Investigation of MoO_x/n‐Si strong inversion layer interfaces via dopant‐free heterocontact

Abstract

Transition metal oxides (TMOs)/silicon (Si) heterocontact solar cells are currently under intensive investigation due to their simple fabrication process and less parasitic light absorption compared to traditional heterocontact counterparts. Effective segregation of carriers which is related to carrier‐selective heterocontact is crucial for the performance of photovoltaic devices. Molybdenum oxide (MoOx, x ≤ 3), with a wide bandgap of ∼3.24 eV as well as defect bands derived from oxygen vacancies located inside the band gap, has been introduced to integrate with n‐type Si (n‐Si) as hole selective contact. Here, we utilize a stepwise in situ deposition of MoOx to investigate its interaction with Si by X‐ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) measurements. A strong inversion layer originating from a charge transfer process is demonstrated in the n‐Si surface region upon MoOx contact characterized by XPS, UPS, capacitance–voltage (C–V), and minority charge carrier lifetime mapping measurements. A dopant‐free heterocontact is built within n‐Si with a high built‐in potential (Vbi) of ∼0.80 V which benefits for acquiring a high open circuit voltage (Voc). These results give a detailed interpretation on the carrier transport mechanism of MoOx/n‐Si heterocontact and also pave a new route toward fabricating high efficiency, low‐cost solar cells.

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

“…ZnO has a very similar band structure as TiO 2 , although ZnO cannot form similar bonds and does not play a role in the passivation. Finally, when TiO 2 was used as an electron-selective contact, the corresponding solar cell demonstrated a V oc of 643 mV and FF of 72.4%, while a V oc of 637 mV and FF of 75.2% were obtained for the ZnO electron-selective contact [82]. Ye and Gao's group directly deposited titanium film on an n-type c-Si of 8 Ω•cm by electron beam evaporation, which was then annealed at 250 • C in an oxygen atmosphere to form TiO 2 .…”

“…Sun compared the difference between the heterojunction, formed by ZnO/c-Si and TiO 2 /c-Si. The TiO 2 not only realize the electron selectivity, but also passivate the c-Si surface [82], which can contribute to the formation of Si-O-Ti bonds. ZnO has a very similar band structure as TiO 2 , although ZnO cannot form similar bonds and does not play a role in the passivation.…”

Simulation of an efficient silicon heterostructure solar cell concept featuring molybdenum oxide carrier-selective contact

“…Choosing the dopant‐free TMO material, as a potential alternative of doped a‐Si:H, with an appropriate work function allows effective blocking of electron minority charge carriers. Among these investigated materials, molybdenum oxide (MoO x , x < 3) is emerging as a superior hole transport layer that exhibits excellent carrier‐selective properties owing to its higher band gap of 3.24 eV and correspondingly higher work function of ~6.9 eV . So far, MoO x ‐based CSC solar cell has yielded a record η of 22.5% that features MoO x /i‐a‐Si:H as a hole selective window and passivation stack along with i‐aSi:H/n‐a‐Si:H back surface field and passivation stack layers .…”

“…Among these investigated materials, molybdenum oxide (MoO x , x < 3) is emerging as a superior hole transport layer that exhibits excellent carrier-selective properties owing to its higher band gap of 3.24 eV and correspondingly higher work function of 6.9 eV. 17,19,[26][27][28] So far, MoO x -based CSC solar cell has yielded a record η of 22.5% that features MoO x /i-a-Si:H as a hole selective window and passivation stack along with i-aSi:H/n-a-Si:H back surface field and passivation stack layers. 23 Coupled with offering improved optical transmittance with smaller thickness, 29 MoO x is an ideal candidate to be integrated with SHJ technology as a window layer since it eliminates the need for depositing doped a-Si:H by using poisonous gases within the plasmaenhanced chemical vapour deposition system.…”

Improving the Passivation Stability of a Polymer Thin Film on Si by the Introduction of MoO3 Nanoparticles Into the Polymer Matrix

“…The problem above could be solved by increasing the Ф of PSS to a value greater than the electron affinity of the bulk Si (Figure (b) and (d)). MoO 3 is one of the most promising materials for this application due to its high Ф of 4.9–6.8 eV, and this material has attracted extensive interest in several solar cells and organic light emitting diodes . In this work, we add MoO 3 nanoparticles into a PSS matrix to form PSS:MoO 3 (PSSMO) composite films.…”