Silver nanoparticles incorporated in aluminum doped ZnO for heterojunction solar cells

AZO/Si heterojunction solar cells were fabricated and investigated. In this structure AZO plays a role as a transparent current spreading layer and rectifying junction with silicon (Si). Furthermore, by introducing silver nanoparticles (Ag NPs) inside of the AZO film, light harvesting was enhanced because of plasmonic and light scattering effects ensuring minimized electrical and optical loss within the AZO. AZO was grown by co-sputtering of ZnO and Al. AZO (Al 5.78 wt%) was deposited on Si with 20, 40 nm of thickness. Ag NPs were then spread by spin coating and 230 nm of AZO was deposited again having a sandwich-like structure. In SEM observation, Ag NPs covered 4.7 % of the front surface. Solar cells were fabricated using Al front and back contacts with the size of 0.25 cm². Computer simulations were carried out to optimize current gain regarding a total photon energy into Si. In calculation, absorption enhancement is maximized when Ag NPs are located as close to the Si layer in the range of 10 ~ 40 nm. Experimentally, 20 nm of bottom AZO showed the best result in terms of efficiency. Spectral response showed 15 % enhancement at 430 nm and 5 ~ 10% enhancement within 600 ~ 1000 nm. Best performance was shown to have 0.36 V of V_oc, 28.3 mA/cm² of J_sc and an efficiency of 5.91 %.