Industrially viable diffused IBC solar cells using APCVD dopant glass layers

Abstract

Even though interdigitated back contact (IBC) architecture produces the most efficient solar cells, it is difficult to make them cost-effective and industrially viable. Therefore, single-sided atmospheric pressure chemical vapor deposition (APCVD) is investigated for the fabrication of IBC solar cells because it reduces the overall thermal budget, simplifies wet bench processing, and requires no additional masking layer. For the fabrication of a full APCVD IBC solar cell, a very lightly doped front surface field (FSF) of 650 Ω/sq, a heavier doped back surface field (BSF) of 100 Ω/sq and a moderately doped emitter of 250 Ω/sq was used. The high-temperature annealing step is partially done in an oxygen (O2) environment to (i) drive in dopants, (ii) prevent the formation of a boron-rich layer in case of p+ doped c-Si, and (iii) grow an in-situ SiO2 at the Si/dopant glass interface. The etch rate difference between the in-situ grown SiO2 and the doped glass layer is utilized to etch the doped glass completely. The retained in-situ SiO2 after etching is capped with plasma-enhanced chemical vapor deposited (PECVD) SiNx for the passivation of both polarities of IBC solar cells. A full APCVD IBC solar cell precursors (i.e. before metallization) obtained implied open-circuit voltage (iVoc) of 714 mV and emitter saturation current density (J0s) of 17 fA/cm2. At the device level, a full APCVD IBC solar cell achieved a conversion efficiency of 22.8% with Voc of 696 mV and short-circuit current density JSC of 41.3 mA/cm2. These parameters are comparable to the commercially available full-tube diffused ZEBRA® IBC solar cells.