Role of polysilicon in poly-Si/SiO x passivating contacts for high-efficiency silicon solar cells

Lee

Progress in Photovoltaics

et al. 2019

Self Cite

This study proposes a hybrid solar cell structure for a highly efficient silicon solar cell obtained by combining two passivating contact structures, namely, a heterojunction and polysilicon passivating contact. Given that the major cause of the loss in efficiency of crystalline silicon solar cells is carrier recombination at the metal‐semiconductor junction, a passivating contact having high‐quality passivation and a low contact resistance was introduced. In this study, two major passivating contact solar cells were combined. By applying an intrinsic thin amorphous silicon layer at the front and a tunneling oxide at the rear, a hybrid silicon solar cell with an efficiency of 21.8% was fabricated. Moreover, to evaluate the potential efficiency limit and to suggest methods for improving the cell performance of the proposed amorphous silicon emitter tunnel oxide back contact structure, the cell efficiency was simulated, and the result indicated that an efficiency of 26% could be achieved by controlling the thickness and resistivity of the wafer.

Section: Resultsmentioning

confidence: 89%

Section: Methodsmentioning

confidence: 99%

Tunnel oxide passivating electron contacts for high‐efficiency n‐type silicon solar cells with amorphous silicon passivating hole contacts

Lee

Progress in Photovoltaics

et al. 2019

Self Cite

ACS Appl. Mater. Interfaces

“…To further improve the chemical passivation of SiO x , hydrogenation treatment is commonly applied. The passivation quality of poly-Si/SiO x structures is sensitive to the hydrogen content around the SiO x interfacial layer. , The crystalline silicon (c-Si)/SiO x interface state density ( D it ) has been shown to be reduced by injecting hydrogen, , which can be achieved via forming gas anneal (FGA) , or by coating with a hydrogen-rich layer, such as silicon nitride (SiN x ) − or aluminum oxide (AlO x ), , followed by thermal annealing.…”

Section: Introductionmentioning

confidence: 99%

Optimum Hydrogen Injection in Phosphorus-Doped Polysilicon Passivating Contacts

Kang

Sio

Stückelberger

et al. 2021

It has previously been shown that ex situ phosphorus-doped polycrystalline silicon on silicon oxide (poly-Si/SiO x ) passivating contacts can suffer a pronounced surface passivation degradation when subjected to a firing treatment at 800 °C or above. The degradation behavior depends strongly on the processing conditions, such as the dielectric coating layers and the firing temperature. The current work further studies the firing stability of poly-Si contacts and proposes a mechanism for the observed behavior based on the role of hydrogen. Secondary ion mass spectrometry is applied to measure the hydrogen concentration in the poly-Si/SiO x structures after firing at different temperatures and after removing hydrogen by an anneal in nitrogen. While it is known that a certain amount of hydrogen around the interfacial SiO x can be beneficial for passivation, surprisingly, we found that the excess amount of hydrogen can deteriorate the poly-Si passivation and increase the recombination current density parameter J 0. The presence of excess hydrogen is evident in selected poly-Si samples fired with silicon nitride (SiN x ), where the injection of additional hydrogen to the SiO x interlayer leads to further degradation in the J 0, while removing hydrogen fully recovers the surface passivation. In addition, the proposed model explains the dependence of firing stability on the crystallite properties and the doping profile, which determine the effective diffusivity of hydrogen upon firing and hence the amount of hydrogen around the interfacial SiO x after firing.

“…The higher doping causes a reduced interfacial recombination as the minority carriers’ concentration is smaller. [ 31,32 ] This reduces the surface recombination velocity and thus passivation quality is higher for Group—POCl 3 than for Group—Im15.…”

Section: Resultsmentioning

confidence: 99%

Sputtered Phosphorus‐Doped poly‐Si on Oxide Contacts for Screen‐Printed Si Solar Cells

et al. 2022

The impact of the phosphorus doping density in direct current‐sputtered polysilicon layers on surface passivation and contact resistance by fabricating polysilicon on oxide (POLO) contacts is studied, when applying doping densities ranging from 3 × 1019 to 4 × 1020 cm−3. Hydrogenation is performed either via a hydrogen‐releasing AlO x layer and postdeposition anneals in forming gas using a tube furnace at 400 °C, or by rapid firing of an AlO x /SiN y stack in a conveyor belt furnace at 810 °C. The study shows that the forming gas anneal of the weakly in situ phosphorus‐doped poly‐Si layers with AlO x enables a passivation quality with an implied open‐circuit voltage of up to 734 mV and a recombination current density down to 1.8 fA cm− 2. For fast firing, a high phosphorus concentration of 4 × 1020 cm−3 is required for comparably high passivation quality with a recombination current density down to 1.3 fA cm− 2. A p‐type POLO back‐junction solar cell featuring such ex situ doped sputtered POLO contacts with a cell efficiency of 22.4% and an open‐circuit voltage of 714 mV is fabricated. To our knowledge, this is the highest open‐circuit voltage published so far with sputtered POLO contacts.