Modulation of the TCO/MoO_x Front Contact Enables >21% High-Efficiency Dopant-Free Silicon Solar Cells

Abstract

Highly efficient dopant-free silicon solar cell requires effective electron-and hole-selective contacts. We have recently reported a remarkable efficiency of 21.3% for dopant-free silicon solar cells with a low work function and transparent and conductive MgF x O y electron extraction. The transparent conductive oxide (TCO) films and molybdenum oxide (MoO x ) front hole contact also play significant roles in the high efficiency of dopant-free solar cells. In this study, zinc-doped indium oxide (IZO), tin-doped indium oxide (ITO), and titanium-doped indium oxide (ITiO) have been deposited via magnetron sputtering at room temperature. The work function and optoelectrical properties of TCO films and energy band bending together with the MoO x layer are investigated. The impact of this band bending on the photoelectrical performances of devices is analyzed in detail as a function of the MoO x / TCO work function mismatch. The optimized IZO film presents the highest work function (5.21 eV) and conductivity (2140 S/ cm), resulting in reduced barrier height at the MoO x /TCO interface and enhanced hole-selective transport. The light-soaking treatment is introduced to repair the sputtered damage during the IZO deposition. Finally, an impressive cell efficiency of 21.0%, together with V oc , FF, and J sc of 712.4 mV, 76.4%, and 38.6 mA/cm 2 , respectively, shows great potential and provides an effective solution to obtain highly efficient dopant-free silicon solar cells.

Impact of Graphene Monolayer on the Performance of Non-Conventional Silicon Heterojunction Solar Cells with MoOx Hole-Selective Contact

“…However, in this work, the ITO thickness was reduced below 20 nm to investigate graphene as an alternative indium-free transparent electrode. In silicon heterojunction technology, it is known that the electrode work function can significantly impact the band alignment at the corresponding contact [ 37 , 38 , 39 ]. Something similar may be expected for the non-conventional solar cells studied here.…”

Highly Efficient and Highly Flexible Thin Crystalline Silicon Heterojunction Solar Cells Based on Dopant-Free Carrier-Selective Contacts Fabricated with Simple Processes

“…To address these issues, dopant-free electron- and hole-selective contacts (ESCs and HSCs) have been developed to form heterojunctions with c-Si and selectively extract electrons and holes from c-Si while blocking the opposite charges, respectively. − ESCs are mainly low-workfunction materials, e.g., Ca and Mg. − At the metal/c-Si interface, substoichiometric ZnS, TiO x , − MgO x , and SiO x , can be introduced for passivation and substoichiometric LiF x ,,, and MgF x can be applied to lower the interfacial barrier. HSCs are mainly high-workfunction materials, e.g., MoO x , ,,,− WO x , , V 2 O x , ,, NiO x , , Cu 2 O, etc. Hole selectivity can be further boosted by a ultrathin layer of SiO x − or Al 2 O 3 layer inserted between those metal oxides and the c-Si surface.…”