Optimización numérica de la fotocorriente en celdas solares tandem de perovskitas/silicio

El constante aumento de la eficiencia de las celdas solares de silicio ha convertido la generación fotovoltaica en una fuente de energía competitiva. Sin embargo la eficiencia récord de estas celdas se encuentra ya muy cercana al límite teórico y por ello se ha propuesto preparar celdas tandem combinando celdas de silicio con celdas de perovskitas orgánicas-inorgánicas. Estas últimas celdas tienen altas eficiencias, bajos costos de fabricación y son compatibles con la tecnología del silicio. En este trabajo, aplicamos un modelo óptico para optimizar los materiales de las capas de contacto de la celda tandem así como los espesores de las capas involucradas. Las simulaciones nos permiten identificar y cuantificar las pérdidas ópticas asociadas a la reflexión y absorción en las capas funcionales. El algoritmo de optimización nos permitió aumentar la fotocorriente hasta un 7% respecto de las celdas reportadas en la literatura.The steady increase in silicon solar cells efficiency over the last 40 years has turned photovoltaics into a competitive energy source. However, the achieved efficiency record is already close to the theoretical limit and therefore new approaches are needed to overcome this limit. It has been suggested that combining silicon cells and inorganic-organic perovskite cells in tandem configuration should further increase the device efficiency. Perovskite cells have high efficiency, low fabrication costs and they are compatible with silicon technology. In this work, we apply an optical model to optimize the functional and active layers of state-of-the-art perovskite/silicon tandem cells. The simulation results allow us to identify and quantify the optical losses associated to reflection and absorption in contact layers. With the aid of an optimization algorithm the photocurrent increased up to 7% relative to the photocurrent of tandem cells reported in the literature.Tema 4: Energía solar, conversión fotovoltaica.Facultad de Arquitectura y Urbanism

Optimización numérica de la fotocorriente en celdas solares tandem de perovskitas/silicio

El constante aumento de la eficiencia de las celdas solares de silicio ha convertido la generación fotovoltaica en una fuente de energía competitiva. Sin embargo la eficiencia récord de estas celdas se encuentra ya muy cercana al límite teórico y por ello se ha propuesto preparar celdas tandem combinando celdas de silicio con celdas de perovskitas orgánicas-inorgánicas. Estas últimas celdas tienen altas eficiencias, bajos costos de fabricación y son compatibles con la tecnología del silicio. En este trabajo, aplicamos un modelo óptico para optimizar los materiales de las capas de contacto de la celda tandem así como los espesores de las capas involucradas. Las simulaciones nos permiten identificar y cuantificar las pérdidas ópticas asociadas a la reflexión y absorción en las capas funcionales. El algoritmo de optimización nos permitió aumentar la fotocorriente hasta un 7% respecto de las celdas reportadas en la literatura.The steady increase in silicon solar cells efficiency over the last 40 years has turned photovoltaics into a competitive energy source. However, the achieved efficiency record is already close to the theoretical limit and therefore new approaches are needed to overcome this limit. It has been suggested that combining silicon cells and inorganic-organic perovskite cells in tandem configuration should further increase the device efficiency. Perovskite cells have high efficiency, low fabrication costs and they are compatible with silicon technology. In this work, we apply an optical model to optimize the functional and active layers of state-of-the-art perovskite/silicon tandem cells. The simulation results allow us to identify and quantify the optical losses associated to reflection and absorption in contact layers. With the aid of an optimization algorithm the photocurrent increased up to 7% relative to the photocurrent of tandem cells reported in the literature.Tema 4: Energía solar, conversión fotovoltaica.Facultad de Arquitectura y Urbanism

Optimización numérica de la fotocorriente en celdas solares tandem de perovskitas/silicio

El constante aumento de la eficiencia de las celdas solares de silicio ha convertido la generación fotovoltaica en una fuente de energía competitiva. Sin embargo la eficiencia récord de estas celdas se encuentra ya muy cercana al límite teórico y por ello se ha propuesto preparar celdas tandem combinando celdas de silicio con celdas de perovskitas orgánicas-inorgánicas. Estas últimas celdas tienen altas eficiencias, bajos costos de fabricación y son compatibles con la tecnología del silicio. En este trabajo, aplicamos un modelo óptico para optimizar los materiales de las capas de contacto de la celda tandem así como los espesores de las capas involucradas. Las simulaciones nos permiten identificar y cuantificar las pérdidas ópticas asociadas a la reflexión y absorción en las capas funcionales. El algoritmo de optimización nos permitió aumentar la fotocorriente hasta un 7% respecto de las celdas reportadas en la literatura.The steady increase in silicon solar cells efficiency over the last 40 years has turned photovoltaics into a competitive energy source. However, the achieved efficiency record is already close to the theoretical limit and therefore new approaches are needed to overcome this limit. It has been suggested that combining silicon cells and inorganic-organic perovskite cells in tandem configuration should further increase the device efficiency. Perovskite cells have high efficiency, low fabrication costs and they are compatible with silicon technology. In this work, we apply an optical model to optimize the functional and active layers of state-of-the-art perovskite/silicon tandem cells. The simulation results allow us to identify and quantify the optical losses associated to reflection and absorption in contact layers. With the aid of an optimization algorithm the photocurrent increased up to 7% relative to the photocurrent of tandem cells reported in the literature.Tema 4: Energía solar, conversión fotovoltaica.Facultad de Arquitectura y Urbanism

Microscopic origins of performance losses in highly efficient Cu In, Ga Se2 thin film solar cells

Thin film solar cells based on polycrystalline absorbers have reached very high conversion efficiencies of up to 23 25 . In order to elucidate the limiting factors that need to be overcome for even higher efficiency levels, it is essential to investigate microscopic origins of loss mechanisms in these devices. In the present work, a high efficiency 21 without anti reflection coating copper indium gallium diselenide CIGSe solar cell is characterized by means of a correlative microscopy approach and corroborated by means of photoluminescence spectroscopy. The values obtained by the experimental characterization are used as input parameters for two dimensional device simulations, for which a real microstructure was used. It can be shown that electrostatic potential and lifetime fluctuations exhibit no substantial impact on the device performance. In contrast, nonradiative recombination at random grain boundaries can be identified as a significant loss mechanism for CIGSe solar cells, even for devices at a very high performance leve

Mobility dependent efficiencies of organic bulk heterojunction solar cells: Surface recombination and charge transfer state distribution

Recent simulations of the efficiency of polymer/fullerene solar cells as a function of mobility predicted finite optimum mobilities due to a decrease in open circuit voltage for higher mobilities. We explain this decrease in open circuit voltage with two features of the commonly used model, namely, infinite surface recombination and an integration over a distribution of separation distances of electron and hole in a charge transfer state at the interface between donor and acceptor molecules. Especially, the assumption of a variable electron/hole pair separation at the interface has a considerable influence on the open circuit voltage

Numerical simulation of carrier collection and recombination at grain boundaries in Cu(In,Ga)Se-2 solar cells

Two-dimensional numerical device simulations investigate the influence of grain boundaries (GBs) on the performance of Cu(In,Ga)Se-2 solar cells. We find that the electronic activity of grain boundaries can reduce the efficiency of Cu(In,Ga)Se-2 solar cells from 20% to below 12% making proper passivation of GBs a primary requirement for high efficiency. Cell efficiencies larger than 19% require GB defect densities below 10(11) cm(-2). Also, an internal band offset in the valence band due to a Cu-poor region adjacent to the GBs could effectively passivate grain boundaries that are otherwise very recombination active. It is shown that such a barrier must be more than 300 meV high and at least 3 nm wide to virtually suppress all grain boundary recombination. Contrariwise, such a barrier represents an obstacle for hole transport reducing carrier collection across grain boundaries that are not perpendicular to the cell surface. We further find that inverted grain boundaries lead to an accumulation of the short circuit current along the grain boundary, which in certain situations enhances the total short circuit current. However, we do not find any beneficial effect of any type of grain boundaries on the overall cell efficiency. (C) 2008 American Institute of Physics

Efficiency Limits of Organic Bulk Heterojunction Solar Cells

We calculate the radiative efficiency limits of organic bulk heterojunction solar cells according to the theory of Shockley and Queisser and compare the results with experimental device performance. The difference between limiting theory (23% power conversion efficiency) and experimental data (4%) is explained and quantified by five reasons, namely the energy level misalignment at the donor/acceptor heterointerface of the bulk heterojunction, insufficient light trapping, low exciton diffusion lengths, nonradiative recombination, and low charge carrier mobilities. Comparison of the impact of the different loss mechanisms by numerical simulation reveals that efficiencies above 10% using PF10TBT/PCBM blends will require mostly a strong reduction of nonradiative recombination. The energy misalignment and the low carrier mobilities appear as a second-order restriction in this type of blend