Fine‐Tuning the Sn Content in CZTSSe Thin Films to Achieve 10.8% Solar Cell Efficiency from Spray‐Deposited Water–Ethanol‐Based Colloidal Inks

Abstract

Thin film solar cells with Al/ITO/ZnO/CdS/CZTSSe/Mo‐glass structure are fabricated employing a fast and low‐cost preparation procedure using an aqueous ink deposited by nonpyrolytic spray, followed by high temperature crystallization and selenization steps. Capacitance–voltage measurements on previously reported devices with >8% efficiency under 1 sun irradiation show a charge carrier density of the order of 1017 cm−3. Moreover, admittance spectroscopy indicates the presence of mid‐bandgap defects that are tentatively attributed to a Sn deficit in the film. In order to reduce the number of these deep defects within the active layer of our solar cells, the Sn content is tuned in the precursor ink. Their morphology, elemental composition, crystal phases, capacitance–voltage profiling, admittance, photoluminescence, and photovoltaic performances are characterized. The results indicate that tuning the Sn content offers a strong leverage upon some key properties of the active layer, in particular the grain size, and the charge carrier and defect density. By employing this leverage to optimize the performance of our CZTSSe layers, the cell performances are increased to 10.0% without antireflection coating (ARC) and to 10.8% (on 0.25 cm2) with an ARC.

Is the Cu/Zn Disorder the Main Culprit for the Voltage Deficit in Kesterite Solar Cells?

“…[ 15 ] Moreover, Na has been shown to infl uence signifi cantly the number of charge carriers present in the photoactive layer in the dark. [ 49 ] • Lithium impurity may act in a similar way as Na on kesterite grains properties, but was proposed to cause electric fi eld inversion recently evidenced at grain-boundaries.…”

“…[ 15 ] A detailed transport study allowed them to attribute the presence of these detrimental deep defects to the lack of Sn within the kesterite structure. They tentatively incriminated V Sn and/or Cu Sn as the main culprit for the mid gap defects.…”

Green Atmospheric Aqueous Solution Deposition for High Performance Cu2ZnSn(S,Se)4 Thin Film Solar Cells

“…Compared to vacuum deposition method, solution‐processed approach has great advantages in fabrication costs and large‐area deposition (e.g., roll‐to‐roll printing) for thin film photovoltaics (PV) based on CZTSSe absorbers . The most successful CZTSSe thin film PV device to date, fabricated by a hydrazine‐based solution process, has demonstrated a high PCE of over 12% .…”

Study and optimization of alternative MBE‐deposited metallic precursors for highly efficient kesterite CZTSe:Ge solar cells

“…Currently, the certified highest efficiency (12.6%) has been achieved using hydrazine‐based solution approach, although the wide variety of deposition techniques, like coevaporation, sputtering, spray, spin‐coating, or doctor‐blade coating, have also given efficiencies above 10%.…”