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Exploiting intervalley scattering to harness hot carriers in IIIa??V solar cells
摘要： Hot carrier solar cells offer the potential to exceed the Shockley–Queisser limit. So far, however, there has been no clear route to achieve this result. Recently, the exploitation of the satellite valleys of the solar absorber material has been proposed as a feasible approach to harness hot carriers. Here, we show that, upon photoinduced and field-aided intervalley scattering to upper L-valleys, hot carriers can be harnessed in InGaAs/AlInAs heterojunctions at voltages defined by the upper valley (~1.25 V in the ideal case) rather than the bandgap of the InGaAs absorber (0.75 eV) under practical operational conditions. The efficiency of the present system does not exceed the single bandgap limit due to a mismatch in the valley degeneracy across the n+-AlInAs/n-InGaAs interface. However, we suggest that this is not a fundamental limitation to the realization of a hot carrier solar cell.
关键词： InGaAs/AlInAs heterojunctions,hot carrier solar cells,intervalley scattering,valley photovoltaic,Shockley–Queisser limit
更新于2025-09-23 15:19:57
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Tracking solar cell conversion efficiency
摘要： Keeping track of the rapidly improving solar cell performance is not as easy as it might seem. Martin Green describes the Solar Cell Efficiency Tables that have been providing 6-monthly updates of record solar cell performance since the 1990s. Solar cells have become the lowest-cost source of electricity in many countries because their price has dropped dramatically, thanks partly to enhanced energy conversion efficiency, which has improved across all solar cell technologies. For single cells, the efficiency is fundamentally limited by the Shockley–Queisser (SQ) limit of 33.8%, with the well-established GaAs and Si cells the closest to this limit. Particularly rapid progress is evident for perovskite and organic cells. The SQ limit can be exceeded by stacking cells from different materials, each converting part of the solar spectrum. Such multi-junctions already surpassed the SQ limit experimentally in 2009. However, measuring efficiency is more difficult than it might appear, and by the 1980s the solar cell community was calling for the ‘independent confirmation’ of cell results by a recognized test centre. In the 1990s, I started compiling the Solar Cell Efficiency Tables, with the aim of providing an authoritative summary of the progress and encouraging independent confirmation of results — which was a necessary condition for inclusion in the Tables.
关键词： conversion efficiency,independent confirmation,solar cell,multi-junctions,Shockley–Queisser limit
更新于2025-09-19 17:13:59
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Upper limit to the photovoltaic efficiency of imperfect crystals from first principles
摘要： The Shockley-Queisser (SQ) limit provides a convenient metric for predicting light-to-electricity conversion efficiency of a solar cell based on the band gap of the light-absorbing layer. In reality, few materials approach this radiative limit. We develop a formalism and computational method to predict the maximum photovoltaic efficiency of imperfect crystals from first principles. The trap-limited conversion efficiency includes equilibrium populations of native defects, their carrier-capture coefficients, and the associated recombination rates. When applied to kesterite solar cells, we reveal an intrinsic limit of 20% for Cu2ZnSnSe4, which falls far below the SQ limit of 32%. The effects of atomic substitution and extrinsic doping are studied, leading to pathways for an enhanced efficiency of 31%. This approach can be applied to support targeted-materials selection for future solar-energy technologies.
关键词： recombination rates,kesterite solar cells,Shockley-Queisser limit,native defects,carrier-capture coefficients,photovoltaic efficiency
更新于2025-09-19 17:13:59
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New strategies for colloidal-quantum-dot-based intermediate-band solar cells
摘要： The intermediate-band solar cell (IBSC) concept promises to increase the efficiency limit in a single-junction solar cell through the absorption of below-bandgap-energy photons. Despite their operating principle having been proposed over 20 years ago, IBSCs have not delivered on this promise yet, and the devices fabricated so far, mainly based on embedded epitaxial quantum dots, have instead operated with lower efficiency than conventional solar cells. A new paradigm, based on the exploitation as the intermediate band of the intragap states naturally occurring in the density functional theory description of colloidal (i.e., chemically synthesized) quantum dots, was suggested recently. Here, we revisit this intriguing concept unveiling its shortcomings and propose two alternative schemes: in the first, the localized electron surface trap states, ubiquitously found in commonly synthesized colloidal quantum dots, are used as intermediate bands in strongly coupled films made of small InAs nanocrystals and, in the second scheme, the intermediate band is provided by the conduction-band-minimum-derived miniband in films of larger InAs nanocrystals. Both schemes yield estimated limiting IBSC efficiencies exceeding Shockley-Queisser’s limit for a single absorber.
关键词： efficiency,InAs nanocrystals,intermediate-band solar cell,colloidal quantum dots,Shockley-Queisser limit
更新于2025-09-11 14:15:04