Efficiency Enhancement of Kesterite Cu2ZnSnS4 Solar Cells via Solution-Processed Ultrathin Tin Oxide Intermediate Layer at Absorber/Buffer Interface

The ultrathin SnO 2 intermediate layer deposited by a successive ionic layer adsorption and reaction (SILAR) method was introduced into the heterointerface between p-type Cu 2 ZnSnS 4 (CZTS) absorber and n-type CdS buffer for interface defect passivation in kesterite thin film solar cells. CZTS solar cells with SnO 2 intermediate layers show higher open circuit voltage ( V oc ) of 657 mV and fill factor ( FF ) of 62.8%, compared to its counterpart cells without the SnO 2 intermediate layer, which have V oc of 638 mV and FF of 52.4%, resulting in improvement in the overall efficiency from 6.82% to 8.47%. The mitigation of the V oc deficit and the improvement of FF are believed to result from the integrated effects of CZTS/CdS heterointerface passivation, shunt blocking, and band alignments. The passivation effect is further affirmed by the improved carrier lifetime. Furthermore, external quantum efficiency profiles show a strengthened blue optical response which is contributed by the decrease of CdS thickness. This work provides a new insight into the CdS/CZTS interface passivation, shunt blocking, and optimization of band alignments, based on solution-processed SnO 2 .