Influence of Copper Composition on Cu2BaSn S,Se 4 Solution Deposited Films and Photovoltaic Devices with Over 5 Efficiency

Cu2BaSn S,Se 4 is currently in the spotlight for prospective environmentally friendly, stable, thin film solar cell application, with demonstrated device power conversion efficiency PCE exceeding 5 for vacuum deposited absorbers. As suggested by first principles calculations, experimental studies involving related Cu2ZnSn S,Se 4 and Cu In,Ga S,Se 2 absorbers prove that the detailed chemical composition typically plays a sensitive role in altering defects and electronic properties of these complicated compound semiconductors. Herein, the copper composition of Cu2BaSn S,Se 4 has been systematically modified, employing a solution based deposition approach, to provide a more complete picture of the phase stability and optoelectronic property sensitivity for this material. X ray diffraction and scanning electron microscopy show that phase purity is preserved over a film Cu content range of nominally 0.94 amp; 8804; [Cu] [Ba Sn] amp; 8804; 1.01. Terahertz spectroscopy and Hall effect measurements reveal that the majority carrier hole density of amp; 8764;1013 cm 3 and mobility amp; 8764;5 cm2 V s , as well as the minority carrier lifetime a bulk lifetime of 180 ps and a surface recombination velocity gt;106 cm s , are nominally independent of Cu content. The champion PCEs exceed 4.7 for all copper compositions in the phase pure region, with a record value of 5.1 , similar to the reported values for record vacuum deposited devices. These results suggest that Cu2BaSn S,Se 4 films and solar cells at the current performance level may be less sensitive to Cu stoichiometry compared to kesterite materials and therefore may provide a more stable material platform to prepare thin film solar cell