Industrial implementation of 24%-efficient POLO IBC solar cells and future upgrade to 26%-efficient POLO 2 IBC

abstract

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 SiOxNy/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 AlOx/SiN tools good surface passivation is demonstrated by obtaining an iVoc up to 727mV using textured, rear side polished AlOx/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 SiOx/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 SiOx and the in-situ doped p-type polysilicon layer. ISFH is applying the SiOx/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 Voc=735mV of POLO2 IBC cells processed without metal contacts. Since the polysilicon contacts minimize carrier recombination at metal contacts, the implied Voc value demonstrates the high Voc potential of this promising new POLO2 IBC manufacturing process thereby indicating a conversion efficiency potential above 26%.