A new solution-based method to fabricate Cu(2)ZnSn(S,Se)(4) (CZTSSe) thin films is presented. Binary and ternary chalcogenide nanoparticles were synthesized and used as precursors to form CZTSSe thin films. The composition of the CZTSSe films can be easily controlled by adjusting the ratio of the nanoparticles used. The effect of compositional adjustment on device performance is illustrated. Laboratory-scale photovoltaic cells with 8.5% total-area efficiency (or 9.6% active-area efficiency) were demonstrated without anti-reflective coatings. Material characterization data revealed the formation of a bilayer microstructure during thermal processing and suggested a path forward on device improvement.

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Recent studies of n-type semiconductors have demonstrated spin-coherent transport over macroscopic distances, with spin-coherence times exceeding 100 ns; such materials are therefore potentially useful building blocks for spin-polarized electronics ('spintronics'). Spin injection into a semiconductor (a necessary step for spin electronics) has proved difficult; the only successful approach involves classical injection of spins from magnetic semiconductors. Other work has shown that optical excitation can provide a short (<500 ps) non-equilibrium burst of coherent spin transfer across a GaAs/ZnSe interface, but less than 10% of the total spin crosses into the ZnSe layer, leaving long-lived spins trapped in the GaAs layer (ref. 9). Here we report a 'persistent' spin-conduction mode in biased semiconductor heterostructures, in which the sourcing of coherent spin transfer lasts at least 1-2 orders of magnitude longer than in unbiased structures. We use time-resolved Kerr spectroscopy to distinguish several parallel channels of interlayer spin-coherent injection. The relative increase in spin-coherent injection is up to 500% in the biased structures, and up to 4,000% when p-n junctions are used to impose a built-in bias. These experiments reveal promising opportunities for multifunctional spin electronic devices (such as spin transistors that combine memory and logic functions), in which the amplitude and phase of the net spin current are controlled by either electrical or magnetic fields.

Cu 2 ZnSn(S, Se) 4 (CZTSSe) is a promising low-cost and earth-abundant photovoltaic (PV) absorber material.Using binary and ternary chalcogenide nanoparticles as precursors, we have developed a chemical solution route to produce CZTSSe PV devices with the device efficiency as high as 8.8%. The cross-sectional view of the CZTSSe film shows an interesting bilayer microstructure which consists of an upper micrometersized polycrystalline (large-grain) layer and a lower layer with a dense, smooth bottom amorphous (finegrain) morphology. In this paper, we present the composition and properties of the layers and our understanding on the fine-grain layer's impact on the device performance. Based on the observed optoelectronic properties, a numerical model for the CZTSSe-based PV device is developed, and the simulation results show that the fine-grain layer does not affect the device's performance. An experimental design of CZTSSe PV devices with different thicknesses of the fine-grain layers has also confirmed our findings.