurized from metallic precursors was systematically investigated. Interestingly, it was found that CuSbS 2 polycrystalline thin film maintains an overall Cu-rich composition with a Cu/Sb ratio greater than 1, regardless of the initial precursor compositions. Besides, no obvious difference in the performance of integrated devices is observed, due to the similar Cu/Sb atomic ratios and electronic properties (carrier concentration and mobility) in these CuSbS 2 thin films. By conducting admittance spectroscopy analysis on CuSbS 2 devices, identical defect energy was obtained at 280 meV above the valence band maximum, which can be ascribed to Cu Sb. This could be mainly explained by the Cu-rich composition induced low formation energy of Cu Sb. Therefore, further defects engineering focusing on Cu Sb is required to boost the device efficiency of CuSbS 2 solar cells. • The correlation between composition and defect characteristics has been systematically studied in CuSbS 2 solar cells. • Polycrystalline CuSbS 2 thin-films exhibit a Cu-rich composition across a wide range of initial precursor compositions. • Polycrystalline CuSbS 2 shows consistent Cu/Sb ratios and electronic properties, regardless of precursor compositions. • Cu Sb is revealed to be the dominant defect in Cu-rich CuSbS 2 thin-film prepared by the co-sputtering method. [ABSTRACT FROM AUTHOR]

Abstract: Properties of heavily boron-doped hydrogenated polycrystalline germanium (Ge) films sputter-deposited on glass are investigated for developing p+ emitters of the bottom cells of low cost monolithic tandem solar cells. The films were deposited and in-situ doped by co-sputtering Ge with boron at various power levels (P B) in a mixture of argon and hydrogen at 500°C, and then followed by a rapid thermal anneal process at 550°C for 120s or 600°C for 60s, respectively. The dependence of the structural properties of the films on the various boron incorporations as well as annealing conditions was explored by Raman and X-ray diffraction measurements. We find that the films as deposited at 500°C are polycrystalline with strong (220) preferential orientation, which are normally of columnar structure, confirmed by cross-sectional transmission electron microscopy. Revealed by Hall measurements, a boron activation level of 6.24×1019 atoms/cm3, well above reported maximum solid solubility in crystalline Ge, was obtained in the as deposited film at P B=55W. Annealing at 600°C enhanced the concentration to 1.21×1020 atoms/cm3. A fact that boron hardly diffuses in Ge at temperatures below 800°C makes the resultant material an excellent candidate for thin p+ emitters of the bottom cells of monolithic tandem solar cells. [ABSTRACT FROM AUTHOR]

Abstract: Hydrogenated polycrystalline Si x Ge1−x films, with a varying silicon fraction x ≤0.246, were in situ deposited in an argon and hydrogen mixture at 500°C using radio frequency sputtering with an aim to develop a material for the bottom cell of a low cost monolithic tandem solar cell. Silicon and germanium atomic compositions of the films were determined by X-ray photoelectron spectroscopy (XPS). Structural evolution revealed by Raman and X-ray diffraction (XRD) indicated that the crystallinity of the films was improved with decreasing silicon fraction, accompanied with an increase of surface roughness verified by atomic force microscopy (AFM). Optical band gaps of these films derived from Tauc plots, which were calculated from reflectance/transmittance measurements, decreased with decreasing silicon fraction. Resistivity of the films, determined by four-point-probe technique, significantly decreased as well. High quality with low thermal budget obtained in this work suggests the films could be used in thin film solar cells on glass. [ABSTRACT FROM AUTHOR]

• Preparation of CZTS thin films via facile and environmentally friendly SILAR method. • Analysis of the effects of different annealing temperature and holding time on film quality. • Fabrication of 4.26% efficiency solar cells by water-based inorganic method. Kesterite Cu 2 ZnSnS 4 (CZTS) solar cells are regarded as a promising photovoltaic technology owing to the non-toxic and earth-abundant constitutes. With the application of scalable and low-cost solution methods, the possibility of its commercialization can be further increased. This work explores preparing prominent CZTS films by an economically feasible successive ionic adsorption and reaction (SILAR) synthesis method. The obtained precursor with the Mo/ZnS/Cu 2 SnS 3 structure requires appropriate substantial annealing under a chalcogen atmosphere to form kesterite CZTS films. The annealing process is therefore optimized to improve the film quality and the performance of solar cells. Specifically, the optimal annealing condition is determined by adjusting the annealing temperature and holding time, respectively. The CZTS film annealed at 580 °C for 60 min demonstrates better film quality in terms of surface morphology, crystallinity, and phase purity. Consequently, CZTS solar cells fabricated with the optimal absorber exhibit a preferable efficiency of up to 4.26%. [ABSTRACT FROM AUTHOR]

This review summarizes some emerging inorganic photovoltaic materials including Cu(In,Ga)Se 2 (CIGSe), kesterite Cu 2 ZnSn(S,Se) 4 (CZTSSe), CdTe, Sb 2 Se 3 and inorganic perovskite CsPb(I 1− x Br x) 3. The materials features, development history and performance enhancements for each of solar cells are discussed in detail. The efficient conversion of solar energy to electricity for human utilization heavily relies on the development of solar cells. Nowadays, a variety of high-performance solar cells are constantly emerging. Thin-film solar cells made from inorganic materials have constituted one of the major categories of solar cells showing potential in the fast growing photovoltaic (PV) market. In order to provide an overall grasp of and insight into the future direction of inorganic thin-film solar cell development, we review key emerging and representative inorganic photovoltaic materials including chalcopyrite Cu(In,Ga)Se 2 (CIGSe), kesterite Cu 2 ZnSn(S,Se) 4 (CZTSSe), CdTe, Sb 2 Se 3 and inorganic perovskite CsPb(I 1− x Br x) 3 in this paper. Absorber materials, evolution of device development, and current challenges and key strategies for performance enhancement are detailed. [ABSTRACT FROM AUTHOR]

Highlights • Cu 2 ZnSnS 4 thin films are fabricated on Si substrates by one-step sputtering. • Cu 2 ZnSnS 4 solar cells on Si with photovoltaic response are fabricated. • The interactions between Cu 2 ZnSnS 4 and Si are studied. Abstract Integrating commercialized Si solar cells with eco-friendly and earth-abundant Cu 2 ZnSnS 4 (CZTS) film is a promising method to increase power conversion efficiency and hence reduce the levelized cost of electricity. However, synthesis of CZTS thin film on Si as well as the study of the interaction between the two materials, which are crucial for good performance of CZTS/Si two-terminal devices, are areas that have been less investigated. Here, we grow polycrystalline CZTS thin films on Si (1 0 0) substrate by sputtering and study the properties of the CZTS thin film and interface between the CZTS and Si. The CZTS shows uniform microstructure and optimal optical properties. A CZTS solar cell which is fabricated on Si shows a photovoltaic response although subjected to high serious resistance, and Cu diffusion was found from CZTS into Si, which caused needle-like dislocations in Si. Therefore, an effective conductive barrier layer between CZTS and Si is desirable to inhibit Cu from diffusing into Si for tandem solar cell purposes. The study offers valuable input for understanding the properties of CZTS thin film sputtered from single target sputtering and the impact on the interfaces and underlying Si, suggesting concerns that manufacturers need to be aware of for its application in tandem solar cells based on Si. [ABSTRACT FROM AUTHOR]

Short minority carrier lifetime and low open circuit voltage (Voc) are key issues limiting the current efficiency development for Cu 2 ZnSnS 4 (CZTS) thin film solar cells. This work presents the use of Cd ion soaking and post-heat treatment to increase the lifetime and Voc of CZTS. The time-resolved photoluminescence (TRPL) results confirmed that Cd ion soaking and post heat treatment is effective in enhancing the minority lifetime, from ∼10 ns up to ∼28 ns. With analyses of the current density- voltage (J-V) curves and external quantum efficiency (EQE) data, Cd ion soaking and subsequent post heat treatment is found to greatly reduce the recombination and improve the junction quality, contributing to a ∼70 mV Voc enhancement and resulting in the increased device efficiency of 7.6%, from 5.9%. [ABSTRACT FROM AUTHOR]

Kesterite Cu 2 ZnSnS 4 (CZTS) thin film solar cells are fabricated based on sputtering and post sulfurization process on stainless steel substrates. NaF layers with different thickness are used as external sodium source to address the lack of Na issue in Na-free steel substrates and 10 nm of NaF layer is proved to be the optimal thickness. Sodium incorporation into CZTS induces the metal element redistribution, facilitates CZTS film recrystallization and promotes the phase evolution. Appropriate amount of sodium is evidenced to yield an enhancement in power conversion efficiency from 3.07% to 4.10% whilst further increase in sodium tends to deteriorate the device efficiency. Device performance deterioration is correlated to the rather small grain size accompanied with a large amount of grain boundaries and unfavorable SnS 2 secondary phase for CZTS samples without sodium, while pinholes and lower carrier density in absorber for CZTS samples with over amount of sodium. [ABSTRACT FROM AUTHOR]

Film uniformity and large crystalline size are indispensable and critical for obtaining high performance planar perovskite solar cells. Perovskite precursor composition plays a key role in the formation of high quality perovskite films. In this work, excess PbCl 2 is deliberately introduced, and is found to facilitate the solubility of CH 3 NH 3 I in concentrated solution at room temperature. The excess PbCl 2 is found to alter the formation pathway of perovskite thin films. Accordingly, the formation pathway is proposed. Analysis of the perovskite films and associated devices revealed that extremely uniform perovskite films consisting of large grains of several microns can be obtained with a small amount of excess PbCl 2 . The associated planar perovskite solar cells showed a reliable and reproducible efficiency of 16.1%. [ABSTRACT FROM AUTHOR]

Recently, Ag incorporation into Cu(In,Ga)Se 2 structure was found to benefit the solar cell performance. However, (Ag,Cu) 2 ZnSnS 4 used as the solar cell absorber is not widely reported even though Ag 2 ZnSnS 4 has shown much better photocatalysts activity for H 2 evolution than Cu 2 ZnSnS 4 . In this paper, (Ag,Cu) 2 ZnSnS 4 thin film solar cell was synthesized through sulfurization of Ag/Zn/Cu/Sn metallic stacked layers. In order to understand the actual role of Ag in the Cu 2 ZnSnS 4 structure, the changing chemical environment, microstructure and intragrain defect due to the Ag incorporation, were studied by X-ray photoelectron spectroscopy and transmission electron microscopy. After sulfurization, Ag is uniformly distributed in the absorber and is incorporated into Cu 2 ZnSnS 4 crystal structure but no obvious change of the Cu 2 ZnSnS 4 chemical environment is detected. A large density of voids is formed at the Cu 2 ZnSnS 4 /Mo interface and some of these voids are found to be coated with CdS which is believed to be detrimental to Cu 2 ZnSnS 4 device performance. In contrast, Ag incorporation reduces the size and amount of voids and thus effectively eliminates CdS deposited at back contact region. Moreover, fewer planar defects and Cu vacancies are formed in the (Ag,Cu) 2 ZnSnS 4 sample than Cu 2 ZnSnS 4 sample as suggested by electron diffraction patterns. Therefore, improved solar cell performance should result from the formation of (Ag,Cu) 2 ZnSnS 4 structure. [ABSTRACT FROM AUTHOR]

Abstract: An industry compatible annealing method-rapid thermal annealing (RTA) of Mo coated soda lime glass substrate has been investigated to improve evaporated Cu2ZnSnS4 (CZTS) thin film solar cell efficiency. It indicates that the RTA treatment makes the Mo film dense, facilitates the column growth of the Mo film and the growth of the CZTS absorber though it enhances the formation of voids and secondary phases in the meantime. Also, this treatment causes low absorption of the absorber. Consequently, the treatment enhances open circuit voltage (V OC) as well as efficiency dramatically, improves fill factor (FF) mildly; though lowers the short circuit current density (J SC) slightly. [Copyright &y& Elsevier]

Abstract: Tandem PV cells – with their increased efficiency due to a multi-band gap approach – usually involve expensive materials and fabrication. Thin film approaches, with an engineered variation in band gap through the use of quantum confinement in Si quantum dots, offer a cheaper alternative. Presented are characterisation and modelling data on fabrication of such Si and Sn QD nanostructures in various dielectric matrices by self-organised thin film deposition, with demonstrated confined energy levels of 1.7 eV for 2 nm diameter QDs. This being the optimum energy for an upper tandem cell element. [Copyright &y& Elsevier]

• Cu 2 SrSnS 4 (CSTS) thin films synthesized via a sol-gel based solution process. • Morphological, phases and optical properties of CSTS thin films characterized. • 600°C annealing and Sr/Sn atomic ratios of 1.15 were the best preparation conditions. • Champion CSTS solar cell with 0.164% power conversion efficiency obtained. • Feasibility of solar energy harvesting of CSTS material demonstrated. According to theory calculation, the Cu 2 SrSnS 4 (CSTS) become a candidate material for harvesting solar energy via either photovoltaic (PV) or photoelectrochemical (PEC) paths due to its efficient light-absorbing capability (high absorption coefficients above 104 cm−1), earth-abundant, nontoxic constituents, and suitable defect properties. As a new material, there is a long way to accomplish the application of CSTS. Film preparation of CSTS are very critical. In this work, CSTS thin films were synthesized by a sol-gel based solution process. The obtained CSTS films showed trigonal structure with band gap of 1.93 eV and p-type conductivity. By comparing the CSTS thin films synthesized with different annealed temperature and Sr/Sn atomic ratios, we confirmed that sulfurization annealing at 600°C and Sr/Sn atomic ratios of 1.15 yields relatively high quality CSTS films. A PEC cell using the CSTS thin film as working electrode were established and a saturated photocurrent of ∼0.5 mA/cm2 had been achieved. It has also been applied to a PV device, demonstrating open-circuit voltage of 296 mV and power conversion efficiency of 0.164%. Pinholes in the films and reef-like grains at the surface of CSTS films were likely to limit the devices performance. The feasibility of solar energy harvesting of CSTS material was demonstrated. [ABSTRACT FROM AUTHOR]