Dual Functional Electron-Selective Contacts Based on Silicon Oxide/Magnesium: Tailoring Heterointerface Band Structures while Maintaining Surface Passivation

Silicon (Si)-based dopant-free heterojunction solar cells (SCs) featuring carrier-selective contacts (CSCs) have attracted considerable interest due to the extreme simplifications in their device structure and manufacturing procedure. However, these SCs are limited by the unsatisfactory contact properties on both sides of the junction, and their efficiencies are not comparable with those of commercially available Si SCs. In this report, a high-performance silicon-oxide/magnesium (SiOx/Mg) electron-selective contact (ESC) design is described. Combining an ultrathin SiOx and a low work function Mg layer, the novel ESC simultaneously yields low recombinative and resistive losses. In addition, deposition of Mg on SiOx relaxes the restriction on the threshold thickness of the SiOx for electron tunneling and therefore broadens the optimization space for rear-sided passivation. Meanwhile, hole-selective contact with boosted light harvesting and suppressed interfacial recombination is achieved by forming a fully conformal contact between the conducting poly(3,4-ethylene dioxythiophene): poly(styrenesulfonate) (PEDOT: PSS) and periodic Si pyramid arrays. With the double-sided carrier-selective contact designs, PEDOT: PSS/Si/SiOx/MgSCs with efficiency of 15% are finally obtained via a totally dopant-free processing. Subsequent calculations further indicate a pathway for the improvement of these contacts toward an efficiency that is competitive with conventionally diffused pn junction SCs.