Liquid-phase crystallized silicon absorber layers have been applied in heterojunction solar cells on glass substrates with 10.8% conversion efficiency and an open-circuit voltage of 600 mV. Intermediate layers of SiO x , SiN x , and SiO x N y , as well as the a-Si:H precursor layer, were deposited on 30 cm × 30 cm glass substrates using industrial-type plasma-enhanced chemical vapor deposition equipment. After crystallization on 3 cm × 5 cm area using a continuous-wave infrared laser line, the resulting polysilicon material showed high material quality with large grain sizes. Index Terms-Heterojunction, liquid-phase crystallization, plasma-enhanced chemical vapor deposition (PECVD), thin-film silicon.

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This work reports a laser firing technique applied to completed silicon heterojunction interdigitated back contact solar cells in order to lower contact resistance. Previously, the implementation of a-Si:H(i) at the electron contact of polycrystalline silicon solar cells on glass substrates led to an increase in series resistance. The cell architecture with the current record efficiency of 14.2 % (with illumination through glass) utilizes only an a-Si:H(n+) layer and 2 −2.9 mA cm −2 of short circuit current density is lost due to electrical shading under the electron contact [1],[2]. The goal of implementing an a-Si:H(i) layer and laser firing at this contact is to achieve low contact resistance at fired spots while preserving a-Si:H(i) passivation in unfired regions. After the laser firing, V OC was retained, while up to 14 % absolute increase in FF was obtained with a mere 0.2 mA cm −2 loss in J SC. In the best performing cell, a 72.1 % FF was achieved with a 0.7 mA cm −2 loss in J SC. Two laser sources were used to first ablate a part of the silver contact metal, and then to laser fire through the Si(n)/a-Si:H(i/n+)/ITO/Ag contact. The optimal laser fluence was found to be 1.1 −0.5 J cm −2 (355 nm, picosecond pulse duration) and 4.4 −5.2 J cm −2 (532 nm, nanosecond pulse duration), respectively. The upper limit on specific contact resistance in the laser fired spots was calculated to be 38 ± 20 mΩ cm 2 as a conservative estimate.

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