A pinhole free Zn(O,S) buffer layer was deposited on CuInSe2 (CIS) absorber by chemical bath deposition (CBD) method. Thin Zn(O,S) exhibits better power conversion efficiency (PCE) at lower thickness. Enhancement of PCE from 1.5% to 3.9% was observed for electrodeposited CIS photovoltaic device when the buffer layer thickness reduces from 50 nm to 20 nm. Although the conduction band offset (CBO) at Zn(O,S)/CIS interface are almost identical for both the 20 nm and 50 nm thick buffer layers, investigation on charge carrier dynamics reveals that the carrier lifetime for the 20 nm buffer is much longer than the 50 nm buffer. This offers a plausible explanation for the higher Tsc of the device with 20 nm buffer layer compared to the device with 50 nm buffer layer. (C) 2015 Elsevier Ltd. All rights reserved.