In a remarkable advancement poised to reshape the landscape of solar technology, researchers have unveiled a pioneering method employing close-space sublimation (CSS) to deposit perovskite layers for tandem solar cells directly on silicon substrates. This novel approach brings forth a synergy of precision, efficiency, and scalability that could pave the way for next-generation, high-performance photovoltaic devices, combining the benefits of perovskite materials with the mature silicon solar cell technology. The technique’s capacity to produce uniform, high-quality perovskite films over large areas under controlled conditions marks a significant leap in tandem solar cell fabrication.
At the core of this innovative method lies the meticulous preparation of pre-patterned indium tin oxide (ITO)-coated glass substrates, which undergo rigorous cleaning treatments to ensure pristine surfaces. These substrates serve as the foundation upon which multidimensional deposition processes unfold. The use of a vacuum chamber integrated within a nitrogen-filled environment allows for the delicate sublimation of organic and inorganic precursors, thereby preventing unwanted degradation and contamination. Such a controlled atmosphere is essential for maintaining the intrinsic properties of the perovskite layers and the interfaces crucial for efficient charge extraction.
The detailed sublimation parameters are finely tuned: the organic charge transport materials, such as TaTm and C60, are deposited at rates ensuring thin, consistent layers that facilitate charge movement and reduce recombination losses. The P-doped hole transport layer, formed by co-sublimating the organic semiconductor TaTm with the dopant CS90112, is carefully controlled to balance conductivity and stability. Concurrently, the team applies an inorganic scaffold through CSS, composed of lead halide mixtures including PbI2 and PbBr2 in varying molar ratios. These scaffolds achieve thicknesses around 250 nm, crucial for optimal light absorption and carrier collection.
One of the distinctive features of this research is the custom-designed powder bed for organic precursors composed of methylammonium iodide (MAI) and methylammonium bromide (MABr). By mechanically blending these salts into homogeneous mixtures and conducting rigorous two-stage thermal tempering, the researchers ensure reproducible and stable source conditions. This methodical preparation guarantees that sublimation rates remain consistent across experimental rounds, thereby enhancing the reliability of the film growth and device results.
Recognizing the sensitivity of perovskite layers to environment and processing conditions, an elaborate pre-deposition conditioning protocol was instituted. This involved stabilizing the source and substrate plates through repeated heating cycles under low-pressure conditions, finely tuning the evaporation equilibrium before actual film deposition. Additionally, post-deposition thermal annealing is conducted in a controlled humidity atmosphere, further enhancing crystallinity and passivation of the perovskite films, which are critical for high photovoltaic performance and stability.
The team takes meticulous care in evaluating the effects of surface treatments such as dynamic washing with isopropanol. Interestingly, in their comprehensive analysis, they found that omitting the washing step does not adversely affect device efficiency, highlighting the robustness of the CSS process and the as-deposited film morphology. For defect passivation, an ethylene-diammonium di-iodide (EDAI2) layer is evaporated under high vacuum, enhancing interfacial quality and reducing nonradiative recombination pathways that inevitably handicap device performance.
Fabrication advances also extend to the tandem solar cells themselves. Silicon bottom cells, cleaned and prepared with precise sonicating and UV-ozone treatments, receive additional hole transport layers sputtered from nickel oxide targets. In particular, for textured silicon substrates, which offer increased light trapping, the deposition thicknesses are scaled up appropriately to ensure conformal coverage, a key factor in preserving device uniformity and efficiency. The replacement of bathocuproine (BCP) with atomic layer deposited (ALD) SnO2 as the buffer layer signifies innovation aimed at protecting underlying layers during transparent conductive oxide (TCO) deposition.
The ALD process highlighted involves an intricate balance between temperature settings and precursor pulsing, utilizing tetrakis(dimethylamino)tin (TDMASn) and water vapor for layer growth. The precise timing and sequence of precursor exposure and purging ensure the formation of uniform, pinhole-free SnO2 films critical for electrode protection and charge management. Additionally, sputtered indium zinc oxide (IZO) layers serve as transparent electrodes atop the devices, contributing both to electrical conductivity and optical transparency required for high overall device efficiency.
Characterization techniques reflect the rigor applied throughout the research. Current-voltage (J-V) measurements under standardized illumination conditions provide essential performance metrics, with careful consideration of scan rates, delay times, and mask-defined active areas to precisely quantify photovoltaic parameters. Tandem devices specifically employ class AAA LED-based solar simulators calibrated with certified reference cells, capturing the nuanced behavior of stacked devices under realistic operational conditions.
Complementing electrical evaluation, spectral response methods such as external quantum efficiency (EQE) elucidate wavelength-resolved photoresponse, with tailored optical biasing of sub-cells allowing for selective interrogation of perovskite and silicon layers. This level of spectral dissection affords insights into current matching and voltage losses, vital for optimizing tandem cell architectures. Suns-Voc measurements further dissect open-circuit voltage contributions from individual sub-cells, applying selective illumination to unravel recombination mechanisms and interface quality.
The research team deploys an arsenal of structural characterization tools to interrogate film quality and crystallinity. X-ray diffraction (XRD) and grazing incidence techniques, alongside grazing-incidence wide-angle X-ray scattering (GIWAXS), reveal crystallographic orientations, phase purity, and grain coherence, which are directly linked to optoelectronic properties. SEM imaging provides nanoscale morphological insights, while photoluminescence mapping and photocarrier grating measurements elucidate carrier dynamics, non-radiative recombination, and uniformity—factors crucial to predictive device modeling and scalability.
This comprehensive approach exemplifies how precise material synthesis, interface engineering, and rigorous characterization converge to push the frontier of perovskite/silicon tandem solar cells. By harnessing close-space sublimation, a technique known for its scalability and industrial compatibility, this research opens avenues for mass production of tandem photovoltaics with efficiencies that could surpass the limits of single-junction devices while remaining cost-effective.
Moreover, the integration of these devices on textured silicon substrates enhances light management and increases photogenerated current while maintaining compatibility with existing silicon manufacturing practices. This symbiotic relationship between novel perovskite materials and well-established silicon technology hints at a compelling future where high-performance, low-cost solar modules become accessible on a commercial scale.
The meticulous attention to source material preparation, deposition parameters, and post-processing ensures reproducibility—a critical attribute for transitioning from laboratory prototypes to industrial applications. The robustness of the CSS technique in tailoring material composition gradients and film thickness also promises customizability, enabling the fine-tuning of bandgaps necessary for optimized multi-junction cell architectures.
In conclusion, this breakthrough showcases close-space sublimation as not merely a fabrication step but a versatile platform enabling the assembly of complex perovskite/silicon tandem solar cells with reproducible, high-quality interfaces and outstanding photovoltaic performance. As the quest for sustainable and scalable solar energy solutions intensifies, such innovations are paramount in meeting global energy demands while reducing environmental footprint.
Subject of Research: Perovskite/silicon tandem solar cells fabricated via close-space sublimation deposition techniques.
Article Title: Close-space sublimation as a versatile deposition process for efficient perovskite silicon tandem solar cells.
Article References:
Diercks, A., Chozas-Barrientos, S., Gil-Escrig, L. et al. Close-space sublimation as a versatile deposition process for efficient perovskite silicon tandem solar cells. Nat Energy (2026). https://doi.org/10.1038/s41560-026-02068-9
DOI: https://doi.org/10.1038/s41560-026-02068-9
