Mössbauer analysis is carried out on CZTS samples, subjected to a low temperature processing at 300 °C (S1) and high temperature processing at 550 °C under sulfur environment (S2). Loss of Sn is observed in sample S2 due to high temperature thermal treatment. The isomer shifts obtained in the Mössbauer spectra confirms the existence of Sn at its 4 + valence state in both the samples. Relatively high quadriple splitting value is observed in S1 with respect to S2, suggesting dislocations and crystal distortion present in S1, which are reduced drastically by high temperature annealed S2 sample. The fabricated solar cell with S1 and S2 absorbers showed significant improvement in efficiency from ∼0.145% to ∼1%. The presence of excess Sn in S1 allows enhanced recombination and the diode ideality factor shows larger value of 4.23 compared to 2.17 in case of S2. The experiments also validate the fact that S1 with Sn rich configuration shows lower acceptor carrier concentration as compared to S2 because of enhanced compensating defects in S1. © 2018 Elsevier B.V.