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Here, we demonstrate the use of an ultrathin TiO2 film as a passivating carrier-selective contact for silicon photovoltaics. The effective lifetime, surface recombination velocity, and diode quality dependence on TiO2 deposition temperature with and without a thin tunneling oxide interlayer (SiO2 or Al2O3) on p-type crystalline silicon (c-Si) are reported. 5-, 10-, and 20-nm-thick TiO2 films were deposited by thermal atomic layer deposition (ALD) in the temperature range of 80–300 °C using titanium tetrachloride (TiCl4) and water. TiO2 thin-film passivation layers alone result in a lower effective carrier lifetime compared with that with an interlayer. However, SiO2 and Al2O3 interlayers enhance the TiO2 passivation of c-Si surfaces. Further annealing at 200 °C in N2 gas enhances the surface passivation quality of TiO2 tremendously. From these findings, design principles for TiO2–Si heterojunction with optimized photovoltage, interface quality, and electron extraction to maximize the photovoltage of TiO2–Si heterojunction photovoltaic cells are formulated. Diode behaviour was analysed with the help of experimental, analytical, and simulation methods. It is predicted that TiO2 with a high carrier concentration is a preferable candidate for high-performance solar cells. The possible reasons for performance degradation in those devices with and without interlayers are also discussed.

are generated by a repetitive sequence of processing steps in which for each material a sacrificial resist layer is deposited, then patterned, then used to transfer its pattern into the desired material layer, and finally removed. This framework does not allow for the direct deposition of a patterned functional material. Its reliance on a small number of sacrificial "resists" and the multiple removal and cleaning steps cause large amounts of material waste. It also requires significant resources of energy, processing time, and facility investment. Additionally, lithography-based fabrication is highly suitable to the generation of identical products in large numbers, but it does not offer prompt access and flexibility to prototyping individual devices. In the manufacturing of large parts, prototyping has been rendered increasingly accessible using additive manufacturing (3D printing) strategies. [4][5][6][7][8] Here, the functional material is directly deposited in patterned form using various strategies such as miniaturized nozzles and laser or electron beams. However, so far the resolution (the smallest feature size controllable) has been on the order of hundreds of micrometers, although the integration of nanostructures into 3D-printed materials or patterns is possible. [9][10][11][12][13][14][15][16][17][18] In other words, 3D printing is several orders of magnitude away from the feature sizes accessible by lithographic methods. In summary, 3D printing has the direct pattern generation capability and materials versatility, whereas Additive manufacturing (3D printing) has not been applicable to micro-and nanoscale engineering due to the limited resolution. Atomic layer deposition (ALD) is a technique for coating large areas with atomic thickness resolution based on tailored surface chemical reactions. Thus, combining the principles of additive manufacturing with ALD could open up a completely new field of manufacturing. Indeed, it is shown that a spatially localized delivery of ALD precursors can generate materials patterns. In this "atomic-layer additive manufacturing" (ALAM), the vertical resolution of the solid structure deposited is about 0.1 nm, whereas the lateral resolution is defined by the microfluidic gas delivery. The ALAM principle is demonstrated by generating lines and patterns of pure, crystalline TiO 2 and Pt on planar substrates and conformal coatings of 3D nanostructures. The functional quality of ALAM patterns is exemplified with temperature sensors, which achieve a performance similar to the industry standard. This general method of multimaterial direct patterning is much simpler than standard multistep lithographic microfabrication. It offers process flexibility, saves processing time, investment, materials, waste, and energy. It is envisioned that together with etching, doping, and cleaning performed in a similar local manner, ALAM will create the "atomic-layer advanced manufacturing" family of techniques.The ORCID identification number(s) for the author(s) of this article can be found und...

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