Single-Crystal CdTe Homojunction Structures for Solar Cell Applications

We report two different CdTe homojunction solar cell structures. Single-crystal CdTe homojunction solar cells were grown on GaAs single-crystal substrates by metalorganic chemical vapor deposition. Arsenic and iodine were used as dopants for p -type and n -type CdTe, respectively. Another homojunction solar cell structure was fabricated by growing n -type CdTe directly on bulk p -type CdTe single-crystal substrates. The electrical properties of the different layers were characterized by Hall measurements. When arsine was used as arsenic source, the highest hole concentration was ~6 × 10 16 cm –3 and the activation efficiency was ~3%. Very abrupt arsenic doping profiles were observed by secondary ion mass spectrometry. For n -type CdTe with a growth temperature of 250°C and a high Cd/Te ratio the electron concentration was ~4.5 × 10 16 cm –3 . Because of the 300 nm thick n -type CdTe layer, the short circuit current of the solar cell grown on the bulk CdTe substrate was less than 10 mA/cm 2 . The open circuit voltage of the device was 0.86 V. According to a prediction based on measurement of short circuit current density ( J sc ) as a function of open circuit voltage ( V oc ), an open circuit voltage of 0.92 V could be achieved by growing CdTe solar cells on bulk CdTe substrates.