Industrial implementation of 24%-efficient POLO IBC solar cells and future upgrade to 26%-efficient POLO²IBC

IBC solar cells have gained tremendous interest in the PV industry as next-generation technology. ISFH has developed a lean manufacturing process sequence for POLO IBC solar cells applying p-type Cz wafers, an Al-BSF base contact and local PECVD deposition of the SiO_xN_y/n-type polysilicon emitter through a glass shadow mask. In this paper, we report a new best POLO IBC cell efficiency of 24.5% processed at ISFH on M2 wafer size. In 2024, we started to transfer the POLO IBC process from the ISFH SolarTeC to the Kalyon PV manufacturing line using their M10 sized p-type Ga-doped Cz wafers and cell production tools. With Kalyon PV's wet chemistry and PECVD AlO_x/SiN tools good surface passivation is demonstrated by obtaining an iV_oc up to 727mV using textured, rear side polished AlO_x/SiN passivated test wafers. Kalyon PV targets to process first M10-sized POLO IBC solar cells till end of 2025. However, the POLO IBC efficiency will be limited to below 25.5% by the carrier recombination at the Al-BSF base contact. To overcome this limitation aiming at n-type poly / p-type polysilicon POLO² IBC cell efficiencies beyond 26%, EnPV and ISFH optimized a carrier selective SiO_x/p-type polysilicon layer stack yielding a new best median saturation current density J₀ =4±1 fA/cm² using industrial tools for the wet chemically grown SiO_x and the in-situ doped p-type polysilicon layer. ISFH is applying the SiO_x/p-type polysilicon layer stack to develop a novel industrial processing sequence for the POLO² IBC solar cell. We deposit both polysilicon layers in-situ-doped full-area and laser-structure both polysilicon polarities. Using lab-type tools and p-type float zone (FZ) wafers, a small-area POLO² IBC solar cell with 25.5% efficiency has been developed at ISFH. Using M2-sized n-type Cz wafers, a novel IBC trench patterning process, and solely industrial processing tools in the ISFH SolarTeC targeting very cost-effective processes for etch barrier formation, laser structuring, and polysilicon etching, we obtain a measured implied V_oc =735mV of POLO² IBC cells processed without metal contacts. Since the polysilicon contacts minimize carrier recombination at metal contacts, the implied V_oc value demonstrates the high V_oc potential of this promising new POLO² IBC manufacturing process thereby indicating a conversion efficiency potential above 26%.