Hydrogen plays a critical role in the manufacturing of photovoltaic (PV) cells, particularly in enhancing efficiency, stability, and performance. Its applications span multiple stages of PV production, including passivation of silicon solar cells, thin-film deposition, and defect engineering. The influence of hydrogen varies between crystalline silicon and thin-film technologies, each leveraging its unique properties to address material-specific challenges.

In crystalline silicon solar cells, hydrogen is primarily used for passivation, a process that mitigates defects and improves carrier lifetimes. Silicon wafers inherently contain impurities and structural defects that act as recombination centers for charge carriers, reducing cell efficiency. Hydrogen atoms, when introduced during or after cell fabrication, bond with dangling silicon bonds and other defects, neutralizing their detrimental effects. This is commonly achieved through hydrogenation, where hydrogen is diffused into the silicon lattice either from hydrogen-rich dielectric layers like silicon nitride or via post-deposition annealing in a hydrogen-containing atmosphere. The effectiveness of hydrogen passivation depends on the temperature, duration of treatment, and the source of hydrogen. For example, silicon nitride layers deposited by plasma-enhanced chemical vapor deposition (PECVD) release hydrogen during annealing, which then permeates the silicon bulk.

Thin-film solar cells, such as those based on amorphous silicon (a-Si), cadmium telluride (CdTe), or copper indium gallium selenide (CIGS), also rely on hydrogen but in different ways. In a-Si solar cells, hydrogen is integral to the material itself, as it passivates dangling bonds in the amorphous network. Without hydrogen, a-Si would have an unacceptably high defect density, making it unsuitable for PV applications. The hydrogen content in a-Si films typically ranges between 5 to 15 atomic percent, balancing defect passivation with material stability. Excessive hydrogen can lead to light-induced degradation, known as the Staebler-Wronski effect, where prolonged exposure to sunlight increases defect density and reduces efficiency.

In CdTe and CIGS thin-film technologies, hydrogen is used for defect passivation and doping control. For CdTe, hydrogen can passivate grain boundaries and deep-level defects, improving minority carrier lifetimes. Hydrogen incorporation is often achieved during deposition or through post-deposition treatments in hydrogen plasma. Similarly, in CIGS cells, hydrogen helps neutralize selenium vacancies and other defects that act as recombination centers. The interaction of hydrogen with these complex multinary compounds is less straightforward than in silicon, requiring precise control to avoid unintended doping effects or phase segregation.

Defect engineering is another critical application of hydrogen in PV manufacturing. In both crystalline and thin-film technologies, hydrogen can be used to tailor the electronic properties of materials. For instance, in silicon heterojunction (SHJ) solar cells, hydrogen passivation at the interface between amorphous and crystalline silicon layers reduces interface recombination, enabling higher open-circuit voltages. In perovskite solar cells, an emerging technology, hydrogen has been explored for stabilizing the perovskite lattice and passivating ionic defects, though its role is still under investigation compared to traditional PV materials.

The differences in hydrogen’s role between crystalline silicon and thin-film technologies stem from their distinct material properties and defect structures. Crystalline silicon benefits from hydrogen’s ability to diffuse deeply into the bulk, passivating defects uniformly. In contrast, thin-film materials often require hydrogen to be incorporated during deposition due to their limited diffusion lengths and higher defect densities at grain boundaries. Additionally, the thermal budgets for hydrogen treatments vary significantly—crystalline silicon can withstand high-temperature annealing, while thin-film materials often require low-temperature processes to avoid degradation.

Hydrogen also contributes to the stability and longevity of PV modules. In crystalline silicon modules, hydrogen can migrate over time under operational stresses, such as thermal cycling or UV exposure, leading to changes in passivation effectiveness. Understanding these dynamics is crucial for predicting module degradation and improving durability. Thin-film modules face similar challenges, where hydrogen redistribution can influence defect densities and performance over time.

Despite its benefits, the use of hydrogen in PV manufacturing presents challenges. Precise control over hydrogen concentration and distribution is necessary to avoid detrimental effects, such as blistering in silicon or increased defect densities in thin films. Process optimization is essential to ensure consistent performance across production batches. Furthermore, the source of hydrogen—whether from process gases, dielectric layers, or post-treatment plasmas—must be carefully selected to match the requirements of the specific PV technology.

In summary, hydrogen is indispensable in photovoltaic manufacturing, serving as a versatile tool for defect passivation, thin-film deposition, and performance enhancement. Its applications differ between crystalline silicon and thin-film technologies, reflecting the unique material challenges each faces. As PV technologies continue to evolve, optimizing hydrogen’s role will remain a key factor in achieving higher efficiencies and more reliable solar cells. Future advancements may explore novel hydrogenation techniques or alternative passivation methods to further push the boundaries of PV performance.