Towards 25 % interdigitated back-contact solar cells on Ga-doped Cz-Si using a lean industrial process flow

article
2026
authors
Larionova, Yevgeniya and Köhler, Adrian and Hussein, Karima and Helmich, Lailah and Schimanke, Sabrina and Ripke, Melanie and Veurman, Welmoed and Jäger, Philip and Baumann, Ulrike and Brendel, Rolf and Dullweber, Thorsten
journal
Solar Energy Materials and Solar Cells
doi:10.1016/j.solmat.2026.114540

abstract

In this work, we present recent advancements in the development of high-efficiency POLO IBC (poly-Si on oxide interdigitated back contact) solar cells fabricated on M2-sized wafers using industrial processing equipment. As the PV industry is currently in transition from PERC and transitioning beyond TOPCon towards next-generation IBC architectures, our IBC concept offers a lean and production-compatible process flow that largely reuses existing PERC manufacturing tools. Efficiency improvements to 24.5 %, independently confirmed by ISFH CalTeC, were achieved through two key optimizations: (1) enhancement of the front-side antireflection coating using an additional PECVD SiOvNz layer in an AlOx/SiNy/SiOvNz stack, reducing optical reflection by up to 0.7 %abs and improving Jsc by approximately 0.4 mA/cm2; and (2) the metallization process was optimized by changing the Ag paste, reversing the Al and Ag printing sequence and reducing the Ag finger opening width. To identify the main loss mechanisms and quantify the efficiency potential, we simulate the 24.5 %-efficient POLO IBC cell using Quokka3 with experimentally derived input parameters and apply a Synergistic Efficiency Gain Analysis (SEGA). The SEGA reveals that the dominant losses in the present cell are: (i) insufficient front-side surface passivation, (ii) high recombination under the screen-printed Ag contacts on n-type poly-Si, and (iii) elevated recombination and contact resistivity at the laser contact opening of the Al-BSF hole contact. In the optimized scenario we simulate a realistically achievable efficiency of 25.54 %, demonstrating that efficiencies beyond 25 % are within reach for this lean POLO IBC architecture.