Germanium telluride as a BSF material for high efficiency ultra-thin CdTe solar cell

The polycrystalline cadmium telluride (CdTe) is regarded as one of the leading photovoltaic (PV) materials for its high efficiency and low-cost. The absorber material CdTe has the ideal and direct bandgap of 1.45 eV and it has a high absorption co-efficient over 5×10⁵/cm. In this work, the possibility of ultra-thin absorber layer of CdS/CdTe solar cell was investigated by numerical analysis utilizing AMPS (Analysis of Microelectronic and Photonic Structures) simulator. In the proposed cell, the CdTe layer was reduced and found that 1 μm CdTe layer is enough for acceptable range of cell conversion efficiency. The viability of this ultra-thin CdTe absorber layer was examined, together with 0.1 μm GeTe back surface field (BSF) layer to reduce the barrier height in the valence band and to minimize the recombination losses at the back contact of the CdS/CdTe cell. It was found that the proposed ultra-thin cells have conversion efficiency of 18.68% (Jsc = 21.47 mA/cm², FF = 0.85, Voc = 1.02 V) without BSF and with 100 nm GeTe BSF conversion efficiency increased to 22.53% (Jsc = 24.28 mA/cm², FF = 0.875, Voc = 1.06 V) with only 0.8 μm of CdTe layer. Moreover, it was found that the normalized efficiency of the proposed cells linearly decreased with the increasing operating temperature at the gradient of -0.16%/°C, which indicated better stability of the proposed CdTe solar cell.