Laser Patterning of Thin Films

Abstract

Laser‐based patterning of thin films has rapidly revolutionized materials processing over the last years and is increasingly replacing conventional patterning techniques such as photolithography or mechanical patterning. Currently, it is widely used for both fundamental research and practical applications. According to the desired requirements, laser and processing parameters can be specifically selected for selective, precise, reproducible, and nearly damage‐free patterning of single layers and layer stacks of a wide variety of materials. This article summarizes the fundamentals and basic processes of laser ablation and discusses the influence of the essential laser parameters on laser–matter interaction. Moreover, an overview on practical aspects such as different optical setups, process control and approaches for selective layer ablation are given. A variety of current examples for the application of lasers for patterning thin films is introduced with a clear focus on photovoltaic applications. These examples highlight that laser patterning is a versatile, flexible, and reliable technique for processing a wide range of thin‐film materials, which will be increasingly implemented in the future.

Can Nanosecond Laser Achieve High‐Performance Perovskite Solar Modules with Aperture Area Efficiency Over 21%?

“…Compared with patterning from the film side (defined as direct ablation), the induced ablation provides a series of advantages including sharp‐edged patterns, smaller HAZs, and avoidance of screening by the plume. [ 6 ] The laser processing consists of three sequential scribing steps, that is, P1, P2, and P3 (Figure 1c). P1 aims to separate the ITO film into strips to define the individual sub‐cells deposited over the scribed ITO film.…”

“…The Gaussian distribution of the laser power leads to locations in the beam where the energy is below the ablation threshold of vaporization of the materials, resulting in a material that is not removed but just being heated. The TPD can be estimated as follows: [ 6 ] $$\[{L_{th}} = 2\sqrt {{D_{\rm{t}}} \times {\tau _{\rm{p}}}} = 2\sqrt {\frac{{{\rm{k}}{\tau _{\rm{p}}}}}{{\rho {\rm{c}}}}} \]$$where D t is the thermal diffusion coefficient, τ p is the pulse duration, k is the thermal conductivity, ρ is the density, and c is the specific heat capacity. According to literature reports, the D t at room temperature of perovskite material is generally nearly two orders of magnitude smaller than that of other established thin film materials.…”

“…[5] The laser photons are absorbed by the solar cell materials and their energy is first absorbed by free electrons, and then transferred to the lattice, leading to material gasification. [6] Thus, the longer the pulse duration, that is, the more the laser pulse exceeds the duration of the electron-lattice interaction, the more likely it is to generate a larger heat-affected zone (HAZ), as excess energy diffuses into the material in the form of lattice vibrations. Therefore, lasers generating ultrashort (picosecond or femtosecond) pulses are more attractive for processing devices that are sensitive to the presence of a HAZ rather than the short pulse laser (nanosecond).…”

Improved Electrical Performance of Perovskite Photovoltaic Mini‐Modules through Controlled PbI2 Formation Using Nanosecond Laser Pulses for P3 Patterning

“…The general principles of laser patterning of thin films are described in our earlier work. [6] These principles and approaches have been widely applied to the full laser patterning of PSMs, [7][8][9][10] with most attention given to the P2 step for patterning of the perovskite absorber layers. Nevertheless, several challenges regarding the P3…”

“…Longer pulse durations deposit more thermal energy into the target material, which can propagate away from the original target area through the material lattice. [6,7] These ns/ps P3 lines were scribed on 3-cell PSMs with an active area of 2.2 cm 2 per module. The parameters for P1 and P2 patterning are the same for all samples (see Section 2.2).…”