8.3% efficient Cu2ZnSn(S,Se)4 solar cells processed from sodium-containing solution precursors in a closed reactor

Solution-processed Cu-Zn-Sn-S precursors are annealed under reactive Se atmosphere in different reactors in order to investigate the effects on metal composition and morphology. It is possible to minimize metal losses, specifically of Sn, by changing from open reactor to closed graphite reactor. The Cu2ZnSn(S,Se)4 (CZTS,Se) films annealed in the closed reactor exhibit a bi-layer structure with a dense top crust, whereas the other samples are more porous. The densification of the surface and suppression of Sn loss from the sample leads to an increased open circuit-voltage (Voc) = 419 mV for soda lime glass/Mo/CZTSSe/CdS/i-ZnO/ZnO:Al solar cell device. When NaCl is added to the initial precursor solution the device efficiency can be further improved to 8.3% mainly due to an increase in Voc = 450 mV and fill factor = 59%.