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23.6%-efficient monolithic perovskite/silicon tandem solar cells with improved stability

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As the record single-junction efficiencies of perovskite solar cells now rival those of copper indium gallium selenide, cadmium telluride and multicrystalline silicon, they are becoming increasingly attractive for use in tandem solar cells due to their wide, tunable bandgap and solution processability. Previously, perovskite/silicon tandems were limited by significant parasitic absorption and poor environmental stability. Here, we improve the efficiency of monolithic, two-terminal, 1-cm2 perovskite/silicon tandems to 23.6% by combining an infrared-tuned silicon heterojunction bottom cell with the recently developed caesium formamidinium lead halide perovskite. This more-stable perovskite tolerates deposition of a tin oxide buffer layer via atomic layer deposition that prevents shunts, has negligible parasitic absorption, and allows for the sputter deposition of a transparent top electrode. Furthermore, the window layer doubles as a diffusion barrier, increasing the thermal and environmental stability to enable perovskite devices that withstand a 1,000-hour damp heat test at 85 ∘C and 85% relative humidity.
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... However, these silicon cells can be adapted to the particular context of tandem and also undergo special treatment to achieve better performance in this configuration. For example, with an additional layer of MgF 2 or LiF as an anti-reflection coating on the front surface, reflection losses can be reduced to less than 2%, see Fig. 1.10a [66][67][68]. Another optical loss results from the escape of long wavelength photons from the backside (due to back reflection). ...
... This results in periodic nanostructures that are carefully tailored to efficiently trap weakly absorbing infrared photons as shown in Fig. 1.10b [70]. Bush et al. also demonstrated that the SiNP layer on the backside could improve the collection of infrared light [68]. Finally, the bottom silicon cell experiences higher long-wave optical loss (as a percentage of total incident light) than in conventional single-junction cells. ...
... The MAPbI 3 is now replaced by double, triple or even quadruple cation compositions, with at least 2 different halogens. These structures are indeed more stable and have higher UV and heat resistance [68,83,85,86]. Thus all the latest record single-junction perovskite cells since 2016 use a composition with at least two cations, most often MA/FA, see Table A.1 in Appendix A. Nevertheless, there are many other compositions, with now more than 400 different families of perovskites in the photovoltaic field. ...
Thesis
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The current photovoltaic market is dominated by silicon-based solar cells, whose laboratory performance is getting closer and closer to the theoretical limit. To overcome this limit, the most promising approach is the use of a tandem architecture combining a wide bandgap solar cell with a silicon cell. The objective of the thesis is to fabricate a high efficiency, stable and large-size semi-transparent perovskite cell for the realization of a 4-terminal silicon-based tandem cell. The optical losses due to material absorption and reflection at the various interfaces were analyzed in detail by coupling optical modelling and characterization, in order to guide the development of efficient semi-transparent solar cells. In particular, the work focused on replacing the metallic back contact of conventional perovskite cells with a transparent electrode made of ITO, IZO or IO :H, and introducing selective PTAA and SnO₂ contacts. The stacks and processes were optimized to minimize optical and electrical losses, and improve the stability of the devices. Experimental studies on small area perovskite cells and filtered silicon cells have shown a potential efficiency of up to 25%. They also allowed a better understanding of the temporal evolution of the electrical properties, marked by a temporary electrical barrier observed in the first days after the synthesis, and then fading. In addition, the development of an encapsulation process has made it possible to maintain a semi-transparent perovskite cell at more than 90% of its initial efficiency for more than 2 months. Finally, an increase in the size of the devices up to 16 cm² was achieved by the series connection of several cells to form a mini-module with an active surface efficiency of 14.2%, and a perovskite-silicon tandem with the same surface area of 20.8%.
... In recent years, the perovskite material system has gained considerable research attention because of its excellent electronic and optical properties, particularly, its ability to tailor the bandgap and low deposition cost. (Bush et al., 2017a;Chung et al., 2017; Y. C. Kim et al., 2017;M. Liu, Johnston, & Snaith, 2013a Green, Jiang, Soufiani, & Ho-Baillie, 2015;Jang et al., 2016;Jiang, Green, Sheng, & Ho-Baillie, 2015;Li et al., 2015;Shi et al., 2015;L. ...
... of the metal oxide films.4.1.1 Perovskite Solar Cell StructureMost research on PSCs is still focused on single-junction solar cells. However, perovskite and silicon as part of a perovskite/silicon tandem solar cell (TSC) exhibits the largest economic potential, because this combination allows reaching high ECEs, while the manufacturing cost is low.(Bush et al., 2017a;Mohammad I. Hossain et al., 2018a;Jošt et al., 2018;Sahli et al., 2018b;Werner et al., 2018) In this case, the PSC must be integrated on crystalline silicon (c-Si) wafer-based bottom solar cell. Hence, we will focus on device structures in substrate configuration, opposite to solar cells on glass substrates, commonly referred to as solar ...
Thesis
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Metal-halide perovskites are considered as one of the most exciting material systems due to their excellent optoelectronic properties. Notably, the multi-bandgap properties of perovskites have opened an emerging prospect for highly efficient tandem solar cell and color vision applications. So far, only perovskite-based tandem solar cells allow reaching energy conversion efficiencies exceeding 30% at low manufacturing cost. In this thesis, efficient solar cells and color sensors are studied based on metal-halide perovskite materials. Charge transport/contact layers have a significant impact on the electrical and optical properties of perovskite solar cells. Particularly, the front contact, which is a part of the junction of the solar cell, has to be efficient for realizing high energy conversion efficiency. The front contact must provide a lateral charge transport to the terminals and should allow efficient light incoupling while maintaining low optical losses. Hence, In the first part of the thesis, metal-oxides, such as titanium oxide (TiO2), nickel-oxide (NiO), zinc oxide (ZnO), etc., are investigated as potential front contacts for realizing efficient perovskite solar cells. High-quality metal oxide films are prepared by spray pyrolysis deposition (SPD), electron-beam physical vapor deposition (EBPVD), metalorganic chemical vapor deposition (MOCVD), and atomic layer deposition (ALD) techniques. As a first step, the study is carried out to investigate the planar perovskite solar cell performance with different front contacts, which is also used as a reference device structure for future investigations. Subsequently, the study is progressed to the textured perovskite solar cells, which combines the benefit of reaching high shortcircuit current densities and energy conversion efficiencies due to efficient photon management. Efficient photon management allows enhancing photon absorptions in perovskite solar cells through light incoupling and/or light trapping. Herein, light incoupling and light trapping are investigated with the integration of surface textures (e.g. moth-eye, pyramid, optical metasurfaces, etc.) on top of planar perovskite solar cells. A non-resonant optical metasurface is additionally studied as an alternative light-trapping structure for realizing efficient perovskite solar cells, where an array of ZnO nanowires is realized by the templated electrodeposition through a mask of resist. The complex requirements of perovskite solar front contacts and the effect of the front contact on the optics of perovskite solar cells are described in this part of the study. The optics of solar cells is investigated by 3D finite-difference time-domain (FDTD) optical simulations and the electrical effects of solar cells are inspected by the 3D finite element method (FEM). Detailed discussions for the realization of metal oxide films and the influence of photon management on the photovoltaic performance are provided. The second part of this thesis deals with detailed balance calculations and photon management of perovskite-based tandem solar cells. An extended Shockley– Queisser model is used to identify fundamental loss mechanisms and link the losses to the optics of solar cells. The influence of free-carrier absorption of metal oxide films on the optics of low bandgap and/or tandem solar cells is investigated. Herein, an optimized design is proposed for the perovskite/silicon tandem solar cell, which has the potential to reach energy conversion efficiency beyond 30% with a short-circuit current density exceeding 20 mA cm−2 while using realistic device geometry. A hybrid approach is used to investigate the optics of perovskite/silicon tandem solar cells by combining 3D finite-difference time-domain simulations with experimental measurements. Furthermore, multi-bandgap perovskites are employed as absorbers for investigating high-efficiency perovskite/perovskite tandem solar cells at low cost. Details on the nanophotonic design of perovskite-based tandem solar cells are provided. In the final part of this thesis, multi-bandgap perovskite materials are considered for the realization of efficient vertically stacked color sensors. The vertically stacked color sensor consists of three different energy bandgap perovskite diodes (channels), which allows exhibiting excellent color separation without having any color aliasing or color moiré error. The complex material properties of multi-bandgap perovskites are determined by the energy shift modeling. The quantum efficiency of the proposed vertically stacked color sensor is 3 times higher than the conventional filter-based color sensors. The current study focuses on the perovskite color sensor for achieving the quantum efficiency approaching 100%. The quantum efficiency of the investigated sensor is calculated by 3D finite-difference time-domain simulations. The study is further advanced to the realization of the multi-channel color sensor for detecting multispectral imaging, where six individual perovskite diodes are used for the sensor construction. The six-channel sensor outperforms all other characterized sensors. It enables the reconstruction of incident spectra that can be applied to a wide range of areas, such as health, communications, safety, and securities. The colorimetric characterization is performed based on the calculated spectral responsivities of the investigated color sensors. Details on the used materials, the device design, and the colorimetric analysis are provided.
... In the two terminal tandem solar cells, the currents of the two cells must match because they are connected in series [17]. Therefore, the appropriate band gap value of the cell is more limited, with the best value for the bottom cell being 0.94 eV and the best value for the top cell being 1.60 eV [18]. ...
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... Examples of thermo-curable adhesives include ethylene-vinyl acetate (EVA) (Bush et al. 2017), surlyn ionomer , and polyisobutylene (PIB) (Shi et al. 2017 ...
... Examples of thermo-curable adhesives include ethylene-vinyl acetate (EVA) (Bush et al. 2017), surlyn ionomer , and polyisobutylene (PIB) (Shi et al. 2017 ...
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