Design and optimization of hole collectors based on nc-SiOx:H for high-efficiency silicon heterojunction solar cells

Low activation energy (E-a) and wide bandgap (Eg) are essential for (p)-contacts to achieve effective hole collection in silicon heterojunction (SHJ) solar cells. In this work, we study Plasma-Enhanced Chemical Vapor Deposition p-type hydrogenated nanocrystalline silicon oxide, (p)nc-SiOx:H, combined with (p)nc-Si:H as (p)-contact in front/back-contacted SHJ solar cells. We firstly determine the effect of a plasma treatment at the (i)aSi:H/(p)-contact interface on the thickness-dependent E-a of (p)-contacts. Notably, when the (p)nc-Si:H layer is thinner than 20 nm, the E-a decreases by applying a hydrogen plasma treatment and a very-high-frequency (i)ncSi:H treatment. Such an interface treatment also significantly reduces the contact resistivity of the (p)-contact stacks (rho(c,p)), resulting in an improvement of 6.1%abs in fill factor (FF) of the completed cells. Thinning down the (i)a-Si:H passivating layer to 5 nm leads to a low rho(c,p) (144 m Omega.cm(2)) for (p)-contact stacks. Interestingly, we observe an increment of FF from 72.9% to 78.3% by using (p)nc-SiOx:H layers featuring larger differences between their optical gap (E-04) and E-a, which tend to enhance the built-in potential at the c-Si/(i)a-Si:H interface. Furthermore, we observe clear impacts on rho(c,p), open-circuit voltage, and FF by optimizing the thicknesses of (p)-contact that influence its E-a. In front junction cells, the vertical and lateral collection of holes is affected by rho(c,p) of (p)-contact stacks. This observation is also supported by TCAD simulations which reveal different components of lateral contributions. Lastly, we obtain both front and rear junction cells with certified FF well-above 80% and the best efficiency of 22.47%.

Automated summary

This study focuses on optimizing (p)-contacts in silicon heterojunction solar cells, showing that plasma treatment and thickness play significant roles in improving contact resistivity and fill factor. Optimal interface treatment and thickness can enhance hole collection efficiency and overall cell performance.