Meijun Lu

A simple solution-based route to high-efficiency CZTSSe thin-film solar cells

Solution-based Cu2ZnSn(S,Se)4 (CZTSSe) thin film deposition routes focusing on chemistries with attractive scalability and handling characteristics, while delivering high efficiency devices are promising technologies for low-cost solar cells. In this paper we describe a new approach for the fabrication of CZTSSe thin films using inks comprised of mixtures of binary and ternary metal-chalcogenide nanocrystals dispersed in simple organic solvents. The resulting blended inks can be coated under ambient conditions to give precursor films which are in turn converted to device-quality CZTSSe absorbers via thermal annealing in a selenium atmosphere. Using this approach we have demonstrated CZTSSe solar cells with total area efficiencies in excess of 8.5% (or 9.6% per active area) under 1 Sun AM1.5 illumination.

Characterization and understanding of performance losses in a highly efficient solution-processed CZTSSe thin-film solar cell

We present results on the characterization of a highly efficient CZTSSe solar cell fabricated using a solution-based process, aiming to gain a better understanding of its efficiency-limiting causes. Under red light illumination, we observed a red-kink in the current-density versus voltage (J-V) curve, likely due to a persistent photoconductivity in the buffer layer. Temperature-dependent J-V analysis suggests that interface recombination is the dominant loss mechanism. Defect analysis using admittance spectroscopy (AS) shows a single bulk defect level at ~63 meV and may be attributed to copper vacancy (VCu). The carrier concentration of the device determined using drive-level capacitance profiling (DLCP) is ~2.5×1016 cm-3.

Cu 2 ZnSn(S, Se) 4 thin-film photovoltaic devices using non-vacuum based processing

Large-scale deployment of currently favored high-efficiency, thin-film photovoltaic materials (e.g., CdTe, CIGS) may be resource-limited due to dependence upon relatively non-abundant elements (e.g., In, Ga, Te). As a result, Cu2ZnSn(S, Se)4 (CZTSSe), with its reliance upon low-cost, earth-abundant elements, is attracting attention as an alternative candidate material for use in thin-film photovoltaic devices. In this paper, we will introduce our efforts to develop scalable routes to the low-cost, non-vacuum based construction of CZTSSe solar cells. While we have been pursuing a variety of types of precursors to CZTSSe, we will limit our results here to results derived from quaternary CZTS nanoparticles. We will focus on the processing of the CZTSSe thin films and in particular upon the effects of different annealing atmospheres. Structural and optical characterization of the resulting CZTSSe films, and the corresponding PV device performance will be presented.