Scientists Discover Way to Exceed Longstanding Solar Power Limits

2026-09-27 green

Groningen, Sunday, 27 September 2026.
Researchers discovered that tin-based solar cells retain energy 1,000 times longer than standard materials, offering a breakthrough path to surpass the traditional 33% solar efficiency limit.

Unlocking the Physics of Hot Carriers

A collaborative research effort between scientists at the University of Groningen in the Netherlands and TU Wien in Austria has unveiled the physical mechanisms behind unusually long-lived “hot carriers” in tin-based perovskite materials [4][5][6]. Published in the journal ACS Energy Letters in September 2026 [8], the study focuses on caesium tin iodide (CsSnI₃), a lead-free crystalline semiconductor that could redefine the efficiency limits of photovoltaic technology [1][4][5]. Normally, when solar photons strike a conventional cell with excess energy, they generate “hot electrons” [2]. In standard silicon cells, this surplus energy is almost instantaneously dissipated as waste heat, cooling down within a few picoseconds [2][8].

The Dual-Action Mechanism Behind the Delay

The Groningen and TU Wien researchers discovered that in tin-based perovskites, these hot electrons retain their high-energy state for nanoseconds rather than picoseconds—representing a lifespan extension of roughly 1,000 times [2][4][8]. Through advanced ensemble Monte Carlo simulations and time-resolved photoluminescence measurements, the team identified that this delay is caused by two overlapping phenomena: the “hot phonon bottleneck” and the dynamic “Burstein-Moss effect” (band filling) [1][4][5]. When active together, these mechanisms prevent the excited electrons from rapidly shedding their energy [4][5]. Individually, neither effect is sufficient to explain the prolonged cooling times, but together they create a powerful synergy [4].

Quantifying the Heat Retention

The thermodynamic retention achieved by this material is remarkable. Under computer simulations of CsSnI₃ at a carrier density of 3×10¹⁸ cm⁻³, disabling these dual effects resulted in a rapid carrier cooling time of approximately 4 picoseconds [4][5][6]. However, when both the hot phonon bottleneck and the Burstein-Moss effect were active, the simulated cooling time stretched to about 470 picoseconds, showing an increase of 117.5 times [4][5][6]. This closely matches earlier physical measurements of CsSnI₃, which documented a slow cooling component of approximately 636 picoseconds [4][5][6]. During this extended cooling phase, carriers remained genuinely “hot” at temperatures above 600 K for at least 200 picoseconds following excitation, which is crucial for achieving a theoretical voltage boost in hot-carrier solar cells [4].

Designing Sustainable Solar Technology

Led by Jan Anton Koster, Professor of Physics of Novel Semiconductors and Devices, and Professor Maria Antonietta Loi at the University of Groningen, the research team admitted that the initial experimental results were so unexpected that they initially doubted their own measurements [1][4][8]. To guide future engineering, the team, which also included PhD student Tim Faber, outlined three key design criteria for building high-efficiency hot-carrier absorbers: utilizing materials with a low effective carrier mass (which favors tin over toxic lead compositions), ensuring a soft crystal lattice with low-frequency optical modes to facilitate the phonon bottleneck, and maintaining high material purity to prevent defects from accelerating carrier cooling [4][5][6][8].

The Path and Hurdles to Commercialization

Despite the promise of bypassing the traditional 33% Shockley-Queisser efficiency limit for single-junction solar cells, the technology remains in the fundamental materials-physics stage [2][5][6]. No commercial-scale production or working prototypes of these hot-carrier devices are currently available [1][2][6]. The primary challenge moving forward is developing a practical method to rapidly and selectively extract these energetic carriers into an external circuit before they eventually cool down [2][5][6][8]. Nevertheless, by identifying the exact physics behind the energy retention of tin-based perovskites, researchers have successfully cleared one of the most significant theoretical barriers to next-generation green energy [2].

Bronnen

perovskite photovoltaics solar efficiency