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 SnO 2 :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 ( Φ 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 × 10 −6 –3.18 × 10 −8 ) A cm −2 , series resistances ( R s ) in the range (507–1114) Ω and shunt resistances ( R sh ) in the range (0.84–271) MΩ. The device structures glass/SnO 2 :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 × 10 −8 A cm −2 , equal Φ 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 Ω and 507 Ω and R sh of 197 and 271 MΩ respectively. The device structure with ZnO shows the least performance. Under AM1.5 illumination, the device structure glass/SnO 2 :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.