High performance intermediate-band solar cells based on ZnTe:Cr with ZnO:Al electron transport layer

Abstract

An intermediated-band in Cr-doped ZnTe (ZnTe:Cr) thin films was analyzed and high performance intermediate-band solar cells (IBSCs) were fabricated with a high-quality ZnO:Al electron transport layer (ETL). The energy band structure and defect states of the ZnTe:Cr absorber layer by means of ultraviolet photoelectron spectroscopy and deep level transient spectroscopy were investigated, and then two defect levels, L2 and L4, are positioned 0.3 and 1.14 eV above the valence band. Especially, it was confirmed that the 1.14 eV activation energy of the L4 defects corresponds to the energy required to reduce Cr+ to Cr2+ , which these defects are responsible for the intermediate band observed in the ZnTe:Cr thin film. From the optical and electrical measurements, the ZnO:Al thin film grown under the partial oxygen pressure (p(O-2)) of 1 mTorr show high mobility, low resistivity, and few antisite oxygens defects. Finally, the ZnTe:Cr IBSC with ETL of ZnO:Al grown under 1 mTorr p(O-2) showed photoelectric power conversion efficiency of 8.13%.