CZTSSe based thin film solar cells have received considerable interests due to low material cost, suitable band gaps and high absorption coefficient of CZTSSe materials. Achieving high efficiency CZTSSe based thin film solar cells often need a high temperature selenization process that always causes Sn loss in the form of gaseous SnSe2. Additional Sn complement may decrease the loss of Sn during selenization process and improve the performance of fabricated CZTSSe based thin film solar cells. Here, we investigate the effect of additional Sn complement on the performance of CZTSSe based thin film solar cells fabricated from pure element solution. XRD and Raman characterizations indicate that additional Sn complement could reduce the secondary phase that may cause the voltage loss and decrease of efficiency. The solar cell fabricated with 15% additional Sn complement shows the best conversion efficiency of 8.71% (V-oc=0.42 V, J(sc)= 32.73 mA cm(-2), FF=63.19%). To the best of our knowledge, it is the highest efficiency of CZTSSe based thin film solar cells fabricated from pure element solution. Crown Copyright (C) 2016 Published by Elsevier B.V. All rights reserved.