Opportunities for enhancing solar energy harvesting using photon upconversion are reviewed. The increasing prominence of bifacial solar cells is an enabling factor for the implementation of ...upconversion, however, when the realistic constraints of current best-performing silicon devices are considered, many challenges remain before silicon photovoltaics operating under nonconcentrated sunlight can be enhanced via lanthanide-based upconversion. A photophysical model reveals that >1-2 orders of magnitude increase in the intermediate state lifetime, energy transfer rate, or generation rate would be needed before such solar upconversion could start to become efficient. Methods to increase the generation rate such as the use of cosensitizers to expand the absorption range and the use of plasmonics or photonic structures are reviewed. The opportunities and challenges for these approaches (or combinations thereof) to achieve efficient solar upconversion are discussed. The opportunity for enhancing the performance of technologies such as luminescent solar concentrators by combining upconversion together with micro-optics is also reviewed. Triplet-triplet annihilation-based upconversion is progressing steadily toward being relevant to lower-bandgap solar cells. Looking toward photocatalysis, photophysical modeling indicates that current blue-to-ultraviolet lanthanide upconversion systems are very inefficient. However, hope remains in this direction for organic upconversion enhancing the performance of visible-light-active photocatalysts.
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IJS, KILJ, NUK, PNG, UL, UM
The transport of hydrated ions through narrow pores is important for a number of processes such as the desalination and filtration of water and the conductance of ions through biological channels. ...Here, molecular dynamics simulations are used to systematically examine the transport of anionic drinking water contaminants (fluoride, chloride, nitrate, and nitrite) through pores ranging in effective radius from 2.8 to 6.5 Å to elucidate the role of hydration in excluding these species during nanofiltration. Bulk hydration properties (hydrated size and coordination number) are determined for comparison with the situations inside the pores. Free energy profiles for ion transport through the pores show energy barriers depend on pore size, ion type, and membrane surface charge and that the selectivity sequence can change depending on the pore size. Ion coordination numbers along the trajectory showed that partial dehydration of the transported ion is the main contribution to the energy barriers. Ion transport is greatly hindered when the effective pore radius is smaller than the hydrated radius, as the ion has to lose some associated water molecules to enter the pore. Small energy barriers are still observed when pore sizes are larger than the hydrated radius due to re‐orientation of the hydration shell or the loss of more distant water. These results demonstrate the importance of ion dehydration in transport through narrow pores, which increases the current level of mechanistic understanding of membrane‐based desalination and transport in biological channels.
The critical role of ion hydration for determining anion selectivity in narrow pores is examined as a function of anion type, pore size, and surface charge. Ion transport is strongly hindered in narrow pores, due to the energetic expense of the required ion dehydration.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Hybrid organic–inorganic metal halide perovskite semiconductors provide opportunities and challenges for the fabrication of low‐cost thin‐film photovoltaic devices. The opportunities are clear: the ...power conversion efficiency (PCE) of small‐area perovskite photovoltaics has surpassed many established thin‐film technologies. However, the large‐scale solution‐based deposition of perovskite layers introduces challenges. To form perovskite layers, precursor solutions are coated or printed and these must then be crystallized into the perovskite structure. The nucleation and crystal growth must be controlled during film formation and subsequent treatments in order to obtain high‐quality, pin‐hole‐free films over large areas. A great deal of understanding regarding material engineering during the perovskite film formation process has been gained through spin‐coating studies. Based on this, significant progress has been made on transferring material engineering strategies to processes capable of scale‐up, such as blade coating, spray coating, inkjet printing, screen printing, relief printing, and gravure printing. Here, an overview is provided of the strategies that led to devices deposited by these scalable techniques with PCEs as high as 21%. Finally, the opportunities to fully close the shrinking gap to record spin‐coated solar cells and to scale these efficiencies to large areas are highlighted.
Impressive progress has been made in the last few years on producing perovskite photovoltaics using scalable printing and coating technologies. The key developments, such as the control of nucleation and crystal growth of the perovskite thin film, which have enabled this rapid progress in coated and printed perovskite photovoltaics, are highlighted.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
In this work, the authors realize stable and highly efficient wide‐bandgap perovskite solar cells that promise high power conversion efficiencies (PCE) and are likely to play a key role in next ...generation multi‐junction photovoltaics (PV). This work reports on wide‐bandgap (≈1.72 eV) perovskite solar cells exhibiting stable PCEs of up to 19.4% and a remarkably high open‐circuit voltage (VOC) of 1.31 V. The VOC‐to‐bandgap ratio is the highest reported for wide‐bandgap organic−inorganic hybrid perovskite solar cells and the VOC also exceeds 90% of the theoretical maximum, defined by the Shockley–Queisser limit. This advance is based on creating a hybrid 2D/3D perovskite heterostructure. By spin coating n‐butylammonium bromide on the double‐cation perovskite absorber layer, a thin 2D Ruddlesden–Popper perovskite layer of intermediate phases is formed, which mitigates nonradiative recombination in the perovskite absorber layer. As a result, VOC is enhanced by 80 mV.
By coating n‐butylammonium bromide on wide‐bandgap double‐cation perovskite absorber layers (EG ≈ 1.72 eV), a thin 2D Ruddlesden–Popper perovskite layer of intermediate phase is formed. The resulting heterostructure mitigates nonradiative recombination and enables a high open‐circuit voltage of up to 1.31 V and stable power output efficiencies of up to 19.4%.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
This review examines the application of luminescent solar concentrators (LSCs) for building integrated photovoltaics (BIPV), both in terms of opaque façade elements and as semi-transparent windows. ...Many luminophores have been developed for LSC applications, and their efficiencies examined in lab-scale (<25 cm
2
) devices. This analytical review illustrates, using ray-tracing simulations, the technical challenges to maintaining efficiency when scaling these energy conversion devices to pilot- (1000 cm
2
) and commercial-scale (100 000 cm
2
) modules. Based on these considerations, ambitious but feasible target efficiencies for LSCs based on ideal quantum dot (QD) luminophores are suggested as follows - for opaque and semi-transparent (50% average visible transmission), respectively: (i) 11.0% and 5.5% for lab-scale devices; (ii) 10.0% and 5.0% for pilot-scale modules; and (iii) 9.0% and 4.5% for commercial-scale modules. It is worth noting though, that the QD design requirements - particularly with regard to the overlap integral between the absorption and emission spectrum - become very critical as the LSC area increases. Whereas it is difficult to see opaque LSCs successfully competing against standard flat-plate photovoltaic modules for building integration, the application of semi-transparent LSCs as power-generating window elements has potential. Therefore, an economic analysis of the inclusion of LSCs into commercial glazing elements is presented and the potential for novel technologies - such as down-conversion (quantum-cutting) and controlling the direction of emitted light - to move this technology towards application is also discussed.
Semi-transparent luminescent solar concentrators are a promising building integrated photovoltaic technology. But what are the main bottlenecks restricting performance and what stands in the way to commercialisation and market penetration?.
The application of a luminescent down-shifting (LDS) layer has been proposed as a method for improving the poor spectral response (SR) of solar cells to short-wavelength light. The LDS layer absorbs ...photons, typically in the 300–500
nm range, and re-emits them at a longer wavelength where the photovoltaic (PV) device exhibits a significantly better response. This paper reviews the progress in this area over the last three decades, starting from early experiments that yielded promising results but being limited by the luminescent materials available at the time, to modern materials that exhibit higher luminescent quantum efficiencies and better photostability. The candidate materials are considered and their potential is reviewed for a wide range of PV technologies. A particular opportunity is the ability to use the existing polymer encapsulation layer of certain PV technologies as a LDS layer as well.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Sustained stimulated emission under continuous-wave (CW) excitation is a prerequisite for new semiconductor materials being developed for laser gain media. Although hybrid organic-inorganic ...lead-halide perovskites have attracted much attention as optical gain media, the demonstration of room-temperature CW lasing has still not been realized. Here, we present a critical step towards this goal by demonstrating CW amplified spontaneous emission (ASE) in a phase-stable perovskite at temperatures up to 120 K. The phase-stable perovskite maintains its room-temperature phase while undergoing cryogenic cooling and can potentially support CW lasing also at higher temperatures. We find the threshold level for CW ASE to be 387 W cm
at 80 K. These results indicate that easily-fabricated single-phase perovskite thin films can sustain CW stimulated emission, potential at higher temperatures as well, by further optimization of the material quality in order to extend the carrier lifetimes.
Triplet transfer across a surface‐anchored metal–organic‐framework heterojunction is demonstrated by the observation of triplet–triplet annihilation photon upconversion in a sensitizer–emitter ...heterostructure. Upconversion thresholds under 1 mW cm−2 are achieved. In the broader context, the double‐electron‐exchange mechanism of triplet transfer indicates that the heterojunction quality is sufficient for electrons to move between layers in this solution‐processed crystalline heterostructure.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
High‐quality charge carrier transport materials are of key importance for stable and efficient perovskite‐based photovoltaics. This work reports on electron‐beam‐evaporated nickel oxide (NiOx) ...layers, resulting in stable power conversion efficiencies (PCEs) of up to 18.5% when integrated into solar cells employing inkjet‐printed perovskite absorbers. By adding oxygen as a process gas and optimizing the layer thickness, transparent and efficient NiOx hole transport layers (HTLs) are fabricated, exhibiting an average absorptance of only 1%. The versatility of the material is demonstrated for different absorber compositions and deposition techniques. As another highlight of this work, all‐evaporated perovskite solar cells employing an inorganic NiOx HTL are presented, achieving stable PCEs of up to 15.4%. Along with good PCEs, devices with electron‐beam‐evaporated NiOx show improved stability under realistic operating conditions with negligible degradation after 40 h of maximum power point tracking at 75 °C. Additionally, a strong improvement in device stability under ultraviolet radiation is found if compared to conventional perovskite solar cell architectures employing other metal oxide charge transport layers (e.g., titanium dioxide). Finally, an all‐evaporated perovskite solar mini‐module with a NiOx HTL is presented, reaching a PCE of 12.4% on an active device area of 2.3 cm2.
A highly transparent nickel oxide hole transport layer prepared by oxygen‐assisted electron beam evaporation for perovskite‐based photovoltaics is reported. Using these layers in perovskite solar cells, efficient devices with stable power conversion efficiencies up to 18.5% for inkjet‐printed absorbers and 15.4% for co‐evaporated absorbers are demonstrated. In addition, good stability at elevated temperature and under ultraviolet radiation is shown.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
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