Researchers at the Massachusetts Institute of Technology (MIT) have demonstrated a new interface architecture that pushes the traditional silicon solar cell’s efficiency beyond the long-standing single-junction theoretical limit of 29.4%.

The study focused on integrating the singlet exciton fission with crystalline silicon cells through interfacial and device-level engineering. The findings present a promising route to achieving efficiencies of up to 42%, offering a path toward low-cost, high-efficiency solar technology.

Silicon remains the most widely used material for solar cells globally. However, its performance has stagnated near the Shockley–Queisser limit, primarily due to thermalization losses. The Shockley–Queisser limit defines the theoretical maximum efficiency (33%) of a single-junction solar cell.

When high-energy photons strike silicon, the energy exceeding its bandgap is typically lost as heat. This inefficiency limits the number of charge carriers generated per photon and caps the cell’s overall power conversion efficiency.

The MIT research addresses this issue by introducing singlet exciton fission into the silicon photovoltaic workflow. Singlet exciton fission is a photophysical process in which one high-energy photon absorbed by an organic material splits into two triplet excitons. If these excitons can be successfully transferred into the silicon layer, the number of charge carriers produced per photon increases, offering a theoretical quantum efficiency of up to 200%.

The study shows a peak charge generation efficiency of 138% ± 6% for photons absorbed in the tetracene layer, exceeding conventional quantum efficiency limits.

To implement the mechanism, researchers deposited tetracene onto the silicon surface. Tetracene is an organic molecule known for efficient singlet fission.

A critical challenge addressed in this experiment was transferring triplet excitons generated in tetracene into the silicon layer, a task previously hindered by poor interfacial coupling. This challenge was tackled using a multilayer interfacial system, including a hafnium oxynitride layer between tetracene and silicon.

This layer, previously proposed as a mediator, contains defect states near the silicon’s band edge that enable sequential charge transfer rather than the less efficient Dexter transfer mechanism. However, this layer also introduced unwanted mid-gap states that negatively affected silicon photoluminescence.

The Dexter transfer mechanism is a non-radiative energy transfer process between two molecules (donor and acceptor).

To overcome the issues with the transfer mechanism, the interface was further engineered using a donor layer of zinc phthalocyanine (ZnPc), which promotes triplet dissociation and charge separation, and an ultrathin passivating aluminum oxide (AlOx) layer that reduces surface recombination by chemically passivating the silicon’s minute defects, called dangling bonds.

The combination of ZnPc and AlOx provided energy level alignment and electric field passivation, crucial for minimizing recombination losses at the interface. Electric field-effect passivation was found to be especially beneficial for retaining charge carriers transferred from tetracene. These benefits were confirmed by magnetic field-dependent silicon photoluminescence and transient spectroscopy studies.

Multiple device architectures were tested with this interface design. Traditional heterojunction silicon cells showed limited performance improvements due to poor tetracene film morphology. Interdigitated-back-contact cells, which do not efficiently collect surface-generated carriers, also failed to show enhancement from singlet fission.

In contrast, shallow junction planar silicon cells with pyramidal surface texturing and silicon microwire arrays, which are optimized for surface carrier collection, showed significant improvements in photocurrent and external efficiency. These results validate that both interface design and solar cell structure are critical for harvesting the benefits of singlet fission.

The study said the results establish a scalable strategy for integrating organic singlet fission materials with commercial silicon solar technologies. Beyond solar power, the study’s insights could be applied to other silicon-based devices, such as photodetectors and quantum sensors, that require enhanced quantum yields.

This research provides the first clear experimental evidence that singlet exciton fission can be practically coupled with silicon to boost photovoltaic performance.

Recently, a study by the U.S. Department of Energy’s National Renewable Energy Laboratory claimed to have improved perovskite solar cell technology performance by replacing the commonly used fullerene electron transport layer with a newly synthesized ionic salt, commonly referred to as CPMAC.

In December 2024, South Korea-based solar cell and module manufacturer Qcells announced achieving a 28.6% tandem solar cell efficiency on a full-area M10-sized cell that can be scaled for mass manufacturing.

Last March, physicists at the University of Paderborn in Germany, through complex virtual simulations, discovered that adding a thin layer of an organic semiconductor called tetracene to a silicon solar cell can achieve significantly higher efficiency.