Fabrication of single-crystal solar cells from phosphorous-doped CdTe wafer

A phosphorous doped CdTe boule was grown from melt using the modified vertical Bridgman technique. Single crystals prepared from the boule showed hole density of (5-10) × 10¹⁵ cm^-3, resistivity ~(10-50) Ω.cm and mobility of ~50 cm²/v.s determined by Hall measurement. The two-photon excitation time-resolved photoluminescence (2PE-TRPL) measurement revealed a bulk minority carrier lifetime of ~47 ns. A 500μm thick single-crystal wafer was prepared and CdS/CdTe heterojunction solar cells were fabricated with ITO/CdS/CdTe/Cu/Au structure where all relevant thin film layers were deposited by DC/RF magnetron sputtering. An efficiency of ~11% and short circuit current density of as high as ~25 mA/cm² has been obtained on a cell upon annealing at 320°C. The high short circuit current density could be attributed to the superior quality of the CdTe material with a relatively longer minority carrier lifetime.