Improved V₂O_X Passivating Contact for p‐Type Crystalline Silicon Solar Cells by Oxygen Vacancy Modulation with a SiO_X Tunnel Layer

Abstract

passivating contacts have achieved a PCE up to 25.11%. [2] However, the a-Si:H involves capital intensive deposition process and toxic gas precursors, [3] and its relatively high parasitic absorption limits further improvements in device performance. [4,5] To address the above issues with lower parasitic absorption and process cost, alternative carrier-selective contacts based on wide bandgap transition metal oxides (TMOs) have triggered extensive research interest in the photovoltaic community. [6] TMOs featuring high work functions (Φ >5.5 eV) such as MoO X , [7][8][9] V 2 O X , [10][11][12] and WO X [13] are capable of inducing either an inversion layer on n-type silicon (n-Si) or an accumulation layer of holes on p-type silicon (p-Si), thus rendering selective hole extraction. [7,14] The c-Si solar cell with a full-area MoO X contact is one of the most successful examples, which has obtained a record PCE of 23.5%. [15] Compared with MoO X , V 2 O X , with properly tuned oxygen vacancies, has a higher work function and can induce a greater upward band bending on the c-Si surface, resulting in a superior fieldeffect passivation quality. [14,16] The highest PCE of n-Si cells with V 2 O X hole transport layer (HTL) is 21.6% up to now. [12] Inmetal oxide (TMO) thin films featuring tunable work function, high transmittance, and simple fabrication process are expected to serve as carrier-selective transport layers for high-efficiency crystalline silicon (c-Si) solar cells. TMOs are prone to reaction or elemental migration with adjacent materials, which leads to uncontrollable optical and electrical properties. In this work, V 2 O X passivating contact, a promising hole transport layer (HTL) thanks to its high work function, is investigated and implemented in p-type c-Si solar cells. An ultrathin SiO X tunnel layer is intentionally introduced by UV/O 3 pretreatment to suppress the redox reaction at c-Si/V 2 O X interface. Both saturation current density and contact resistance are reduced with the presence of UV-SiO X due to the well tunned oxygen vacancies in SiO X and V 2 O X thin films. The power conversion efficiency (PCE) based on p-Si/UV-SiO X /V 2 O X /Ag rear contact achieves 21.01% with an increased open-circuit voltage of 635 mV and fill factor (FF) of 83.25%.

Polymeric Hole‐Selective Contact for Crystalline Silicon Solar Cells

“…Numerous studies have been investigated on the low WF metal oxides (e.g., TiO x , [12] TaO x , [13] MgO x , [14] ZnO, [15] SrO x [16] ), which act as electron-selective contacts (ESCs). Conversely, high WF materials (e.g., MoO x , [17][18][19][20][21][22] VO x , [23] WO x , [24,25] CrO x [26] ) were investigated as hole-selective contacts (HSCs), by inducing an upward band bending that facilitates hole-selective transport. A high efficiency of 23.8% and 22.3% has been achieved on c-Si solar cells featuring a full-area MoO x -based HSC and TiO x N y -based ESC, [27,28] respectively.…”

Stable Dopant-Free Electron-Selective Contact for Silicon Solar Cells

“…Silicon solar cells have witnessed representative high-efficiency technologies such as tunnel oxide passivating contact (TOPCon) and heterojunction with an intrinsic thin layer (HIT), which have demonstrated an efficiency of around 26.81%. − However, the mentioned contacts rely on highly doped regions on the surface of silicon wafers and have severe shortages such as intrinsic energy losses (undesired parasitic absorption of light or c-Si bulk Auger recombination) and manufacturing challenges (costs increase and yield decreases due to complex processes). − Dopant-free carrier-selective contacts offer a potential solution to address these deficiencies. Transition metal oxides like WO x , MoO x , CrO x , and VO x have been verified as degenerate semiconductor characteristics without intended doping and efficient dopant-free hole-selective contacts with ultrahigh work functions (5–6 eV). − “The highest PCE of dopant-free silicon heterojunction (DF-SHJ) solar cells is 23.83%, achieved by using a contact stack with highly hydrogen-diluted (170 sccm) gas mixture of SiH 4 , H 2 , CO 2 , and B 2 H 6 , plasma treatment with boron radicals (PTB), and 1.7 nm MoO x layer as the hole-selective contact” …”

One‐Step Formation of Low Work‐Function, Transparent and Conductive MgFxOy Electron Extraction for Silicon Solar Cells

“…In order to reduce the parasitic absorption caused by the doped amorphous silicon layers, an increasingly popular approach of substituting the doped layers with hole and electron selective materials has been developed as dopant-free silicon solar cells. Wide band gap and high work function (WF) molybdenum oxide (MoO x ), [7][8][9][10][11][12][13][14] tungsten oxide (WO x ), [8][9][10][11][12]14,15] vanadium oxide (VO x ), [8,9,11,12,16,17] and nickel oxide (NiO x ) [8,12,14,18] have been demonstrated as the hole selective contacts. The external quantum efficiency (EQE) responses of these front contacts certify it could promote the short-circuit current density (J sc , gain up to 1 mA cm −2 ) thanks to the lower light parasitic absorption.…”