Application of a Sn4+ doped In2S3 thin film in a CIGS solar cell as a buffer layer

As a Cd-free buffer, In2S3 buffer has been used in Cu(In,Ga)Se2 (CIGS) solar cells. To increase the carrier density of the In2S3 buffer, we doped Sn4+ into the buffer layer, which acted as an electron dopant in the In2S3 buffer layer. It was found that an optimal Sn4+ doping into the In2S3 buffer enhanced the power conversion efficiency of the CIGS solar cell. The deep defect states were reduced at both the bulk and surface of the CIGS solar cell by Sn4+ doping. The capacitance–voltage (C–V) charge density profile showed an increased depletion width in CIGS with the Sn4+ doped In2S3 buffer, thus implying an increase in the electron charge density in the Sn4+ doped In2S3 buffer. At 3% Sn4+ doping into the In2S3 buffer, the power conversion efficiency (PCE) was increased from 10.05% (CIGS solar cell with non-doped In2S3 buffer) to 14.52%.