arXiv subjects

Murad J. Y. Tayebjee

Publications and source records attributed to Murad J. Y. Tayebjee.

6 recordsLinked to original sources

arXiv2026

Combined photoluminescence and electrical characterization of valley photovoltaic devices explained with an equivalent circuit

We present an equivalent-circuit analysis that simultaneously considers the photoluminescence and electrical responses of valley photovoltaic devices. Valley photovoltaics (VPV) are a novel concept for hot-carrier solar cells, where intervalley scattering of electrons in the absorbing material helps maintain the conduction-band electron populations at metastable satellite valleys, which are at energies higher than the conduction-band minimum. We measure intensity- and voltage-dependent photoluminescence and electrical signals of a VPV device, which has previously shown S-shaped current-voltage characteristics and thus low efficiency. We present an equivalent circuit that captures the S-shaped current-voltage curves and simultaneously describes our photoluminescence and electric measurements. The equivalent-circuit model indicates that a reverse diode causes inefficient extraction of electrons and thus the S shape. We use a Poisson/drift-diffusion model to demonstrate that the reverse diode can be either explained by the valley-scattering process itself or a heterojunction barrier. The reverse diode must be eliminated before VPV devices can achieve high efficiency.

physics.app-ph↗

arXiv2026

Silicon Solar Cell Design for >30% Efficiency via Singlet Fission

Singlet fission (SF) materials convert high-energy photons into multiple charge carriers, providing a route to exceed the efficiency limits of single-junction silicon solar cells without many of the complexities of multi-junction tandem designs. Following the first demonstration of an SF-enhanced silicon solar cell in 2025, there is a need to understand how SF materials can be effectively integrated into high-efficiency industrial silicon devices and translated from proof of concept to a manufacturable technology. Using coupled optical and electrical simulations, we assess the efficiency potential of several industrially relevant silicon cell architectures combined with SF materials. Interdigitated back-contact (IBC) cells offer the greatest potential for improvement due to unrestricted front-surface access and can achieve efficiencies exceeding 33%. However, performance is highly sensitive to front-surface passivation quality. Appropriate silicon design, particularly controlled surface doping and fixed interfacial charge, can mitigate recombination losses and relax passivation requirements for ultra-thin exciton-transfer layers.

cond-mat.mtrl-sci↗

arXiv2026

Visible Imaging of Incoherent 1200-nm Light via Triplet--Triplet Annihilation Upconversion

Upconversion of low-energy photons to higher-energy photons provides an opportunity to surpass traditional limitations in fields such as 3D printing, photovoltaics, and photocatalysis. Triplet--triplet annihilation upconversion (TTA-UC) is particularly appealing for such applications as it can efficiently upconvert low-intensity, incoherent light. However, previously demonstrated thin-film TTA systems are simultaneously constrained by modest efficiencies and limited reach into the near infrared (NIR). Here, we design a single-layer thin-film bulk heterojunction that integrates PbS quantum dots (QDs) as tunable NIR absorbers within an organic semiconductor matrix of TES-ADT, achieving large anti-Stokes shifts up to 500 nm and high internal quantum efficiencies across the NIR-I and NIR-II windows (800-1200 nm). Through the incorporation of 5-tetracene carboxylic acid ligands on the PbS QD surface, the yield of sensitized triplets was boosted, as confirmed by transient absorption and time-resolved photoluminescence measurements. The resulting films demonstrated a 15-fold improvement in UC efficiency. Furthermore, we demonstrate visible imaging of incoherent 1200 nm light via thin-film TTA-UC at incident intensities at the imaging mask as low as 20 mWcm$^2$, marking a significant advance toward practical implementation of solid-state NIR-to-visible upconversion.

physics.optics↗

arXiv2022

Quintet formation and exchange fluctuations: The role of stochastic resonance in singlet fission

Singlet fission describes the spin-conserving production of two triplet excitons from one singlet exciton. The existence of a spin-2 (quintet) triplet-pair state as a product of singlet fission is well established in the literature, and control of quintet formation is an important step towards applying singlet fission in photovoltaics and quantum information. However, a definitive mechanism for quintet formation is yet to be established, which makes it difficult to design materials for optimal quintet formation. Here we outline a mechanism in which inter-triplet exchange coupling fluctuations drive fast and efficient quintet formation. In contrast with conventional wisdom, we show that quintet population can arise despite strong exchange coupling. We evaluate the performance of this quintet formation mechanism in two regimes of conformational freedom, and relate quintet dynamics to material properties of singlet fission molecules.

cond-mat.mes-hall↗

arXiv2022

Singlet Fission Photovoltaics: Progress and Promising Pathways

Singlet fission is a form of multiple exciton generation which occurs in organic chromophores when a high energy singlet exciton separates into two lower energy triplet excitons, each with approximately half the singlet energy. Since this process is spin-allowed it can proceed on an ultrafast timescale of less than several picoseconds, outcompeting most other loss mechanisms and reaching quantitative yields approaching 200%. Due to this high quantum efficiency, the singlet fission process shows promise as a means of reducing thermalisation losses in photovoltaic cells. This would potentially allow for efficiency improvements beyond the thermodynamic limit in a single junction cell. Efforts to incorporate this process into solar photovoltaic cells have spanned a wide range of device structures over the past decade. In this review we compare and categorise these attempts in order to assess the state of the field and identify the most promising avenues of future research and development.

physics.app-ph↗

arXiv2019

Fluctuating exchange interactions enable quintet multiexciton formation in singlet fission

Several recent electron spin resonance studies have observed a quintet multiexciton state during the singlet fission process. Here we provide a general theoretical explanation for the generation of this state by invoking a time-varying exchange coupling between pairs of triplet excitons, and subsequently solving the relevant time-varying spin Hamiltonian for a range of transition times. We simulate experimental ESR spectra and draw qualitative conclusions about the adiabatic/diabatic transition between triplet pair spin states.

cond-mat.mtrl-sci↗