Passivating electron‐selective contacts for silicon solar cells based on an a‐Si:H/TiO_x stack and a low work function metal

Abstract

In this work, the ATOM (intrinsic a-Si:H/TiO x /low work function metal) structure is investigated to realize high-performance passivating electron-selective contacts for crystalline silicon solar cells. The absence of a highly doped Si region in this contact structure is meant to reduce the optoelectrical losses. We show that a low contact resistivity (ρ c ) can be obtained by the combined effect of a low work function metal, such as calcium (Φ 2.9 eV), and Fermi-level depinning in the metal-insulator-semiconductor contact structure (where in our case TiO x acts as the insulator on the intrinsic a-Si:H passivating layer). TiO x grown by ALD is effective to achieve not only a low ρ c but also good passivation properties. As an electron contact in silicon heterojunction solar cells, inserting interfacial TiO x at the i-a-Si:H/Ca interface significantly enhances the solar cell conversion efficiency. Consequently, the champion solar cell with the ATOM contact achieves a V OC of 711 mV, FF of 72.9%, J SC of 35.1 mA/cm 2 , and an efficiency of 18.2%. The achievement of a high V OC and reasonable FF without the need for a highly doped Si layer serves as a valuable proof of concept for future developments on passivating electron-selective contacts using this structure.

Recent Advances in and New Perspectives on Crystalline Silicon Solar Cells with Carrier-Selective Passivation Contacts

“…Alternative materials are expected to completely replace doped silicon layers to form the asymmetric carrier selective heterocontacts with c-Si wafers. These alternative materials, which usually are called carrier-selective materials or passivation contact materials, include transition metal oxides [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47], organic materials [48][49][50][51][52][53], and alkali/alkaline earth metals and/or salts [30,40,[54][55][56][57][58][59][60][61]. Compared to doped-silicon layers, dopant-free carrier-selective materials open a wider optical and electrical parameter space, decoupling the optimization of different solar cell loss components.…”

Low Work Function Ytterbium Silicide Contact for Doping-Free Silicon Solar Cells

“…The J0,front of samples with the structure as shown in Figure 2 All ρc values for the electron contact were determined using the two-contact-two-terminal method in order to include all resistive components of the contact in the measured ρc 34,54 . More details on the methods used to determine ρc and J0 can be found elsewhere 34,37,38 .…”

“…For the hole contact, high work function metal oxides, especially MoOx, have been investigated intensively [16][17][18][19][20][21][22] . For the electron contact, low work function metal oxides [23][24][25][26] , metal nitrides 27,28 , rare-earth metal fluorides 29,30 and low work function metals 22,[31][32][33][34][35][36][37][38] have been studied.…”

Simulation of Silicon Heterojunction Solar Cells for High Efficiency with Lithium Fluoride Electron Carrier Selective Layer

“…Wide bandgaps with high work function-based materials, such as molybdenum oxide (MoO x ), vanadium oxide (V 2 O x ), tungsten oxide (WO x ), and nickel oxide (NiO x ), have been proposed as hole transport layers (HTLs) for high efficiency SHJ solar cells [20][21][22][23][24][25]. Similarly, to achieve a high performance for SHJ solar cells, wide bandgaps with low work function-based materials, such as lithium fluoride (LiF x ), magnesium fluoride (MgF x ), titanium oxide (TiO x ), and cesium iodide (CsI), have been proposed as electron transport layers (ETLs) [26][27][28][29][30].…”