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

Abstract

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%.