On the chances and challenges of combining electron‐collecting nPOLO and hole‐collecting Al‐p⁺ contacts in highly efficient p‐type c‐Si solar cells

Abstract

ISFH is following a distinct cell development roadmap, which comprises-as a shortterm concept-the combination of an n-type doped electron-collecting poly-Si on oxide (POLO) junction with an Al-alloyed p + junction for hole collection. This combination can be integrated either in front-and back-contacted back junction cells (POLO-BJ) or in interdigitated back-contacted cells (POLO-IBC). Here, we present recent progress with these two cell concepts. We report on a certified M2-sized 22.9% efficient POLO-BJ cell with a temperature coefficient TC η of only À(0.3 ± 0.02) % rel /K and a certified 23.7% (4 cm 2 d.a.) efficient POLO-IBC cell. We discuss various specific conceptual aspects of this technology and present a simulation-based sensitivity analysis for quantities related to the quality of the hole-collecting alloyed Al-p + junction which are subject to continuous improvement and thus hard to predict exactly. We report that the measured pseudo fill factor values decrease more due to metallization than would be expected from recombination in the metallized regions with an ideality factor of one only. The gap to pseudo fill factor values that are theoretically achievable at the respective open-circuit voltages is 1.1% abs (Ga-doped wafer) for POLO-IBC and 1.4% abs (B-doped wafer) to 2% abs (Ga-doped wafer) for POLO-BJ. With an embedded blocking layer for Ag crystallites in the poly-Si, we present a concept to reduce this gap.

Design of Large Poly‐Si on Oxide Interdigitated Back Contact (POLO IBC) Silicon Solar Cells with Local Al–p+Contacts in the Constraints of Measurement and Module Integration

“…This value is close to 23.7% measured on small cells with DARC. [22] The V oc of our best M2-sized cell with DARC is 711 mV and thus almost the same as the 711.5 mV of our best 4 cm 2 -sized cell. The J sc values are also similar: 41.1 mA cm À2 for M2-sized cells and 41.3 mA cm À2 for 4 cm 2 -sized cells.…”

“…We achieved an energy conversion efficiency of 23.7%, as independently confirmed by ISFH CalTeC. [ 22 ]…”

“…We achieved an energy conversion efficiency of 23.7%, as independently confirmed by ISFH CalTeC. [22] In this work, we report on our progress in upscaling our POLO IBC technology on full M2 wafers with special emphasis on the implications of the busbar layout on the cell performance, the cell interconnection scheme, and cell measurement.…”

“…We showed for the first time M2‐sized POLO IBC cells with an interrupted finger design. We successfully transferred promising I–V parameters previously measured on small area cells [ 10,22 ] in designated area measurements to full area cells. In particular, V oc values up to 718 mV are, to our knowledge, among the highest values reported so far for p‐type cells with alloyed Al–p + regions as hole collecting contacts.…”

Dopant‐free passivating contacts for crystalline silicon solar cells: Progress and prospects

“…Besides, being most compatible with c ‐Si, the SiO 2 interlayer is often used to improve the passivation quality by saturating the dangling bonds and suppressing the element diffusion. In this case, the carriers are believed to pass through the ultra‐thin SiO 2 passivation layer through tunneling and pinholes 188–190 . Attention should be paid to distinguishing SiO 2 passivation layers that are intentionally formed (e.g., by UV/O 3 treatment, chemical and thermal oxide growth, etc.)…”