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We investigate different postseparation process routes for silicon heterojunction (SHJ) half solar cells, separated by thermal laser separation. SHJ half cells with and without aluminum oxide (Al2O3) deposition as edge passivation layer undergo different annealing processes, including i) a hotplate; ii) an inline oven; and iii) an ultrafast light soaking process. SHJ half cells with an initial efficiency of 21.7% reach 21.9% after Al2O3 deposition and inline oven annealing (pseudo fill factor, pFF, increase of 0.3%abs and series resistance RS decrease by −0.05 Ωcm2). The light soaking process is known to lead to improved surface passivation and carrier transport for SHJ cells. For light soaking processed SHJ half cells, an 21.9% efficiency is obtained (RS reduction by −0.13 Ωcm2 and open-circuit voltage VOC increase by +2 mV compared to the initial half cell). By combining Al2O3 deposition and subsequent light soaking, SHJ half cells reach 22.1% efficiency, resulting from the combined benefits for pFF, RS, and VOC of the two processes. No additional thermal annealing of the Al2O3 layer is necessary, proving that the light soaking process is sufficient to activate the Al2O3 passivation. This allows for a two-step postseparation process sequence, resulting in SHJ half cells featuring similar efficiencies to light soaking processed full cells. SHJ half cells, integrated into one-cell modules after Al2O3 deposition and light soaking, show an efficiency advantage of +0.3%abs in comparison to modules with untreated half cells. Thus, we demonstrate the possibility of compensating separation losses for SHJ half cells and the transferability of the improvements to module level.

This article introduces a postmetallization “passivated edge technology” (PET) treatment for separated silicon solar cells consisting of aluminum oxide deposition with subsequent annealing. We present our work on bifacial shingle solar cells that are based on the passivated emitter and rear cell concept. To separate the shingle devices after metallization and firing, we use either a conventional laser scribing mechanical cleaving (LSMC) process or a thermal laser separation (TLS) process. Both separation processes show similar pseudo fill factor (pFF) drops of - 1.2%abs from the host wafer to the separated state. The pFF of the TLSseparated cells increases by up to +0.7%abs from the as-separated state after PET treatment due to edge passivation, while the pFF of LSMC-separated cells increases by up to +0.3%abs. On cell level, the combination of TLS and PET allows for a designated area output power density of pout = 23.5 mW/cm2, taking into account an additional 10% rear side irradiance.

The authors discuss industry related approaches at Fraunhofer ISE for bifacial p-type silicon solar cells, taking into account the well-known "passivated emitter and rear cell" (PERC), "passivated emitter and rear totally diffused" (PERT) and "passivated emitter and locally diffused" (PERL) architectures. In the case of PERC, challenges in terms of alignment, printability and the importance of bifaciality are addressed. In the case of PERT, a co-diffusion process is utilized to form the emitter and the back surface field simultaneously avoiding also critical shunts that can arise at the edges of such devices. For the PERL technology, the industrial feasible pPassDop approach is discussed. We report on front side energy conversion efficiencies for PERC of 21.4%, PERT of 20.5%, and PERL of 19.8%. Furthermore, bifaciality factors for PERC of 0.7, for PERT of 0.86, and for PERL of 0.89 are presented.