as PM6 [13,14] and PBDB-T [15] with narrow bandgap nonfullerene acceptors (A), for example, IT-4F, [14] and Y6 [8] has remained as a wise strategy to absorb solar irradiation in the range of 500-900 nm or even up to a broader absorption region. However, solar irradiation in the spectrum range of 300-500 nm remains unabsorbed. The construction of ternary device by introducing a third component into the photoactive layer has been proven to overcome this issue effectively, where full utilization of solar irradiation in the entire solar spectrum can be realized without complicating the traditional fabrication processes. [16][17][18][19][20][21][22][23] Fullerene derivatives like phenyl-C71-butyric-acid-methyl ester (PC 71 BM) with the main absorption in the range of 300-500 nm have been commonly used as a third component to strengthen the light-harvesting capability of active layers, thus providing a potential route to enhance the short-circuit current density (J sc ) and PCE. [24] Some recent theoretical models and mechanisms have been proposed to provide guide and reference for future development of ternary devices. [25][26][27] Among them, three models which include charge transfer model, [17] energy transfer model, [28] and parallel-like or alloy-like model [16,29] have been widely accepted. In the charge transfer model, the third component in the active layer participates in the process of exciton dissociation and charge carrier generation in the donor/ acceptor interface. [22,30] A cascaded energy level distribution is the requirement for such mechanisms to take place. [31] In contrast, in the energy transfer model, the third component serves as an "energy donor" which absorbs additional solar energy and delivers it to donor or acceptor by Förster or Dexter energy transfer. [32] Ternary devices based on charge transfer or energy transfer mechanisms improve J sc by utilizing additional solar energy. [33,34] Ternary devices based on charge transfer mechanism will affect the open-circuit voltage (V oc ) while the devices based on energy transfer mechanism can hardly impact the V oc due to their roles in charge transfer and dissociation. [35] The third one is the parallel-like or alloy-like model, of which the mechanism does not require any certain energy levels.In parallel-like model, the third component serves as a donor (or acceptor) and work independently with another donor (or acceptor). [36] The ternary device can be viewed as two subcells that are mixed together. For the alloy-like model, the third component is finely mixed with one of the host components to form a two-phase morphology. In this process, dual donors Ternary heterojunction strategies appear to be an efficient approach to improve the efficiency of organic solar cells (OSCs) through harvesting more sunlight. Ternary OSCs are fabricated by employing wide bandgap polymer donor (PM6), narrow bandgap nonfullerene acceptor (Y6), and PC 71 BM as the third component to tune the light absorption and morphologies of the blend films. A record power conver...

With the ZnO/IL interfacial layer, PTB7-Th : PC71BM i-PSCs can exhibit a champion PCE of 10.15%.

Perovskite solar cells as a hot research topic show the necessity of controlling the interface. In this work, an insulating alkyl chain layer is self-assembled at the perovskite/hole transport material interface, which successfully exhibits a dual function: blocking electron recombination and resisting moisture at the same time. Improved solar energy conversion efficiency and stability of the device are both achieved.

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Multiwinner voting rules are used to select a small representative subset of candidates or items from a larger set given the preferences of voters. However, if candidates have sensitive attributes such as gender or ethnicity (when selecting a committee), or specified types such as political leaning (when selecting a subset of news items), an algorithm that chooses a subset by optimizing a multiwinner voting rule may be unbalanced in its selection -it may under or over represent a particular gender or political orientation in the examples above. We introduce an algorithmic framework for multiwinner voting problems when there is an additional requirement that the selected subset should be "fair" with respect to a given set of attributes. Our framework provides the flexibility to (1) specify fairness with respect to multiple, non-disjoint attributes (e.g., ethnicity and gender) and (2) specify a score function. We study the computational complexity of this constrained multiwinner voting problem for monotone and submodular score functions and present several approximation algorithms and matching hardness of approximation results for various attribute group structure and types of score functions. We also present simulations that suggest that adding fairness constraints may not affect the scores significantly when compared to the unconstrained case.

Recently, low temperature solution-processed tin oxide (SnO) as a versatile electron transport layer (ETL) for efficient and robust planar heterojunction (PH) perovskite solar cells (PSCs) has attracted particular attention due to its outstanding properties such as high optical transparency, high electron mobility, and suitable band alignment. However, for most of the reported works, an annealing temperature of 180 °C is generally required. This temperature is reluctantly considered to be a low temperature, especially with respect to the flexible application where 180 °C is still too high for the polyethylene terephthalate flexible substrate to bear. In this contribution, low temperature (about 70 °C) UV/ozone treatment was applied to in situ synthesis of SnO films deposited on the fluorine-doped tin oxide substrate as ETL. This method is a facile photochemical treatment which is simple to operate and can easily eliminate the organic components. Accordingly, PH PSCs with UV-sintered SnO films as ETL were successfully fabricated for the first time. The device exhibited excellent photovoltaic performance as high as 16.21%, which is even higher than the value (11.49%) reported for a counterpart device with solution-processed and high temperature annealed SnO films as ETL. These low temperature solution-processed and UV-sintered SnO films are suitable for the low-cost, large yield solution process on a flexible substrate for optoelectronic devices.

We study the problem of constructing ε-coresets for the (k, z)-clustering problem in a doubling metric M (X, d). An ε-coreset is a weighted subset S ⊆ X with weight function w : S → R ≥0 , such that for any k-subset C ∈ [X] k , it holds thatWe present an efficient algorithm that constructs an ε-coreset for the (k, z)-clustering problem in M (X, d), where the size of the coreset only depends on the parameters k, z, and the doubling dimension ddim(M ). To the best of our knowledge, this is the first efficient -coreset construction of size independent of |X| for general clustering problems in doubling metrics.To this end, we establish the first relation between the doubling dimension of M (X, d) and the shattering dimension (or VC-dimension) of the range space induced by the distance d. Such a relation is not known before, since one can easily construct instances in which neither one can be bounded by (some function of) the other. Surprisingly, we show that if we allow a small (1 ± )-distortion of the distance function d (the distorted distance is called the smoothed distance function), the shattering dimension can be upper bounded by O( −O(ddim(M )) ). For the purpose of coreset construction, the above bound does not suffice as it only works for unweighted spaces. Therefore, we introduce the notion of τ -error probabilistic shattering dimension, and prove a (drastically better) upper bound of O(ddim(M )·log(1/ε)+log log 1 τ ) for the probabilistic shattering dimension for weighted doubling metrics. As it turns out, an upper bound for the probabilistic shattering dimension is enough for constructing a small coreset. We believe the new relation between doubling and shattering dimensions is of independent interest and may find other applications.Furthermore, we study robust coresets for (k, z)-clustering with outliers in a doubling metric. We show an improved connection between α-approximation and robust coresets. This also leads to improvement upon the previous best known bound of the size of robust coreset for Euclidean space [Feldman and Langberg, STOC 11]. The new bound entails a few new results in clustering and property testing.As another application, we show constant-sized (ε, k, z)-centroid sets in doubling metrics can be constructed by extending our coreset construction. Prior to our result, constant-sized centroid sets for general clustering problems were only known for Euclidean spaces. We can apply our centroid set to accelerate the local search algorithm (studied in [Friggstad et al., FOCS 2016]) for the (k, z)-clustering problem in doubling metrics.