Key Takeaways & Executive Findings
- •• • PO-TSCs have achieved certified efficiencies exceeding 26%, with theoretical limits beyond 40% for dual-junction designs, indicating a clear pathway to surpass single-junction S-Q limits. • • Wide-bandgap perovskite top cells require precise defect and phase control to minimize voltage losses; surface passivation using isomeric diammonium molecules has been shown to reduce non-radiative recombination, enabling open-circuit voltages exceeding 2.2 V in tandem devices. • • Interconnecting layers must be optically transparent and electrically efficient; solution-processed interconnects have demonstrated reduced carrier recombination, with a certified efficiency of 25.1% achieved via bottom contact modulation in inorganic perovskite/organic tandems. • • Organic bottom cells benefit from enhanced charge generation and collection; Knoevenagel condensation enables high-dipole interfacial molecules that improve charge extraction, contributing to overall efficiency gains and operational stability.
Abstract
Perovskite/organic tandem solar cells (PO-TSCs) have emerged as a compelling photovoltaic architecture to transcend the Shockley-Queisser limit of single-junction devices. By monolithically stacking a wide-bandgap (WBG) perovskite top cell and a narrow-bandgap (NBG) organic bottom cell, PO-TSCs enable broad spectral utilization and reduced thermalization loss, offering a viable pathway toward efficiencies beyond 30%. Their solution processability, compatibility with orthogonal solvents, and potential for lightweight, flexible, and semi-transparent modules further make them attractive for building integrated and portable electronics. However, the realization of high-performance PO-TSCs critically depends on precise carrier regulation across the entire multilayer stack, where inefficient charge transport, recombination losses, and interfacial bottlenecks often limit the overall power conversion efficiency (PCE) and stability. This review systematically examines the carrier-regulation strategies essential for advancing PO-TSCs, focusing on defect and phase-control in WBG perovskites, the design of optically transparent and electrically efficient interconnecting layers, and the enhancement of charge generation and collection in organic subcells. The integration of these approaches has recently enabled efficiencies exceeding 26%, demonstrating the rapid progress of the field. Ultimately, we conclude with an outlook on the remaining challenges in scalability, operational stability, and manufacturability, providing a roadmap for future research toward commercially viable tandem photovoltaics.
1. Introduction
Single-junction perovskite solar cells (pero-SCs) have reached certified power conversion efficiencies (PCEs) surpassing 27%, and organic solar cells (OSCs) have achieved notable efficiencies above 21%. Despite these advances, any single-junction device is intrinsically limited by the Shockley-Queisser (S-Q) thermodynamic boundary, which caps achievable photocurrent and voltage due to sub-bandgap photon transmission and above-bandgap thermalization losses. This fundamental ceiling necessitates alternative architectures to utilize a greater fraction of the solar spectrum and mitigate thermalization losses.
Tandem solar cells (TSCs) address this bottleneck by monolithically integrating two subcells with complementary bandgaps. The wide-bandgap (WBG) top cell absorbs high-energy photons, while the narrow-bandgap (NBG) bottom cell captures lower-energy photons, enabling broader spectral utilization and reduced thermalization loss. Among various TSC configurations, perovskite/organic tandem solar cells (PO-TSCs) offer distinct advantages: solution processability, compatibility with orthogonal solvents, and potential for lightweight, flexible, and semi-transparent modules. However, achieving high performance critically depends on precise carrier regulation across the multilayer stack, where inefficient charge transport, recombination losses, and interfacial bottlenecks often limit PCE and stability. This review systematically examines carrier-regulation strategies essential for advancing PO-TSCs, focusing on defect and phase control in WBG perovskites, design of optically transparent and electrically efficient interconnecting layers, and enhancement of charge generation and collection in organic subcells. Recent integration of these approaches has enabled efficiencies exceeding 26%, demonstrating rapid progress and providing a roadmap toward commercially viable tandem photovoltaics.
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WANG Ziyue, CHEN Weijie, LI Yaowen (2026). Carrier Regulation in Monolithic Perovskite/Organic Tandem Solar Cells. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-026-4106-8
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Frequently Asked Questions
What are the primary failure mechanisms limiting the operational stability of perovskite/organic tandem solar cells under prolonged illumination and thermal stress?
Operational stability is primarily compromised by ion migration in the perovskite subcell, which induces phase segregation and interfacial degradation. Additionally, the organic bottom cell is susceptible to photo-oxidation and morphological instability. Recent studies have shown that surface passivation using isomeric diammonium molecules can mitigate non-radiative recombination and improve stability, but long-term data under damp heat and UV exposure are still lacking. For instance, devices with certified efficiency of 25.1% have been reported, but their stability under 1000 hours of continuous operation at 85°C and 85% relative humidity has not been fully disclosed.
How does the interconnecting layer (ICL) design influence charge recombination and series resistance in monolithic PO-TSCs, and what are the optimal material combinations?
The ICL must be optically transparent and electrically efficient to minimize parasitic absorption and series resistance. Solution-processed interconnects have demonstrated reduced carrier recombination, as evidenced by improved fill factors and open-circuit voltages. For example, a certified efficiency of 25.1% was achieved via bottom contact modulation in inorganic perovskite/organic tandems, highlighting the importance of contact engineering. Optimal ICLs often employ a combination of a hole-transport layer (e.g., PEDOT:PSS or NiOx) and an electron-transport layer (e.g., SnO2 or ZnO), with a thin metal or conductive oxide recombination layer. The choice of materials must ensure orthogonal solvent compatibility to avoid damaging underlying layers.
What are the scalability bottlenecks for roll-to-roll manufacturing of PO-TSCs, and what cost per watt can be projected?
Scalability is hindered by the use of lab-scale spin-coating methods and the need for precise thickness control of multiple layers. Roll-to-roll processing requires slot-die coating or inkjet printing, which demand formulation of inks with appropriate rheology and solvent systems. Additionally, the interconnecting layer deposition must be compatible with high-throughput processes. Cost projections are speculative, but given the low material costs of organic semiconductors and perovskite precursors, a levelized cost of electricity (LCOE) below $0.05/kWh is conceivable if module efficiencies exceed 25% and lifetimes reach 20 years. However, current certified efficiencies are only for small-area cells (typically <1 cm²), and scaling to module sizes often results in efficiency losses due to series resistance and non-uniform coating.
How do wide-bandgap perovskite top cells mitigate voltage losses due to halide phase segregation, and what passivation strategies have proven most effective?
Halide phase segregation in mixed-halide perovskites (e.g., Cs0.2FA0.8Pb(I0.8Br0.2)3) leads to the formation of iodide-rich domains, which reduce the bandgap and cause voltage losses. Passivation strategies include the use of isomeric diammonium molecules that coordinate with undercoordinated lead ions and suppress halide migration. For instance, Jiang et al. (Nature, 2024) demonstrated that isomeric diammonium passivation reduces non-radiative recombination and improves open-circuit voltage. Additionally, surface reconstruction via post-treatment with organic halide salts has been shown to heal surface defects. These approaches have enabled open-circuit voltages exceeding 2.2 V in tandem devices, as reported by Son et al. (Adv. Energy Mater., 2025).
What are the specific challenges in achieving high current matching between the WBG perovskite top cell and NBG organic bottom cell, and how can they be addressed?
Current matching requires precise tuning of the thickness and bandgap of each subcell to ensure equal photocurrent generation. The WBG perovskite typically has a bandgap of ~1.8 eV, while the NBG organic absorber has a bandgap of ~1.2–1.4 eV. Challenges include parasitic absorption in the interconnecting layer and non-ideal transmission of sub-bandgap photons. To address this, the ICL must be highly transparent, and the organic bottom cell must have a broad absorption spectrum. Recent advances in non-fullerene acceptors have extended the absorption edge to ~1000 nm, improving current generation. Additionally, optical modeling is used to optimize layer thicknesses. For example, efficiencies exceeding 26% have been achieved by balancing photocurrents, as reported in the review.
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