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75-468: Nephelium ramboutan-ake , the pulasan , is a tropical fruit in the soapberry family Sapindaceae . It is closely related to the rambutan and sometimes confused with it. Other related soapberry family fruits include lychee and longan . Usually eaten fresh, it is sweeter than the rambutan and lychee, but very rare outside Southeast Asia. The name pulasan comes from the Malay word pulas (twist), related to

150-399: A fill factor of 0.3. An ITO/PPV/Al cell showed an open-circuit voltage of 1 V and a power conversion efficiency of 0.1% under white-light illumination. Single layer organic solar cells do not work well. They have low quantum efficiencies (<1%) and low power conversion efficiencies (<0.1%). A major problem with them is that the electric field resulting from the difference between

225-555: A nectar disc between the petals and stamens, their filaments are often hairy. The most frequent number is eight, in two rings of four. The gynoecium contains two or three carpels , sometimes up to six. The usually single style has a lobed stigma. Most often they are pollinated by birds or insects , with a few species pollinated by wind . Ripe fruits may be fleshy or dry. They may be nuts , berries , drupes , schizocarps , capsules ( Bridgesia ), or samaras ( Acer ). The embryos are bent or coiled, without endosperm in

300-474: A planar heterojunction (Fig. 1). A film of organic active material (polymer or small molecule), of electron donor or electron acceptor type is sandwiched between contacts. Excitons created in the active material may diffuse before recombining and separate, hole and electron diffusing to its specific collecting electrode. Because charge carriers have diffusion lengths of just 3–10 nm in typical amorphous organic semiconductors , planar cells must be thin, but

375-577: A " geminate pair ", and an electric field is then required to separate them. The electron and hole must be collected at contacts. If charge carrier mobility is insufficient, the carriers will not reach the contacts, and instead recombine at trap sites or remain in the device as undesirable space charges that oppose the flow of new carriers. The latter problem can occur if electron and hole mobilities are not matched. In that case, space-charge limited photocurrent (SCLP) hampers device performance. Organic photovoltaics can be fabricated with an active polymer and

450-460: A cell with a fill factor as high as 0.65 and a power conversion efficiency of 1% under simulated AM2 illumination. Halls et al. fabricated a cell with a layer of bis(phenethylimido) perylene over a layer of PPV as the electron donor. This cell had peak external quantum efficiency of 6% and power conversion efficiency of 1% under monochromatic illumination, and a fill factor of up to 0.6. The diffusion length of excitons in organic electronic materials

525-433: A conversion efficiency of 8.4%. The implementation produced high open-circuit voltages and absorption in the visible spectra and high short-circuit currents. Quantum efficiency was above 75% between 400 nm and 720 nm wavelengths, with an open-circuit voltage around 1 V. Bulk heterojunctions have an absorption layer consisting of a nanoscale blend of donor and acceptor materials. The domain sizes of this blend are on

600-409: A fullerene-based electron acceptor. Illumination of this system by visible light leads to electron transfer from the polymer to a fullerene molecule. As a result, the formation of a photoinduced quasiparticle , or polaron (P ), occurs on the polymer chain and the fullerene becomes a radical anion ( C 60 ). Polarons are highly mobile and can diffuse away. In organic solar cells, junctions are

675-529: A good acceptor. A C 60 /MEH-PPV double layer cell had a relatively high fill factor of 0.48 and a power conversion efficiency of 0.04% under monochromatic illumination. PPV/C 60 cells displayed a monochromatic external quantum efficiency of 9%, a power conversion efficiency of 1% and a fill factor of 0.48. Perylene derivatives display high electron affinity and chemical stability. A layer of copper phthalocyanine (CuPc) as electron donor and perylene tetracarboxylic derivative as electron acceptor, fabricating

750-547: A heterojunction between two dissimilar materials. In organic photovoltaics, effective fields break up excitons by causing the electron to fall from the conduction band of the absorber to the conduction band of the acceptor molecule. It is necessary that the acceptor material has a conduction band edge that is lower than that of the absorber material. Polymer solar cells usually consist of an electron- or hole-blocking layer on top of an indium tin oxide (ITO) conductive glass followed by electron donor and an electron acceptor (in

825-542: A layer of low work function metal such as Aluminum, Magnesium or Calcium. The basic structure of such a cell is illustrated in Fig. 5. The difference of work function between the two conductors sets up an electric field in the organic layer. When the organic layer absorbs light, electrons will be excited to the LUMO and leave holes in the HOMO, thereby forming excitons . The potential created by

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900-499: A photovoltage of 200 mV. An Al/MgPc/Ag cell obtained photovoltaic efficiency of 0.01% under illumination at 690 nm. Conjugated polymers were also used in this type of photovoltaic cell. One device used polyacetylene (Fig. 1) as the organic layer, with Al and graphite , producing an open-circuit voltage of 0.3 V and a charge collection efficiency of 0.3%. An Al/poly(3-nethyl-thiophene)/Pt cell had an external quantum yield of 0.17%, an open-circuit voltage of 0.4 V and

975-514: A power conversion efficiency of 10.61% with a blend of PC 71 BM as the electron acceptor and PTB7-Th as the electron donor. Polymer/polymer blends are also used in dispersed heterojunction photovoltaic cells. A blend of CN-PPV and MEH-PPV with Al and ITO as the electrodes, yielded peak monochromatic power conversion efficiency of 1% and fill factor of 0.38. Dye sensitized photovoltaic cells can also be considered important examples of this type. Issues Fullerenes such as PC 71 BM are often

1050-437: A secondary p-type donor polymer, acts to absorb light in a different region of the solar spectrum. This in theory increases the amount of absorbed light. These ternary cells operate through one of three distinct mechanisms: charge transfer, energy transfer or parallel-linkage. In charge transfer, both donors contribute directly to the generation of free charge carriers. Holes pass through only one donor domain before collection at

1125-683: A slower rate (as chlorobenzene (CB) or dichlorobenzene (DCB)) you can get larger degrees of vertical separation or aggregation while solvents that evaporate quicker produce a much less effective vertical separation. Larger solubility gradients should lead to more effective vertical separation while smaller gradients should lead to more homogeneous films. These two effects were verified on P3HT:PCBM solar cells. The solvent evaporation speed as well as posterior solvent vapor or thermal annealing procedures were also studied. Blends such as P3HT:PCBM seem to benefit from thermal annealing procedures, while others, such as PTB7:PCBM, seem to show no benefit. In P3HT

1200-478: A solution containing the two components, casting ( e.g., drop casting and spin coating ) and then allowing the two phases to separate, usually with the assistance of an annealing step. The two components will self-assemble into an interpenetrating network connecting the two electrodes. They are normally composed of a conjugated molecule based donor and fullerene based acceptor. The nanostructural morphology of bulk heterojunctions tends to be difficult to control, but

1275-421: A way that the gradient is gradual. This architecture combines the short electron travel distance in the dispersed heterojunction with the advantage of the charge gradient of the bilayer technology. A cell with a blend of CuPc and C 60 showed a quantum efficiency of 50% and a power conversion efficiency of 2.1% using 100 mW/cm simulated AM1.5G solar illumination for a graded heterojunction. Similar to

1350-469: A π -π* transition. The energy bandgap between these orbitals determines which wavelength(s) of light can be absorbed . Unlike in an inorganic crystalline PV cell material, with its band structure and delocalized electrons, excitons in organic photovoltaics are strongly bound with an energy between 0.1 and 1.4 eV . This strong binding occurs because electronic wave functions in organic molecules are more localized, and electrostatic attraction can thus keep

1425-494: Is critical to photovoltaic performance. After the capture of a photon, electrons move to the acceptor domains, then are carried through the device and collected by one electrode, and holes move in the opposite direction and collected at the other side. If the dispersion of the two materials is too fine, it will result in poor charge transfer through the layer. Most bulk heterojunction cells use two components, although three-component cells have been explored. The third component,

1500-452: Is divided into four subfamilies, Dodonaeoideae (about 38 genera), Sapindoideae (about 114 genera), Hippocastanoideae (5 genera) and Xanthoceroideae (1 genus). The largest genera are Serjania (about 220 species), Paullinia (about 180 species), and Allophylus (about 200 species) in the tropical Sapindoideae and Acer (about 110 species) in the temperate Hippocastanoideae. The largely temperate genera formerly separated in

1575-498: Is important for small autonomous sensors), potentially disposable and inexpensive to fabricate (sometimes using printed electronics ), flexible, customizable on the molecular level and potentially have less adverse environmental impact. Polymer solar cells also have the potential to exhibit transparency, suggesting applications in windows, walls, flexible electronics, etc. An example device is shown in Fig. 1. The disadvantages of polymer solar cells are also serious: they offer about 1/3 of

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1650-653: Is little known elsewhere in the New World except in Costa Rica where it is occasionally grown and the fruits sometimes appear on the market. Like its relatives, pulasan can be propagated by seed and grafting methods. Grafting is a common practice among horticulturalists that often is a proactive method of preventing disease, by using healthy rootstocks. Though starting by seed can be successful, most producers will not use this method of propagation due to variation in gender, which causes chance in having an actual fruiting tree. Of

1725-446: Is more soluble in the solvent than the other, it will deposit first on top of the substrate , causing a concentration gradient through the film. This has been demonstrated for poly-3-hexyl thiophene (P3HT), phenyl-C 61 -butyric acid methyl ester ( PCBM ) devices where the PCBM tends to accumulate towards the device's bottom upon spin coating from ODCB solutions. This effect is seen because

1800-446: Is said that the tree bears best after a long, dry season . The fruit is ovoid , 5-7.5 cm long, dark red, with its thick, leathery rind closely set with conical, blunt-tipped tubercles or thick, fleshy, straight spines, which are up to 1 cm long. There may be one or two small, undeveloped fruits nestled close to the stem. Within is the glistening, white or yellowish-white flesh (aril) to 1 cm thick, more or less clinging to

1875-560: Is the source of Indian macassar oil . Saponins extracted from the drupe of Sapindus species are effective surfactants and are used commercially in cosmetics and detergents . Organic solar cell The molecules used in organic solar cells are solution-processable at high throughput and are cheap, resulting in low production costs to fabricate a large volume. Combined with the flexibility of organic molecules , organic solar cells are potentially cost-effective for photovoltaic applications. Molecular engineering ( e.g., changing

1950-486: Is typically on the order of 10 nm. In order for most excitons to diffuse to the interface of layers and split into carriers, the layer thickness should be in the same range as the diffusion length. However, a polymer layer typically needs a thickness of at least 100 nm to absorb enough light. At such a large thickness, only a small fraction of the excitons can reach the heterojunction interface. A three-layer (two acceptor and one donor) fullerene -free stack achieved

2025-649: The Visayan pulas (take off, remove) and Tagalog pilas (rip, tear). The fruit is opened through the act of twisting the fruit with both hands, thus the name pulasan . The pulasan tree is an ornamental . It attains a height of 10–15 m and has a short trunk to 30–40 cm thick. The branchlets are brown and hairy when young. The alternate leaves, pinnate or odd-pinnate, are 17–45 cm long, have 2 to 5 pairs of opposite or nearly opposite leaflets, are oblong or elliptic-lanceolate, 6.25-17.5 cm long and up to 5 cm wide; slightly wavy, dark-green and barely glossy on

2100-879: The Malay Peninsula and Thailand ; is rarely domesticated in the Philippines. Ochse reported that there were extensive plantings in Java only around Bogor and the villages along the railway between Bogor and the capital Jakarta . The tree was planted at the Trujillo Plant Propagation Station in Puerto Rico in 1926 and young trees from Java were sent to the Lancetilla Experimental Garden, Tela, Honduras , in 1927. The latter were said in 1945 to be doing well at Tela and fruiting moderately. The pulasan

2175-488: The PCBM and the cathode is required for better efficiencies, this largely increases device reproducibility. According to neutron scattering analysis, P3HT:PCBM blends have been described as "rivers" (P3HT regions) interrupted by "streams" (PCBM regions). Mostly organic films for photovoltaic applications are deposited by spin coating and vapor-phase deposition. However each method has certain draw backs, spin coating technique can coat larger surface areas with high speed but

2250-425: The absence of pure amorphous regions. Since current models assume phase separation at interfaces without any consideration for phase purity, the models might need to be changed. The thermal annealing procedure varies depending on precisely when it is applied. Since vertical species migration is partly determined by the surface tension between the active layer and either air or another layer, annealing before or after

2325-479: The anode. In energy transfer, only one donor contributes to the production of holes. The second donor acts solely to absorb light, transferring extra energy to the first donor material. In parallel linkage, both donors produce excitons independently, which then migrate to their respective donor/acceptor interfaces and dissociate. Fullerenes such as C 60 and its derivatives are used as electron acceptor materials in bulk heterojunction photovoltaic cells. A cell with

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2400-681: The benefit seems to come from an increase of crystallinity of the P3HT phase which is generated through an expulsion of PCBM molecules from within these domains. This has been demonstrated through studies of PCBM miscibility in P3HT as well as domain composition changes as a function of annealing times. The above hypothesis based on miscibility does not fully explain the efficiency of the devices as solely pure amorphous phases of either donor or acceptor materials never exist within bulk heterojunction devices. A 2010 paper suggested that current models that assume pure phases and discrete interfaces might fail given

2475-410: The blend of MEH-PPV and a methano-functionalized C 60 derivative as the heterojunction, ITO and Ca as the electrodes showed a quantum efficiency of 29% and a power conversion efficiency of 2.9% under monochromatic illumination. Replacing MEH-PPV with P3HT produced a quantum yield of 45% under a 10 V reverse bias. Further advances in modifying the electron acceptor has resulted in a device with

2550-399: The case of bulk heterojunction solar cells), a hole or electron blocking layer, and metal electrode on top. The nature and order of the blocking layers – as well as the nature of the metal electrode – depends on whether the cell follows a regular or an inverted device architecture. In an inverted cell, the electric charges exit the device in the opposite direction as in a normal device because

2625-403: The chamber can contaminate later depositions. This "line of sight" technique also can create holes in the film due to shadowing, which causes an increase in the device series-resistance and short circuit. Organic vapor phase deposition (OVPD), shown in Fig. 9(b), allows better control of the structure and morphology of the film than vacuum thermal evaporation. The process involves evaporation of

2700-419: The deposition of additional layers (most often the metal cathode) affects the result. In the case of P3HT:PCBM solar cells vertical migration is improved when cells are annealed after the deposition of the metal cathode. Donor or acceptor accumulation next to the adjacent layers might be beneficial as these accumulations can lead to hole or electron blocking effects which might benefit device performance. In 2009

2775-499: The device's active layer. These charges then transport to the device's electrodes where the charges flow outside the cell, perform work and then re-enter the device on the opposite side. The cell's efficiency is limited by several factors, especially non-geminate recombination . Hole mobility leads to faster conduction across the active layer. Organic photovoltaics are made of electron donor and electron acceptor materials rather than semiconductor p-n junctions . The molecules forming

2850-417: The difference in vertical distribution on P3HT:PCBM solar cells was shown to cause problems with electron mobility which ends up with the yielding of very poor device efficiencies. Simple changes to device architecture – spin coating a thin layer of PCBM on top of the P3HT – greatly enhance cell reproducibility, by providing reproducible vertical separation between device components. Since higher contact between

2925-415: The differences large enough that these local electric fields are strong, which splits excitons much more efficiently than single layer photovoltaic cells. The layer with higher electron affinity and ionization potential is the electron acceptor, and the other layer is the electron donor. This structure is also called a planar donor-acceptor heterojunction . C 60 has high electron affinity, making it

3000-458: The different work functions helps to split the exciton pairs, pulling electrons to the positive electrode (an electrical conductor used to make contact with a non-metallic part of a circuit) and holes to the negative electrode. In 1958 the photovoltaic effect or the creation of voltage of a cell based on magnesium phthalocyanine (MgPc)—a macrocyclic compound having an alternating nitrogen atom-carbon atom ring structure—was discovered to have

3075-416: The donor-acceptor weight ratio. The next logical step beyond BHJs are ordered nanomaterials for solar cells, or ordered heterojunctions (OHJs). OHJs minimize the variability associated with BHJs. OHJs are generally hybrids of ordered inorganic materials and organic active regions. For example, a photovoltaic polymer can be deposited into pores in a ceramic such as TiO 2 . Since holes still must diffuse

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3150-422: The efficiency of hard materials, and experience substantial photochemical degradation. Polymer solar cells' stability problems, combined with their promise of low costs and potential for increasing efficiencies have made them a popular field in solar cell research. In 2015, polymer solar cells were achieving efficiencies of more than 10% via a tandem structure. In 2023, a new record-breaking efficiency of 19.3%

3225-664: The electron acceptor materials found in high performing bulk heterojunction solar cells. However, these electron acceptor materials very weakly absorb visible light, decreasing the volume fraction occupied by the strongly absorbing electron donor material. Furthermore, fullerenes have poor electronic tunability, resulting in restrictions placed on the development of conjugated systems with more appealing electronic structures for higher voltages. Recent research has been done on trying to replace these fullerenes with organic molecules that can be electronically tuned and contribute to light absorption. The electron donor and acceptor are mixed in such

3300-436: The electron and hole together as an exciton. The electron and hole can be dissociated by providing an interface across which the chemical potential of electrons decreases. The material that absorbs the photon is the donor, and the material acquiring the electron is called the acceptor. In Fig. 3, the polymer chain is the donor and the fullerene is the acceptor. Even after dissociation, the electron and hole may still be joined as

3375-433: The electron donor region of organic PV cells, where exciton electron-hole pairs are generated, are generally conjugated polymers possessing delocalized π electrons that result from carbon p orbital hybridization. These π electrons can be excited by light in or near the visible part of the spectrum from the molecule's highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO), denoted by

3450-498: The electron transporting electrode (Electrode 2). Without this percolating network, charges might be trapped in a donor or acceptor rich domain and undergo recombination. Bulk heterojunctions have an advantage over layered photoactive structures because they can be made thick enough for effective photon absorption without the difficult processing involved in orienting a layered structure while retaining similar level of performances. Bulk heterojunctions are most commonly created by forming

3525-894: The families Aceraceae ( Acer , Dipteronia ) and Hippocastanaceae ( Aesculus , Billia , Handeliodendron ) were included within a more broadly circumscribed Sapindaceae by the Angiosperm Phylogeny Group . Recent research has confirmed the inclusion of these genera in the Sapindaceae. The Sapindaceae include many species of economically valuable tropical fruit , including the lychee , longan , pitomba , guinip/mamoncillo , korlan , rambutan , pulasan , and ackee . Other products include guaraná , soapberries , and maple syrup . Some species of maple and buckeye are valued for their wood, while several other genera, such as Koelreuteria , Cardiospermum , and Ungnadia , are popular ornamentals . Schleichera trijuga

3600-435: The flakes coming out of the walls of the chamber, as the walls are warm and do not allow molecules to stick to and produce a film upon them. Another advantage over VTE is the uniformity in evaporation rate. This occurs because the carrier gas becomes saturated with the vapors of the organic material coming out of the source and then moves towards the cooled substrate, Fig. 9(b). Depending on the growth parameters (temperature of

3675-400: The graded heterojunction the continuous junction concept aims at realizing a gradual transition from an electron donor to an electron acceptor. However, the acceptor material is prepared directly from the donor polymer in a post-polymerization modification step. Since its active layer largely determines device efficiency, this component's morphology received much attention. If one material

3750-424: The hole-collecting electrode can only be achieved for relatively thin (100 nm) P3HT/PCBM layers. The gradients in the initial morphology are then mainly generated by the solvent evaporation rate and the differences in solubility between the donor and acceptor inside the blend. This dependence on solubility has been clearly demonstrated using fullerene derivatives and P3HT. When using solvents which evaporate at

3825-405: The interfaces between different layers or materials within the device's structure. These interfaces contribute to the separation and collection of charge carriers (electrons and holes) that are generated when sunlight is absorbed. The properties and structures of these junctions affects the efficiency, stability, and overall performance of organic solar cells. The simplest organic PV device features

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3900-576: The length and functional group of polymers ) can change the band gap , allowing for electronic tunability. The optical absorption coefficient of organic molecules is high, so a large amount of light can be absorbed with a small amount of materials, usually on the order of hundreds of nanometers. The main disadvantages associated with organic photovoltaic cells are low efficiency , low stability and low strength compared to inorganic photovoltaic cells such as silicon solar cells . Compared to silicon -based devices, polymer solar cells are lightweight (which

3975-446: The length of the pore through the polymer to a contact, OHJs suffer similar thickness limitations. Mitigating the hole mobility bottleneck is key to further enhancing device performance of OHJ's. Single layer organic photovoltaic cells are the simplest form. These cells are made by sandwiching a layer of organic electronic materials between two metallic conductors, typically a layer of indium tin oxide (ITO) with high work function and

4050-421: The light-absorbing material in photovoltaics is that they all have large conjugated systems . A conjugated system is formed where carbon atoms covalently bond with alternating single and double bonds. These hydrocarbons' electrons pz orbitals delocalize and form a delocalized bonding π orbital with a π* antibonding orbital. The delocalized π orbital is the highest occupied molecular orbital ( HOMO ), and

4125-643: The material can be absorbed, though there is a trade-off to reducing the band gap as photons absorbed with energies higher than the band gap will thermally give off their excess energy, resulting in lower voltages and power conversion efficiencies. When these materials absorb a photon , an excited state is created and confined to a molecule or a region of a polymer chain. The excited state can be regarded as an exciton , or an electron-hole pair bound together by electrostatic interactions. In photovoltaic cells, excitons are broken up into free electron-hole pairs by effective fields. The effective fields are set up by creating

4200-481: The more soluble component tends to migrate towards the "solvent rich" phase during the coating procedure, accumulating the more soluble component towards the film's bottom, where the solvent remains longer. The thickness of the generated film affects the phases segregation because the dynamics of crystallization and precipitation are different for more concentrated solutions or faster evaporation rates (needed to build thicker devices). Crystalline P3HT enrichment closer to

4275-401: The order of nanometers, allowing for excitons with short lifetimes to reach an interface and dissociate due to the large donor-acceptor interfacial area. However, efficient bulk heterojunctions need to maintain large enough domain sizes to form a percolating network that allows the donor materials to reach the hole transporting electrode (Electrode 1 in Fig. 7) and the acceptor materials to reach

4350-435: The organic material over a substrate in the presence of an inert carrier gas. The resulting film morphology can be tuned by changing the gas flow rate and the source temperature. Uniform films can be grown by reducing the carrier gas pressure, which will increase the velocity and mean free path of the gas, and as a result boundary layer thickness decreases. Cells produced by OVPD do not have issues related with contaminations from

4425-446: The positive and negative electrodes are reversed. Inverted cells can utilize cathodes out of a more suitable material; inverted OPVs enjoy longer lifetimes than regularly structured OPVs, and they usually show higher efficiencies compared with the conventional counterparts. In bulk heterojunction polymer solar cells, light generates excitons. Subsequent charge separation in the interface between an electron donor and acceptor blend within

4500-413: The pulasan flower parts, the anther cannot open on its own; this means that the plant cannot pollinate itself. Certain trees will have hermaphrodite flowers, and others will have staminate flowers. Generally this means hermaphrodites will take on female roles as the staminates take male, in the pollination process. Pulasan skin is unique for its color; it offers a natural dye, one that has recently been

4575-427: The rambutan. In addition, unlike the seed of the rambutan, the seed of the pulasan is readily edible raw. It has a flavor somewhat like that of almonds. The pulasan is native to Malay Peninsula and other parts of tropical Southeast Asia. Wild trees are infrequent in lowland forests around Perak , Malaysia but abundant in the Philippines at low elevations from Luzon to Mindanao . The tree has long been cultivated in

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4650-624: The seed, and frequently with an aril . The Sapindaceae are related to the Rutaceae , and both are usually placed in an order Sapindales or Rutales , depending on whether they are kept separate and which name is used for the order. The most basal member appears to be Xanthoceras . Some authors formerly maintained some or all of Hippocastanaceae and Aceraceae , however this resulted in paraphyly . The former Ptaeroxylaceae , now placed in Rutaceae, were sometimes placed in Sapindaceae. The family

4725-405: The source so that evaporated material may be directly deposited onto the substrate, as shown in Fig. 9(a). This method is useful for depositing many layers of different materials without chemical interaction between different layers. However, there are sometimes problems with film-thickness uniformity and uniform doping over large-area substrates. In addition, the materials that deposit on the wall of

4800-792: The source, base pressure and flux of the carrier gas) the deposited film can be crystalline or amorphous in nature. Devices fabricated using OVPD show a higher short-circuit current density than that of devices made using VTE. An extra layer of donor-acceptor hetero-junction at the top of the cell may block excitons, whilst allowing conduction of electron; resulting in improved cell efficiency. Conditions for spin coating and evaporation affect device efficiency. Solvent and additives influence donor-acceptor morphology. Additives slow down evaporation, leading to more crystalline polymers and thus improved hole conductivities and efficiencies. Typical additives include 1,8-octanedithiol, ortho-dichlorobenzene , 1,8-diiodooctane (DIO), and nitrobenzene . The DIO effect

4875-472: The specimen of studies dealing with electrical conductivity and its potential in renewable energy (see OSC 's). Sapindaceae The Sapindaceae are a family of flowering plants in the order Sapindales known as the soapberry family . It contains 138 genera and 1,858 accepted species. Examples include horse chestnut , maples , ackee and lychee . The Sapindaceae occur in temperate to tropical regions, many in laurel forest habitat, throughout

4950-805: The temperate maples ( Acer ), Aesculus , and a few other genera are opposite. They are most often pinnately compound , but are palmately compound in Aesculus , and simply palmate in Acer . The petiole has a swollen base and lacks stipules . Some genera and species have laurel forest foliage due to convergent evolution . The flowers are small and unisexual , or functionally unisexual, though plants may be either dioecious or monoecious. They are usually found in cymes grouped in panicles . They most often have four or five petals and sepals (petals are absent in Dodonaea ). The stamens range from four to 10, usually on

5025-450: The thin cells absorb light less well. Bulk heterojunctions (BHJs) address this shortcoming. In a BHJ, a blend of electron donor and acceptor materials is cast as a mixture, which then phase-separates. Regions of each material in the device are separated by only several nanometers, a distance suited for carrier diffusion. BHJs require sensitive control over materials morphology on the nanoscale. Important variables include materials, solvents and

5100-402: The thin, grayish-brown seedcoat (testa) which separates from the seed. The flavor is generally much sweeter than that of the rambutan . The seed is ovoid, oblong or ellipsoid, light brown, somewhat flattened on one side, and 2 to 3.5 cm long. While similar to rambutan, the fruit lacks the hairy spines. The flesh is sweet and juicy, and separates easily from the seed, much more easily than

5175-535: The two conductive electrodes is seldom sufficient to split the excitons. Often the electrons recombine with the holes without reaching the electrode. Bilayer cells contain two layers in between the conductive electrodes (Fig. 6). The two layers have different electron affinity and ionization energies , therefore electrostatic forces are generated at the interface between the two layers. Light must create excitons in this small charged region for an efficient charge separation and collecting. The materials are chosen to make

5250-436: The upper surface; pale, and somewhat bluish, with a few short, silky hairs on the underside. Very small, greenish, petalless flowers with 4-5 hairy sepals are borne singly or in clusters on the branches of the erect, axillary or terminal, panicles clothed with fine yellowish or brownish hairs. The pulasan is ultra-tropical and thrives only in humid regions between 360 and 1,150 ft (110–350 m) of altitude. In Malaysia, it

5325-419: The use of solvent for one layer can degrade the already existing polymer layer. Another problem is related with the patterning of the substrate for device as spin-coating results in coating the entire substrate with a single material. Another deposition technique is vacuum thermal evaporation (VTE) which involves the heating of an organic material in vacuum. The substrate is placed several centimeters away from

5400-459: The world. Many are laticiferous , i.e. they contain latex , a milky sap , and many contain mildly toxic saponins with soap -like qualities in either the foliage and/or the seeds, or roots. The largest genera are Serjania , Paullinia , Allophylus and Acer . Plants of this family have a variety of habits, from trees to herbaceous plants to lianas . The leaves of the tropical genera are usually spirally alternate, while those of

5475-413: The π* orbital is the lowest unoccupied molecular orbital ( LUMO ). In organic semiconductor physics, the HOMO takes the role of the valence band while the LUMO serves as the conduction band . The energy separation between the HOMO and LUMO energy levels is considered the band gap of organic electronic materials and is typically in the range of 1–4 eV . All light with energy greater than the band gap of

5550-446: Was achieved by Hong Kong Polytechnic University . A photovoltaic cell is a specialized semiconductor diode that converts light into direct current (DC) electricity. Depending on the band gap of the light-absorbing material, photovoltaic cells can also convert low-energy, infrared (IR) or high-energy, ultraviolet (UV) photons into DC electricity. A common characteristic of both the small molecules and polymers (Fig. 3) used as

5625-478: Was attributed to the selective solubilization of PCBM components, modifies fundamentally the average hopping distance of electrons, and thus improves electron mobility. Additives can also lead to big increases in efficiency for polymers. For HXS-1/PCBM solar cells, the effect was correlated with charge generation, transport and shelf-stability. Other polymers such as PTTBO also benefit significantly from DIO, achieving PCE values of more than 5% from around 3.7% without

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