Performance Evaluation of CuGaO$_{\mathrm{x}}$ Back Buffer Layer in Bifacial CdTe Solar Cells

Since thin-film CdTe device efficiency has reached 22.1{\%}, the next step is to use novel bifacial device configuration to increase energy yield per unit area. Polycrystalline CdTe is affected by interface defects at contacts, and back-contact challenges reduce device performance for back side illumination. Introducing a suitable back buffer layer can yield a positive initial Fermi level offset with the absorber layer. However, deep work function of CdTe (5.7 eV) limits development of a back buffer which can reduce interface defects and improve minority carrier lifetime and device performance for glass and film side illumination. Here, we used spin-coating to synthesize Cu$_{\mathrm{0.3}}$Ga$_{\mathrm{0.7}}$O$_{\mathrm{x}}$, a p-type transparent conductor serving as back-buffer layer for a CdTe cell. For bifacial architecture, these cells were completed with Sn-doped In$_{\mathrm{2}}$O$_{\mathrm{3}}$ (ITO) standard back contact. Time-resolved photoluminescence(TRPL), and current-voltage(J-V) measurements were recorded, and results of thermal stability testing will be reported. Our results showed improved carrier lifetime and device efficiency for cells with Cu$_{\mathrm{0.3}}$Ga$_{\mathrm{0.7}}$O$_{\mathrm{x}}$ back buffer for glass and film side illumination.