Front-Electrode Engineering Pushes Perovskite/Silicon Tandem Solar Cells to 33% Efficiency

Perovskite/silicon tandem solar cells have long been heralded as the technology that will carry photovoltaics beyond the limits of silicon, and a new study now shows that one of the most overlooked components of these devices—the front electrode—may hold the key to unlocking their full potential. Researchers report monolithic perovskite/silicon tandem cells reaching a power conversion efficiency of 33.06%, with a certified value of 32.28%, achieved not through exotic new absorber chemistry but through the careful co-optimization of the transparent conductive oxide and the metal grid that sits atop the cell. The work, published in Advanced Science, offers a practical blueprint for the industrialization of tandem technology at a moment when global photovoltaic capacity has surged to nearly 3 terawatts and solar power now supplies more than 10% of global electricity demand.

The motivation behind the study stems from a fundamental tension in solar cell design. Crystalline silicon cells, the workhorse of the photovoltaic industry, have reached a record efficiency of 28.1%, uncomfortably close to their theoretical ceiling of 29.4%. Perovskite/silicon tandems sidestep this bottleneck by stacking a wide-bandgap perovskite absorber on top of a silicon bottom cell, allowing the device to harvest different portions of the solar spectrum. Yet while the past decade has seen intense research into perovskite passivation, interconnecting layers, and sub-cell compatibility, the front electrode—the transparent conductive oxide layer paired with an opaque metal grid—has received comparatively little attention. In most tandem configurations, the transparent conductive oxide extracts charge carriers from the transport layer and moves them laterally to the metal grid, which then feeds the current into the external circuit. Every step of that journey dissipates energy, and the metal grid itself casts shadows that block incoming light.

The research team began by replacing the industry-standard transparent electrode material, zinc-doped indium oxide (IZO), with tungsten-doped indium oxide (IWO). Both films, roughly 40 nanometers thick, were deposited on quartz glass by reactive plasma deposition. Optical measurements showed that IWO maintained an average transmittance of 80.5%, slightly better than IZO’s 80.0%, with the advantage concentrated at wavelengths above 450 nanometers—particularly in the near-infrared region that matters enormously for tandem cells, where the silicon bottom cell depends on long-wavelength photons passing through the front layers. Hall effect measurements revealed that IWO also carried a higher carrier concentration of 3.88 × 10²⁰ cm⁻³ compared with IZO’s 3.55 × 10²⁰ cm⁻³, along with improved mobility, cutting the sheet resistance from 99.0 to 88.5 ohms per square and thereby reducing lateral resistive losses.

The electrical benefits of IWO extended deep into the device physics. Kelvin probe force microscopy and ultraviolet photoelectron spectroscopy showed that IWO possesses a work function of just 4.87 electron-volts, substantially lower than the 5.46 eV of IZO and the 5.54 eV of the tin oxide buffer layer beneath it. This favorable energy-level alignment narrows the energetic offset between the electrode and the adjacent functional layers, facilitating efficient electron extraction. Photoluminescence measurements confirmed the consequence: perovskite stacks paired with IWO exhibited weaker emission and shorter carrier lifetimes, signatures of faster carrier removal rather than recombination. Luminescence mapping further showed that IWO-based stacks delivered more homogeneous emission across the film, a reflection of the electrode’s uniform surface potential distribution.

When translated into complete tandem devices, the gains were immediate. With identical metal grids, IZO-based champion cells achieved a maximum efficiency of 31.65%, with a short-circuit current density of 20.51 mA/cm², an open-circuit voltage of 1.96 V, and a fill factor of 78.74%. Swapping in IWO lifted the champion efficiency to 32.49%, driven primarily by an increase in the fill factor to 79.51%, alongside a modest current rise to 20.74 mA/cm² and a stable voltage of 1.97 V. External quantum efficiency measurements showed that IWO alleviated the current mismatch between the perovskite top sub-cell and the silicon bottom sub-cell, with integrated currents of 21.06 and 20.65 mA/cm² respectively, and improved the photo-response in the near-infrared. Stability testing added further reassurance: after 500 hours of maximum power point tracking under one-sun illumination, unencapsulated IWO devices retained 91.3% of their initial efficiency, compared with only 86.1% for IZO counterparts.

Even with the improved transparent electrode, the fill factor remained below the theoretical limit, and the researchers traced the discrepancy to series resistance from a non-optimized metal grid. Rather than relying on costly trial-and-error fabrication, the team developed a custom simulation program that models how grid geometry affects total power loss. The model incorporates the sheet resistance of the transparent conductive oxide, the width, height, and resistivity of the metal fingers, the grid spacing, and the contact resistance between the oxide and the metal. Crucially, it revealed that while some parameters influence power loss monotonically, finger width and grid spacing behave non-monotonically because of an inherent trade-off: wider, more closely spaced fingers block more sunlight, while narrower, widely spaced fingers force current to travel farther through the resistive oxide layer.

Contour plots of the simulated power loss divided the design space into two regimes. In the high-loss region, increasing grid width and decreasing spacing drove the total loss ratio from 0.2 to 0.7 as shading came to dominate. In the low-loss region, shading and resistive contributions balanced, keeping the loss ratio below 0.1, with the minimum occurring for grid widths below 100 micrometers and spacings below 5 millimeters. The simulations also showed that higher sheet resistance demands tighter grid spacing to shorten lateral transport distances, while the optimal grid width remained fixed at approximately 25 micrometers regardless of the oxide’s sheet resistance—a strikingly universal design rule.

Experimental verification followed. Fabricating tandems with grid widths of 51.09, 92.96, 130.65, and 176.71 micrometers at a fixed spacing, the team watched the short-circuit current decline monotonically as the theoretical shading ratio climbed from 1.52% to 5.15%. Although wider lines slightly improved the fill factor by lowering series resistance, the shading penalty dominated, and overall efficiency fell. The narrowest achievable grid, at 51.09 micrometers, delivered the best performance. Varying the spacing at fixed width told the complementary story: narrowing the spacing from 3.3 to 2.5 millimeters raised shading only modestly, from 1.52% to 2.99%, while substantially boosting the fill factor by shortening the lateral carrier transport distance. The champion device, combining a 50-micrometer grid width with 2.5-millimeter spacing, achieved 33.06% efficiency with a fill factor of 80.87%—the optimal balance point between the two competing loss mechanisms.

The implications reach well beyond the laboratory. The researchers note that industrial metallization techniques such as screen printing, electroplating, and laser transfer printing can already produce metal fingers as narrow as 10 micrometers, meaning the design principles established here translate directly to manufacturing. Challenges remain, including the development of low-temperature curable silver pastes compatible with the perovskite thermal budget, the oxidation susceptibility of cheaper copper-based alternatives, and the corrosive wet chemistry of electroplating routes. On the transparent electrode side, scaling uniform IWO deposition to large areas and reducing dependence on costly indium are flagged as critical next steps. Still, by demonstrating that a humble electrode—long treated as an afterthought—can push tandem cells past the 33% threshold, the study makes a compelling case that the fastest route to cheaper, more efficient solar power may lie in the details hiding in plain sight.

Subject of Research: Front-electrode engineering of perovskite/silicon tandem solar cells to balance shading and resistive losses

Article Title: Balancing Shading and Resistive Losses: 33% Efficient Perovskite/Silicon Tandem Solar Cells via Front‐Electrode Engineering

Article References: Ji, Y., Wang, F., Li, J., Luo, Y., Zhang, H., Liu, Q., Chen, P., Yao, K., Shi, Q., Meng, F., Zhang, L., Yang, C., Liu, J., Liu, Z., Liu, W., & Yu, J. (2026). Balancing Shading and Resistive Losses: 33% Efficient Perovskite/Silicon Tandem Solar Cells via Front‐Electrode Engineering. Advanced Science, Article e78191. https://doi.org/10.1002/advs.78191

Image Credits: AI Generated

DOI: 10.1002/advs.78191

Keywords: perovskite, silicon, tandem solar cells, transparent conductive oxide, IWO, metal grid, fill factor, shading loss, resistive loss, photovoltaics, solar energy efficiency, electrode engineering