Low Oxygen Content MoO_x and SiO_x Tunnel Layer Based Heterocontacts for Efficient and Stable Crystalline Silicon Solar Cells Approaching 22% Efficiency

Abstract

In crystalline silicon (c‐Si) solar cells, the hole transport layer (HTL) made of high oxygen content MoOx (x > 2.85, H‐MoOx) evaporating from molybdenum trioxide is not ideal due to low optical bandgap and interface reaction effects. This limits the power conversion efficiency (PCE) and stability of c‐Si solar cells. To improve this, low oxygen content MoOx (x < 2.85, L‐MoOx) with a wide bandgap of 3.87 eV, deposited using molybdenum dioxide (MoO2), is explored and implemented. The c‐Si/SiOx (FGA, forming gas annealing)/L‐MoOx heterojunction has a low contact resistivity of ≈15.06 mΩ cm2, which is almost one order of magnitude lower than that of c‐Si/SiOx(FGA)/H‐MoOx heterojunction. Using L‐MoOx as the HTL, a c‐Si solar cell based on the SiOx passivation layer shows a fill factor of 84.38% and PCE of 21.75%, representing the highest efficiency for MoOx‐based p‐type c‐Si solar cells. Scanning transmission electron microscopy results show that the L‐MoOx HTL effectively enhances the stability of c‐Si solar cells when exposed to air by reducing Ag and Si element diffusion into MoOx. This successful preparation of efficient and stable MoOx HTL films, while preserving their field‐effect passivation ability, provides valuable insights into the development of high‐performance HTL.

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.…”

“…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. The p-type organic materials, e.g., poly­(3,4-ethylene dioxythiophene):poly­(styrenesulfonate) (PEDOT:PSS), are often used as HSCs but are inferior to the inorganic counterpart in terms of lifetime.…”