Atomic layer deposition of In_2O_3 transparent conductive oxide layers for application in Cu(In,Ga)Se_2 solar cells with different buffer layers

摘要

This contribution presents the development of atomic layer deposited (ALD) In_2O_3 films for utilization as transparent conductive oxide (TCO) layers in Cu(In,Ga)Se_2 (CIGSe) solar cells. The effects of ALD process parameters on the morphology and growth of In_2O_3 are studied and related to the electrical and optical properties of the films. Maintaining similar resistivity values compared to commonly used ZnO:Al (AZO) TCOs (ρ = (5-7) × 10~(-4) Ωcm), a superior mobility of μ ≈ 110cm~2/Vs could be achieved (more than five times higher than a ZnO:Al reference), which results in a significantly reduced parasitic optical absorption in the infrared region. Application of the optimized In_2O_3 layers in CIGSe solar cells with varying buffer layers (CdS and Zr_(1-x)Sn_xO_y (ZTO)) leads to a distinct improvement in short circuit current density J_(sc) in both cases. While for solar cells containing the ZTO/In_2O_3 window structure, a drop in open-circuit voltage V_(oc) and a deterioration under illumination is observed, the TCO exchange (from AZO to In_2O_3) on CdS buffer layers results in an increase in V_(oc) without detectable light bias degradation. The efficiency η of the best corresponding solar cells could be improved by about 1% absolute.