CuSbSe2 thin film solar cells with ~4% conversion efficiency grown by low-temperature pulsed electron deposition

CuSb(S,Se)2 is emerging as an alternative absorber for thin film photovoltaics, for its intrinsic p-type conductivity, tunable energy bandgap (1.0÷1.6 eV), high absorption coefficient > 104 cm-1 and very low cost of the constituent elements. In this work, we studied the structural, compositional and electro-optical properties of CuSbSe2 (CASe) films grown by Low Temperature Pulsed Electron Deposition (LTPED), a developing technology in thin film photovoltaics. We proved that stoichiometric or Cu-poor CASe films can be obtained at low temperature (< 200 °C) from a stoichiometric target with no need for post-deposition treatments to adjust the stoichiometry. Solar cells based on Cu-poor and stoichiometric CASe absorbers exhibit a similar open circuit voltage (~290÷310 mV), while the JSC increases from ~3 mA/cm2 up to ~20 mA/cm2 as the Cu/Sb ratio increases from 0.55 to 0.95. A low FF ~40% still limits the performance of all the cells indicating that the standard architecture of thin film solar cells, currently used for CIGS and CdTe devices, need to be significantly reviewed. The results of the structural and optoelectrical characterization presented in this paper show that JSC, VOC and FF can all be improved as a result of the optimization of the device architecture. The best of the LTPED-grown CASe cells obtained so far, reached an efficiency of 3.8%, very close to the state of the art reported so far in literature.