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

Hybrid solar cells of this kind sit at the intersection of two very different material worlds. Organic photovoltaics, built from polymers and small molecules, are inexpensive, lightweight and mechanically flexible, but they suffer from narrow band gaps that encourage rapid charge recombination and limit photocurrent. Inorganic semiconductors, by contrast, offer excellent charge transport and robust light absorption, though at higher fabrication cost. Combining the two promises the best of both, provided the interface between the polymer and the semiconductor can be engineered to separate and transfer photoexcited charges efficiently. PANI has long been a favorite for this role. In its doped, conductive emeraldine salt form it behaves as a p-type conductor, and acid doping shrinks its optical band gap from roughly 3.06 electron volts in the undoped emeraldine base to around 2.35 to 2.54 electron volts, making it far more useful as a light-absorbing, charge-transfer layer. Paired against n-type substrates, it forms the p-n style heterojunction at the heart of the devices in this study.

The choice of inorganic partner matters enormously. Gallium arsenide is a III-V direct-band-gap semiconductor with a gap of 1.42 electron volts, a property that allows it to absorb photons efficiently and to boast high electron mobility. Silicon, the workhorse of photovoltaics, has an indirect band gap of about 1.1 electron volts, which makes absorption less efficient per unit thickness. But the Zakho team’s earlier work had already hinted that something subtler was also at play. Previous studies by co-author Dler A. Jameel and colleagues found that PANI devices on (311)A and (311)B n-GaAs substrates outperformed those on (100) GaAs, with differences in open-circuit voltage, fill factor and rectification ratio attributable to orientation-dependent interface quality, defect densities and charge transport. The new study extends that logic into a direct GaAs-versus-silicon comparison, a combination the authors describe as previously unexamined.

The fabrication itself was deliberately simple, underscoring the practical relevance of the findings. Chemically synthesized PANI was spin-coated at 2000 revolutions per minute onto each of the three substrates, which had been cleaned with deionized water and acetone and dried under nitrogen gas. Current-voltage measurements were then performed at room temperature with a Keithley 2450 source meter, both in darkness and under illumination of 60 milliwatts per square centimeter. From the illuminated current density-voltage curves the team extracted the standard photovoltaic figures of merit: open-circuit voltage, short-circuit current density, fill factor and power conversion efficiency. From the dark measurements, analyzed with the thermionic emission model, they derived the diode parameters, including saturation current, barrier height, ideality factor, series resistance and rectification ratio.

Under illumination, the PANI/(111)B n-GaAs device led on nearly every measure. Its open-circuit voltage of 129 millivolts topped the 110 millivolts of the PANI/(100) n-Si device and the 95 millivolts of the PANI/(111) n-Si device, and its short-circuit current density of 10.8 milliamperes per square centimeter edged out 10.1 for (111) silicon and well above 7.93 for (100) silicon. Fill factors clustered tightly, at 36 percent for the GaAs device against 35 and 37 percent for the two silicon orientations. The decisive margin came in conversion efficiency: 0.83 x 10^-3 percent for the GaAs heterostructure, versus 0.59 x 10^-3 percent for PANI/(111) n-Si and 0.51 x 10^-3 percent for PANI/(100) n-Si. The team attributes the GaAs advantage primarily to its direct band gap, which generates photocarriers more efficiently than indirect-gap silicon, combined with favorable charge separation and transport at the (111)B interface.

The numbers, the authors are careful to note, remain modest compared with the best hybrid devices reported elsewhere. Open-circuit voltages of 342 millivolts on PANI/(311)B n-GaAs and 400 millivolts on PANI/n-Si have appeared in prior literature, and the low values here likely reflect higher interface recombination or differences in film quality and polymer-semiconductor interaction. But the relative rankings are the point. When illuminated performance was set against dark-rectification behavior, a striking inversion emerged: the material that made the better solar cell was not the material that made the better diode. Photovoltaic output, the study concludes, is governed chiefly by the bulk optical properties of the semiconductor, while diode quality is governed chiefly by the quality of the interface, and those two qualities do not necessarily reside in the same substrate.

Dark current-voltage analysis told the second half of the story. The PANI/(111) n-Si device posted the best diode parameters of the trio: a rectification ratio of 50.20 at plus and minus one volt, dwarfing 3.98 for PANI/(100) n-Si and 1.43 for PANI/(111)B n-GaAs, alongside the highest barrier height at 0.69 electron volts and the lowest ideality factor at 3.07. Its saturation current, 2.11 x 10^-7 amperes, was also the smallest of the three. Because an ideal diode has an ideality factor of one, all three devices deviate substantially from ideal behavior, a hallmark of organic-inorganic Schottky junctions where interface states and recombination within the polymer dominate charge transport. Even so, the silicon (111) device comes closest to the ideal, which the authors attribute to a junction with fewer recombination pathways. The (100) silicon device, by contrast, showed a saturation current roughly an order of magnitude higher than its rivals, suggesting greater carrier injection and recombination at that orientation.

Turn-on voltages added further texture. The GaAs device began conducting at the lowest bias, 0.52 volts, indicating easier carrier injection at the junction, while (100) and (111) silicon required 0.58 and 0.63 volts respectively. Series resistance followed the same pattern: 0.35 kilo-ohms for the GaAs device, helped by GaAs’s higher carrier mobility, against 0.81 and 0.37 kilo-ohms for the (100) and (111) silicon devices. Larger barrier heights, the authors note, generally correspond to fewer interface defects and reduced recombination, which is precisely what the silicon (111) interface appears to deliver under dark conditions. The comparison with earlier GaAs studies is instructive: the 0.59 electron-volt barrier on (111)B GaAs sits above the 0.45 electron volts reported for (110) GaAs but below the 0.75 and 0.79 electron volts seen on (100) and (311)B orientations, reinforcing that orientation tunes the barrier landscape in ways that are neither trivial nor predictable from band gaps alone.

The broader implication is that substrate selection in hybrid photovoltaics is a two-dimensional optimization problem. If the goal is light harvesting, the bulk optical properties of the semiconductor, here GaAs’s direct gap, dominate the outcome, and the (111)B GaAs orientation additionally promotes efficient charge separation. If the goal is a rectifying junction, say for photodetectors or diode applications, interface quality takes precedence, and silicon’s (111) plane delivers the cleanest, most rectifying PANI contact measured here. For a field searching for efficiency gains through interface engineering, molecular doping and nanostructuring, the message is that the crystallographic fingerprint of the substrate is not a detail to be controlled for; it is a design variable in its own right. As flexible, solution-processed hybrid devices edge toward real applications, the authors’ systematic comparison suggests that choosing the right crystal face could matter as much as choosing the right material.

Subject of Research: Effects of substrate type and crystallographic orientation on the photovoltaic and diode performance of PANI-based organic/inorganic hybrid solar cell devices.

Article Title: Effects of substrate type and orientation on the photovoltaic and diode performance of PANI-Based organic/inorganic hybrid devices

Article References: Tatar, H. H., & Jameel, D. A. (2026). Effects of substrate type and orientation on the photovoltaic and diode performance of PANI-Based organic/inorganic hybrid devices. Journal of Materials Science: Polymers, 1(1), Article 12. https://doi.org/10.1007/s44493-026-00012-7

Image Credits: AI Generated

DOI: 10.1007/s44493-026-00012-7

Keywords: hybrid solar cells, polyaniline, PANI, GaAs, silicon, substrate orientation, heterojunction, photovoltaics, open-circuit voltage, fill factor, barrier height, ideality factor