The role of interparticle heterogeneities in the selenization pathway of Cu Zn Sn S nanoparticle thin films a real time study

Real time energy dispersive X ray diffraction EDXRD analysis has been utilized to observe the selenization of Cu Zn Sn S nanoparticle films coated from three nanoparticle populations Cu and Sn rich particles roughly 5 nm in size, Zn rich nanoparticles ranging from 10 to 20 nm in diameter, and a mixture of both types of nanoparticles roughly 1 1 by mass , which corresponds to a synthesis recipe yielding CZTSSe solar cells with reported total area efficiencies as high as 7.9 . The EDXRD studies presented herein show that the formation of copper selenide intermediates during the selenization of mixed particle films can be primarily attributed to the small, Cu and Sn rich particles. Moreover, the formation of these copper selenide phases represents the first stage of the CZTSSe grain growth mechanism. The large, Zn rich particles subsequently contribute their composition to form micrometer sized CZTSSe grains. These findings enable further development of a previously proposed selenization pathway to account for the roles of interparticle heterogeneities, which in turn provides a valuable guide for future optimization of processes to synthesize high quality CZTSSe absorber layer

Atomic Scale Structure of Ag,Cu 2 ZnSnSe4 and Cu2Zn Sn,Ge Se 4 Kesterite Thin Films

Kesterite based materials are being researched and developed as affordable, efficient, and mechanically flexible absorber materials for thin film photovoltaics. Both Ag,Cu 2ZnSnSe4 and Cu2Zn Sn,Ge Se4 based devices have shown great potential in overcoming some of the remaining challenges for further increasing the conversion efficiency of kesterite based solar cells. This study therefore investigates the long range crystallographic structure and the local atomic scale structure of technologically relevant thin films by means of grazing incidence X ray diffraction and low temperature X ray absorption spectroscopy. As expected, the unit cell dimensions change about an order of magnitude more than the element specific average bond lengths. In case of Cu2Zn Sn,Ge Se4, the thin film absorbers show a very similar behavior as Cu2Zn Sn,Ge Se4 powder samples previously studied. Small amounts of residual S in the thin films were taken into account in the analysis and the results imply a preferential formation of Sn S bonds instead of Ge S bonds. In Ag,Cu 2ZnSnSe4, the dependence of the Ag Se and Cu Se bond lengths on Ag Ag Cu might indicate an energetic advantage in the formation of certain local configuration

High temperature decomposition of Cu 2 BaSnS 4 with Sn loss reveals newly identified compound Cu2Ba3Sn2S8

The earth abundant quaternary compound Cu2BaSnS4 is being currently studied as a candidate for photovoltaics and as a photocathode for water splitting. However, the chemical stability of this phase during synthesis is unclear. The synthesis of other quaternary tin sulphur based absorbers e.g., Cu2ZnSnS4 involves an annealing step at high temperature under sulphur gas atmosphere, which can lead to decomposition into secondary phases involving Sn loss from the sample. As the presence of secondary phases can be detrimental for device performance, it is crucial to identify secondary phase chemical, structural and optoelectronic properties. Here we used a combination of in situ EDXRD XRF and TEM to identify a decomposition pathway for Cu2BaSnS4. Our study reveals that, while Cu2BaSnS4 remains stable at high sulphur partial pressure, the material decomposes at high temperatures into Cu4BaS3 and the hitherto unknown compound Cu2Ba3Sn2S8 if the synthesis is performed under low partial pressure of sulphur. The presence of Cu4BaS3 in devices could be harmful due to its high conductivity and relatively lower band gap compared to Cu2BaSnS4. The analysis of powder diffraction data reveals that the newly identified compound Cu2Ba3Sn2S8 crystallizes in the cubic system space group I 43d with a lattice parameter of a 14.53 1 . A yellow powder of Cu2Ba3Sn2S8 has been synthesized, exhibiting an absorption onset at 2.19 e

Low Temperature Synthesis of Stable gamma sPbI3 Perovskite Layers for Solar Cells Obtained by High Throughput Experimentation

The structural phases and optoelectronic properties of co evaporated CsPbI3 thin films with a wide range of [CsI] [PbI2] compositional ratios are investigated. We find that for CsI rich growth conditions, CsPbI3 can be synthesized directly at low temperature into the distorted perovskite g CsPbI3 phase with Schottky type defects and without detectable secondary phases. In contrast, PbI2 rich growth conditions are found to lead to the non perovskite d phase. Photoluminescence spectroscopy and optical pump THz probe measurements show carrier lifetimes larger than 75 ns and charge carrier sum mobilities larger 60 cm2 Vs for the g phase, indicating their suitability for high efficiency solar cells. Building on these results p i n type solar cells with a maximum efficiency exceeding 12 and high shelf stability of more than 1200 h are demonstrate

Synergistic Effects of Double Cation Substitution in Solution Processed CZTS Solar Cells with over 10 Efficiency

The performance of many emerging compound semiconductors for thin film solar cells is considerably lower than the Shockley Queisser limit, and one of the main reasons for this is the presence of various deleterious defects. A partial or complete substitution of the cations presents a viable strategy to alter the characteristics of the detrimental defects and defect clusters. Particularly, it is hypothesized that double cation substitution could be a feasible strategy to mitigate the negative effects of different types of defects. In this study, the effects of double cation substitution on pure sulfide Cu2ZnSnS4 CZTS by partially substituting Cu with Ag, and Zn with Cd are explored. A 10.1 total area power conversion efficiency 10.8 activearea efficiency is achieved. The role of Cd, Ag, and Cd Ag substitution is probed using temperature dependent photoluminescence, time resolved photoluminescence, current voltage IV , and external quantum efficiency EQE measurements. It is found that Cd improves the photovoltaic performance by altering the defect characteristics of acceptor states near the valence band, and Ag reduces nonradiative bulk recombination. It is believed that the double cation substitution approach can also be extended to other emerging photovoltaic materials, where defects are the main culprits for low performanc