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To improve the crystallinity and overall film quality of the light absorbing layer is vital to further enhance the performance of sulfide Kesterite Cu2ZnSnS4 (CZTS) solar cells, especially for all solution‐processed devices using ball‐milling processed CZTS that generally leads to poor crystallization. In this work, a novel treatment method involving high‐boiling‐point solvent (HBPS), via simply spinning oleic acid (OA) solution onto CZTS precursor film coupled with an elongated annealing duration, was for the first time reported that enabled not only reduced surface roughness, but considerably increased crystalline of CZTS film. This is corroborated by an enhanced XRD intensity by eight ‐fold in conjunction with a five‐fold increased steady‐state PL intensity, the latter of which also indicates an improved CdZnS/CZTS heterojunction quality. Combined with all solution‐processed buffer layer and contact material, device using HBPS‐treated ball‐milling processed CZTS absorber yielded a power conversion efficiency of 6.1%, which is the highest reported for all solution‐processed pure‐sulfide CZTS solar cells. The HBPS‐treatment approach developed in this work is simple and effective, and in principle can promisingly be applied to any film to work synergistically with thermal annealing treatment, leading to simultaneously enhanced crystallinity and overall film quality while maintaining its planeness. A one‐step high‐boiling‐point solvent treating method is developed to form nearly micron‐sized pure‐sulfide Cu2ZnSnS4 large grains. Oleic Acid is spin‐coated onto CZTS precursor before annealing, combining with extended annealing duration, to enhance crystallinity, enlarge grain size and reduce surface roughness of CZTS film simultaneously. Based on this high‐boiling‐point solvent treatment. all solution‐processed (sputtering‐free) CZTS solar cell achieves competitive photovoltaic performance. [ABSTRACT FROM AUTHOR]

Abstract: In this research, a new route of surface passivation is reported by introducing hydrogen from the atomic layer deposited (ALD) Al2O3 layer into pure sulfide Cu2ZnSnS4 (CZTS) solar cells. Different amounts of hydrogen are incorporated into the Cu2ZnSnS4/CdS interface through controlling the thickness of the ALD‐Al2O3 layer. The device with three cycles of ALD‐Al2O3 yields the highest efficiency of 8.08% (without antireflection coating) with improved open‐circuit voltage of up to 70 mV. With closer examination on the passivation route of ALD‐Al2O3, it is revealed by the surface chemisty study that the Al2O3 can be etched away by ammonium hydroxide in the CdS buffer deposition process. Instead, the hydrogen is detected within a shallow depth from the CZTS surface, and makes a significant difference in the measured distribution of contact potential difference and device performance. This may be interpreted by the effect of hydrogen passivation of the CZTS surface by curing dangling bonds at the surface of CZTS grains. This work may provide a new direction of further improving the performance of kesterite 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]

A 20 nm Ag coating on Mo back contact was adopted to improve the back contact of evaporated Cu2ZnSnS4 (CZTS) solar cells. The Ag layer helped reduce the thickness of MoS2 which improves fill factor (FF) significantly; additionally, it reduced secondary phases ZnS and SnS2−x, which may help carrier transport; it was also involved in the doping of the absorber layer, which compensated the intrinsic p-type doping and therefore drags down the doping level. The doping involvement may enlarge the depletion region and improve lifetime of the absorber, which led to enhancing open circuit voltage (VOC), short circuit current density (JSC), and efficiency significantly. However, it degrades the crystallinity of the material slightly. [ABSTRACT FROM AUTHOR]

The mechanism of crystallization of (CZTS) made by the sulfurization of a sputtered Zn/CuSn stack was studied by transmission electron microscopy. At , the Zn buried at the bottom of the metallic stack was found to be driven to the upper layer by alloying with Cu and reacting with S to form ZnS. At , CZTS was found to be formed and elemental Sn was observed in the vicinity of the back contact region, while large quantities of and ZnS were segregated at the film surface. At , was found, while all the elemental Sn had vanished. Upon extending the duration of the annealing to 10 min, at , all the secondary phases except ZnS were consumed and the CZTS formation was completed, while around 200 nm of was formed between the CZTS layer and Mo back contact. The finished solar cell exhibits an efficiency of 2.66%, an open-circuit voltage of 666.9 mV and a short-circuit current density of . The solar cell performance is possibly limited by the thick layer and the large density of voids in the back contact region due to the Sn loss at high sulfurization temperatures. [ABSTRACT FROM AUTHOR]

Cadmium sulfide (CdS) is the most widely used buffer material for a variety of thin-film solar cells including Cu 2 ZnSnS 4 . However, reports have shown that CdS film obtained by chemical bath deposition (CBD) is not the ideal buffer layer for pure sulfide CZTS solar cell. Zinc doping is a viable approach to modifying the CdS buffer film, but the present methods are far from satisfactory. Here, we innovatively developed an effective way of Zinc doping using partial electrolyte (PE) treatment, resulting in state-of-the-art buffer layer for solar cells based on high-surface-waviness CZTS light absorber. Our study shows that this Zn PE-treated CdS film improved the properties including coverage, full-range light transmittance and conduction band alignment with CZTS. Ultimately, the resultant modified CdS film boosted the open-circuit voltage of our devices by more than 100 mV, yielding power conversion efficiency (PCE) of 3.30%. We note that this is the highest efficiency that has been reported for all solution-processed CZTS solar cells. [ABSTRACT FROM AUTHOR]

In this work we report the Na incorporation from Na-doped Mo (Mo-Na) back contact for kesterite Cu 2 ZnSnS 4 solar cells on flexible stainless steel substrates. It is demonstrated that Na can be effectively incorporated into CZTS by inserting Mo-Na layer at back contact. Direct contact of CZTS and Mo-Na layer leads to poor homogeneity and adhesion. The thickness of MoS 2 formed at the back contact depends on the presence of Na and whether Mo contacts with CZTS directly. Back contact configuration with a Mo capping layer on Mo-Na layer is found to be helpful to maintain the advantages of Mo back contact and control the thickness of MoS 2 interface. As a result, CZTS device fabricated on this configuration yields higher conversion efficiency of 6.2%. However, this efficiency is still far lower than that on traditional soda lime glass substrate which shows efficiency over 8%. The loss mechanism of device fabricated on stainless steel is investigated and analyzed according to the device performance and electrical parameters. [ABSTRACT FROM AUTHOR]

Abstract: A 10nm ZnO layer have been employed as an intermediate layer between absorber and back contact in Cu2ZnSnS4 thin film solar cells prepared by sulfurization of the metallic stacking layers. By introducing this layer, the device conversion efficiency increases from 2.1% up to 3.3%, open-circuit voltage increases from 476mV to 657mV while short-circuit current decreases from 14.52mA/cm2 to 10.72mA/cm2. The ZnO layer can significantly suppress the reaction of Mo back contact with S and facilitate the reaction between S and metallic stacking layers. It results in the MoS2 thickness decrease from 300nm to 80nm and less unreacted elemental Sn left in the CZTS absorber after sulfurization annealing as shown in transmission electron microscopy images. However, due to the Sn loss through a path of SnS at high annealing temperature, the reacted and eliminated elemental Sn results in a higher density of voids formed at the bottom of sulfurized stacking layers. The improvement in the cell efficiency and open-circuit voltage could be related to both reduced MoS2 thickness and removal of shunting path generated by elemental Sn. However, the voids formation at back contact deteriorates the carrier transportation and decreases short-circuit current. [Copyright &y& Elsevier]

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]