🔬 applied physics

External quantum efficiency above 100% in photovoltaic cells due to the technique raising efficiencies for all kinds of solar cells

This study reports that a novel V-shaped module (VSM) technique significantly boosts solar cell power-conversion efficiency and achieves external quantum efficiency above 100% by trapping infrared photons emitted via a mechanism attributed to dark energy.

Original authors: Jianming Li

Published 2026-07-08

📖 4 min read☕ Coffee break read

CC BY 4.0

Original authors: Jianming Li

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

The Big Idea: A Solar "Trap" That Breaks the Rules

Imagine you have a solar panel. Normally, when sunlight hits it, the panel turns some of that light into electricity. But it's not perfect; it reflects some light away (like a mirror) and wastes some energy as heat.

This paper describes a new way to build solar panels using a V-shape (like an open book or a valley). The author, Jianming Li, claims that when you arrange solar cells in this V-shape, they become so efficient at catching light that they produce more electricity than the amount of light hitting them.

In scientific terms, they measured something called "External Quantum Efficiency" (EQE). Usually, this number is below 100% (meaning you get less electricity out than light in). In this experiment, the V-shaped panels hit 140% and even 180%.

How Does It Work? (The "Hall of Mirrors" Analogy)

Think of a flat solar panel like a single wall. If you shine a flashlight at it, some light bounces off and is lost forever.

Now, imagine two walls facing each other at an angle, forming a V.

The Light Trap: When light hits the first wall, some bounces off. But instead of flying away into the sky, it hits the second wall. If it bounces off that one, it might hit the first wall again.
The Bouncing Ball: It's like a ping-pong ball trapped between two paddles. The light bounces back and forth many times inside the "V" until the solar cells finally catch every single photon. This is called "light trapping."

The Mystery: Where Does the Extra Energy Come From?

Here is the surprising part. Even with the light trapping, the math suggests the panels should still be under 100% efficient. But they weren't. They were over 100%.

The paper suggests a "mysterious" source of extra energy: Infrared Light (Heat).

The "Leak": When a solar cell gets hot from the sun, it naturally glows with invisible infrared light (just like a hot stove glows red, but this is invisible heat). Normally, this heat energy just escapes into the air and is wasted.
The "Recycling": In the V-shape, the author claims this escaping heat (infrared light) doesn't leave. Instead, it bounces off the metal backs of the cells and gets trapped inside the V-shape, just like the sunlight did.
The "Magic" Catch: The paper argues that the solar cells have tiny imperfections (defects) inside them. These imperfections act like special hooks that can catch this trapped "heat light" (infrared) and turn it into extra electricity.

The author calls this trapped infrared energy "dark energy." It's not the "dark energy" that expands the universe, but rather a hidden energy source within the panel that is usually ignored.

The Result: A "Free Lunch" for Energy?

Because the V-shape traps both the sunlight and the heat that the panel creates, the cells get a "second bite at the apple."

Step 1: Sunlight hits the cell -> makes electricity.
Step 2: The cell gets hot and emits infrared light.
Step 3: The V-shape traps that infrared light and bounces it back into the cell.
Step 4: The cell catches that infrared light and makes more electricity.

The paper claims this process allows the panel to generate more electrical carriers (electrons) than the number of incoming sunlight photons, resulting in that strange 180% efficiency number.

What Does the Paper Say About the Future?

The paper is very specific about what this technique can do right now based on their findings:

Better Solar Cells: It can significantly boost the efficiency of all kinds of solar cells (thin-film and silicon).
New Detectors: The author suggests this V-shape technique could be used to build special detectors for infrared and ultraviolet light.

Important Note: The paper does not claim this is a commercial product ready for your roof yet, nor does it claim to solve global energy crises immediately. It is a scientific study proposing a new physical explanation for why these V-shaped panels are behaving so strangely, suggesting that "dark energy" (trapped infrared heat) is the key.

Technical Summary: External Quantum Efficiency Above 100% in Photovoltaic Cells via V-Shaped Module Technique

Problem Statement
Traditional photovoltaic (PV) theory suggests that the external quantum efficiency (EQE) of a solar cell cannot exceed 100%, as one absorbed photon typically generates a single electron-hole pair. While Electron-Hole Pair Multiplication (EHPM) has been observed in quantum dot and organic cells, its occurrence in standard polycrystalline silicon cells remains a subject of theoretical constraint. Furthermore, conventional planar solar modules suffer from optical losses due to reflection and the dissipation of excess photon energy as heat, which generates infrared (IR) radiation that is typically lost. The paper addresses the challenge of overcoming these efficiency limits and investigating the physical mechanisms behind a previously observed phenomenon where V-shaped module (VSM) structures significantly boost power-conversion efficiency ( $\eta$ ).

Methodology
The study utilized a V-shaped module (VSM) configuration consisting of two identical, commercially available 1-cm-square polycrystalline silicon solar cells (initial $\eta$ of 13.4%) placed at an angle ( $\alpha$ ) relative to each other. The researchers systematically investigated the EQE of these cells using a spectral response measuring equipment (Model CEP-25/CH). Measurements were conducted at four specific opening angles: $20^\circ$ , $30^\circ$ , $40^\circ$ , and $180^\circ$ (the latter serving as a planar control). The study involved measuring individual cells as well as cells connected in parallel to ensure reproducibility and consistency. The experimental protocol included rigorous verification steps to ensure data reliability, with measurement errors maintained below 2%.

Key Contributions and Results
The primary contribution of this work is the experimental observation of EQE values exceeding 100% in standard polycrystalline silicon solar cells when arranged in a VSM configuration.

Quantitative Results: At an opening angle of $\alpha = 30^\circ$ , the peak EQE reached 1.4 (140%). At $\alpha = 20^\circ$ , the peak EQE surged to 1.8 (180%). In contrast, the planar configuration ( $\alpha = 180^\circ$ ) exhibited a peak EQE of approximately 0.8.
Reproducibility: The results were consistent across both individual cells and parallel connections, and the phenomenon was easily reproducible.
Mechanism Analysis: The authors attribute the efficiency gains to two main factors:
1. Optical Trapping: The V-geometry creates multiple internal reflections, significantly reducing reflection losses and enhancing photon absorption compared to planar cells.
2. Infrared Recycling and Sub-band-gap Excitation: The study proposes that the VSM traps not only incident sunlight but also IR photons emitted by the cells themselves (thermal radiation). These trapped IR photons are re-absorbed via defect energy levels within the bandgap (specifically at grain boundaries in polycrystalline silicon). This process, termed sub-band-gap excitation, generates additional photoexcited carriers, theoretically enabling EHPM events in silicon cells.

Significance and Claims
The paper claims that the VSM technique offers a new avenue for studying photovoltaic physics by challenging traditional concepts regarding efficiency limits. The authors posit that the "surprising" VSM effect, characterized by EQE > 100%, is explainable through the trapping of emitted IR photons (referred to in the text as "dark energy") which are then converted into extra carriers via defect-mediated absorption.

The study concludes that this mechanism provides new evidence for the hypothesis that non-infrared light incident on a VSM cell can lead to IR emission, which subsequently creates extra carriers in the facing cell. Additionally, the authors suggest that the VSM technique could be utilized to develop photodetectors specifically for infrared and ultraviolet light. The work asserts that these findings support the viewpoint that IR-photocurrent in semiconductor devices can be generated through sub-band-gap excitation, potentially offering new insights into the interpretation of ohmic contacts and tunneling diodes.

The Big Idea: A Solar "Trap" That Breaks the Rules

How Does It Work? (The "Hall of Mirrors" Analogy)

The Mystery: Where Does the Extra Energy Come From?

The Result: A "Free Lunch" for Energy?

What Does the Paper Say About the Future?

More like this