Silicon heterojunction interdigitated back-contact solar cells bonded to glass with efficiency >21%

Abstract

Previously, IMEC proposed the i 2-module concept which allows to process silicon heterojunction interdigitated back-contact (SHJ-IBC) cells on thin (<50 µm) Si wafers at module level. This concept includes the bonding of the thin wafer early on to the module cover glass, which delivers mechanical support to the wafer and thus significantly improves the production yield. In this work, we test silicone and EVA bonding agents and prove them to be resistant to all rear side processes, including wet and plasma processes. Moreover, a lift-off process using a sacrificial SiOx layer has been developed for emitter patterning to replace conventional lithography. The optimized process steps are demonstrated by the fabrication of SHJ-IBC cells on 6-inch 190 µm-thick wafers. Efficiencies up to 22.6% have been achieved on reference freestanding wafers. Excellent Voc of 734 mv and Jsc of 40.8 mA/cm 2 lead to an efficiency of 21.7% on silicone-bonded cells, where the high Voc indicates the process compatibility of the bonding agent. The developments that enabled such achievements and the key factors that limit the device performance are discussed in this paper.

Simulation of an efficient silicon heterostructure solar cell concept featuring molybdenum oxide carrier-selective contact

“…The conversion efficiency of 24.7% was attained for HIT solar cell at the research level by M. Taguchi et al By reducing the recombination losses, Panasonic was able to improve the research cell efficiency to 25.6% . Other cells based on the combination of IBC and HJ have also been recently reported in the literature . Coupled with the higher efficiency and better reliability, SHJ/HIT solar cells are expected to gain a market share of 15% by 2027 that will equally ensure the economic competitiveness of solar energy in the future …”

A novel silicon heterojunction IBC process flow using partial etching of doped a‐Si:H to switch from hole contact to electron contact in situ with efficiencies close to 23%

“…For comparison, reference wafers following the conventional process sequence were also co‐processed in the same run. The details of the different solar cell fabrication processes used in this work have already been described in detail in our previous publications . Here, only the salient features and key differences between the two splits are highlighted.…”

“…Finally, an n + a‐Si:H layer is deposited, again in situ, to form the a‐Si:H (i/n + ) electron contact. All other process steps are identical for the two routes, as depicted in Figure , and explained in detail in another study …”

Laser Assisted Patterning of a-Si:H: Detailed Investigation of Laser Damage

“…Silicon heterojunction interdigitated back‐contact (SHJ‐IBC) solar cells are the subject of many scientific investigations due to their capability to achieve very high energy conversion efficiency; SHJ‐IBC cells combine the advantages of heterojunction technology with a back‐contact scheme . A thin‐hydrogenated amorphous silicon (a‐Si:H) layer is deposited on a crystalline silicon (c‐Si) substrate to significantly reduce the c‐Si surface recombination losses.…”

“…The excellent a‐Si:H/c‐Si passivation quality can lead to a high open‐circuit voltage ( V oc ) value of 750 mV . IBC cells feature both hole and electron collection contacts at the rear side of the device, which eliminates front grid shadowing, leading to a high short‐circuit current density ( J sc ) of 42.3 mA cm −2 . Recently, Kaneka reported the world record efficiency of 26.7% in a SHJ‐IBC cell with an area of 79 cm 2 …”