Interdigitated back contact (IBC) architecture can yield among the highest silicon wafer-based solar cell conversion efficiencies. Since both polarities are realized on the rear side, there is a definite need for a patterning step. Some of the common patterning techniques involve photolithography, inkjet patterning, and laser ablation. This work introduces a novel patterning technique for structuring the rear side of IBC solar cells using the enhanced oxidation characteristics under the locally laser-doped n++ back surface field (BSF) regions with high-phosphorous surface concentrations. Phosphosilicate glass layers deposited via POCl3 diffusion serve as a precursor layer for the formation of local heavily laser-doped n++ BSF regions. The laser-doped n++ BSF regions exhibit a 2.6-fold increase in oxide thickness compared to the nonlaser-doped n+ BSF regions after undergoing high-temperature wet thermal oxidation. The utilization of oxide thickness selectivity under laser-doped and nonlaser-doped regions serves two purposes in the context of the IBC solar cell, first patterning rear side and second acting as a masking layer for the subsequent boron diffusion. Proof-of-concept solar cells are fabricated using this novel patterning technique with a mean conversion efficiency of 20.41%.@en

The high usage of silver in industrial solar cells may limit the growth of the solar industry. One solution is to replace Ag with copper. A screen printable Cu paste is used herein to metallize industrial interdigitated back contact (IBC) solar cells. A novel metallization structure is proposed for making solar cells. Cu paste is applied to replace the majority of the Ag used in IBC cells as busbars and fingers. Cu paste is evaluated for use as fingers, and solar cells are made to test conversion efficiency and reliability. The Cu paste achieves comparably low resistivity, and Cu paste printed cells demonstrate similar efficiency to Ag paste printed cells, with an average efficiency of 23%, and only 4.5 mg W−1 of Ag usage. Also, the solar cells are stable and no Cu in-diffusion is observed under damp heat (85 °C, 85% relative humidity) and thermal stress (200 °C) for 1000 h, respectively. All processes used in this study can be carried out with industrial equipment. These findings reveal a new application for Cu pastes and point to a new direction for reducing Ag utilization and cost.@en

In this study, the edge passivation effectiveness and long-term stability of Nafion polymer in n-type interdigitated back contact (IBC) solar cells are investigated. For new module technologies such as half-cut, triple-cut, or shingled modules, cutting of the cells introduces unpassivated edges with a high recombination rate and this limits the module power. These cut edges can be “repassivated” after cutting and in this work Nafion polymer is used to achieve this. First, different edge types, namely emitter edges (n+/n/p+) and back surface field (BSF) edges (n+/n/n+), as well as different cutting techniques such as laser cut and cleave (L&C), thermal laser separation (TLS), and mechanical cleaving are evaluated. It is found that TLS and mechanical cleaving enable good repassivation on both BSF and emitter edges. Second, industrial-size IBC solar cells are made to assess the effect of the edge repassivation on performance. On 1/4-cut M2 size IBC cells with two emitter edges, efficiency is improved by over 0.3%abs. However, an efficiency improvement was not observed for similar cells with BSF edges, due to an insufficient passivation at the bulk edges. Last, the real-world stability of the Nafion repassivation is evaluated in industrially relevant module stacks by laminating the repassivated wafers with ethylvinylacetate (EVA) or polyolefin elastomer (POE) encapsulants and then exposing them to industry standard testing of 1000 h under damp heat conditions (85 °C, 85% relative humidity). The tests reveal that the repassivation is stable in EVA encapsulants but not in POE.@en

The edge recombination losses of crystalline silicon solar cells become significant when they are cut into smaller pieces to be assembled into modules. With the interdigitated pattern of doped p and n regions on the rear side, the interdigitated back contact (IBC) solar cells can be cut through different doped regions. In this study, the cutting losses in IBC solar cells are investigated and various cutting scenarios are studied. Through simulations and experimental measurements, it is found that the cut losses can be reduced by cutting through the back surface field rather than through the emitter. The losses under low light intensity are reduced to an even greater extent. When a 23% cell is cut into 1/3 pieces, the efficiency can be increased by 1.2%rel (cut related losses were improved from 2.0rel to 0.8%rel under standard 1-sun testing conditions, compared to cutting through the emitter. Under low light intensity of 0.25 sun, the improvement is around 2.4%rel. The improvement is mainly due to lower FF losses in the I-V characteristics, and this is further confirmed by Suns-Voc and PL measurements. In the pFF analysis, the additional losses due to laser damage are also observed. This strategy of cutting through the BSF region in IBC solar cells can be quickly adopted in mass production without the need for additional processes or equipment and both module power and energy yield can be increased.@en

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.@en