Implementing transparent conducting oxides by DC sputtering on ultrathin SiOx / poly-Si passivating contacts

Abstract

This work addresses the development of transparent conductive oxides (TCOs) for Si solar cells featuring SiOx/poly-Si based passivating contacts. Minimizing the thickness of the parasitically absorbing poly-Si layer is essential to reduce losses in the generation of current. However, as the poly-Si shields the critical absorber surface region during the sputter process of an overlying TCO film, the degradation in passivation quality is more severe for poly-Si films below 20 nm. For a thermal annealing of this sputter damage, a trade-off between improved surface passivation and the formation of a transport barrier exists, which needs to be considered for contact engineering. By adjusting the DC sputter process and the subsequent curing procedure, effective passivation recovery of textured samples featuring ultrathin (<15 nm) n-type poly-Si carrier selective layers (iVoc of 735 mV) and a low ρc of 50 mΩcm2 of the c-Si/SiOx/poly-Si/TCO contact could be achieved simultaneously. Combining this process with a highly conductive and broadband transparent cerium and hydrogen co-doped indium oxide film, opens the door for the application of ultrathin poly-Si layers on the front side of silicon solar cells using exclusively industrially established processes.