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%.

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) SiN_x 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 (iV_oc) of 714 mV and emitter saturation current density (J_0s) of 17 fA/cm². At the device level, a full APCVD IBC solar cell achieved a conversion efficiency of 22.8% with V_oc of 696 mV and short-circuit current density J_SC of 41.3 mA/cm². These parameters are comparable to the commercially available full-tube diffused ZEBRA® IBC solar cells.

In this work, we developed an in situ annealing process to crystallize boron-doped amorphous silicon [a-Si(p+)] layers deposited by atmospheric pressure chemical vapour deposition (APCVD) to form boron-doped polycrystalline silicon [poly-Si(p+)] layers. The influence of the temperature profiles during a-Si(p+) inline deposition on structural, electrical, and passivation properties was studied in detail. The results show that a-Si(p+) layers can be successfully crystallized by fine-tuning the temperature profiles in the postdeposition zones of the APCVD tool. It was observed that the hydrogenation processes during the fast firing play a significant role in enhancing the passivation quality as well as the electrical properties of the in situ annealed poly-Si(p+) layers. The sheet resistance (Rsh) and implied open circuit voltage (iVoc) of the best in situ annealed poly-Si(p+) layers were found to be comparable to the ones that were ex situ annealed in the tube furnace at 950 $^{\circ }$C for 30 min. The sheet resistance of 200 $\Omega$/$\square$ could be obtained on 150-nm thick poly-Si(p+) layers with an (iVoc) of 718 mV. The use of this novel in situ annealing process to form poly-Si(p+) layers opens a new horizon for a lean process sequence without the additional high-temperature annealing step for fabricating solar cells concepts based on passivating contact.

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.

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.