An investigation of the influence of different transparent conducting oxide substrates/front contacts on the performance of CdS/CdTe thin-film solar cells

CdS/CdTe/Au thin film solar cells have been fabricated on different transparent conducting oxide (TCO) substrates/front contacts to study the influence of these different TCOs on the performance of the devices. The TCOs used were ZnO, ZnO:Al and SnO2:F. Under dark condition, all three device structures of the type glass/TCO/n-CdS/n-CdTe/Au n-n heterojunction + Schottky barrier, show interesting rectifying behaviors with rectification factors (RF) in the range (10(2.5)-10(5.0)), Schottky barrier heights (I broken vertical bar (B) ) greater than (0.69-0.81) eV, diode ideality factors (n) in the range (1.85-2.12), reverse saturation current densities (J (0) ) in the range (3.18 x 10(-6)-3.18 x 10(-8)) A cm(-2), series resistances (R (s) ) in the range (507-1114) Omega and shunt resistances (R (sh) ) in the range (0.84-271) M Omega. The device structures glass/SnO2:F/n-CdS/n-CdTe/Au and glass/FTO/ZnO:Al/n-CdS/n-CdTe/Au show the best performance with equal J (0) of 3.18 x 10(-8) A cm(-2), equal I broken vertical bar (B) > 0.81 eV, RF of 10(4.9) and 10(5.0), n value of 2.01 and 2.12, R (s) of 615 Omega and 507 Omega and R (sh) of 197 and 271 M Omega respectively. The device structure with ZnO shows the least performance. Under AM1.5 illumination, the device structure glass/SnO2:F/n-CdS/n-CdTe/Au shows the best solar cell performance with open-circuit voltage of 630 mV, short-circuit current density of 23.5 mAcm(-2), fill factor of 0.44 and conversion efficiency of 6.5%, and is followed by the device structure with ZnO:Al showing a conversion efficiency of 6.0%. Suggested energy band diagrams of the devices as well as possible reasons for the observed trends in performance are presented and discussed.