14 research outputs found
Assessing and Forecasting Atmospheric Outflow of Îą-HCH from China on Intra-, Inter-, and Decadal Time Scales
Atmospheric outflow of Îą-HCH from China from 1952
to 2009
was investigated using Chinese Gridded Pesticide Emission and Residue
Model (ChnGPERM). The model results show that the outflows via the
northeast boundary (NEB, longitude 115â135 °E along 55
°N and latitude 37â55 °N along 135 °E) and the
mid-south boundary (MSB, longitude 100â120 °E along 17
°N) of China account for 47% and 35% of the total outflow, respectively.
Two climate indices based on the statistical association between the
time series of modeled Îą-HCH outflow and atmospheric sea-level
pressure were developed to predict the outflow on different time scales.
The first index explains 70/83% and 10/46% of the intra-annual variability
of the outflow via the NEB and MSB during the periods of 1952â1984
and 1985â2009, respectively. The second index explains 16%
and 19% of the interannual and longer time scale variability in the
outflow through the NEB during JuneâAugust and via the MSB
during OctoberâDecember for 1991â2009, respectively.
Results also revealed that climate warming may potentially result
in stronger outflow via the NEB than the MSB. The linkage between
the outflow with large scale atmospheric circulation patterns and
climate warming trend over China was also discussed
Ternary D1âD2âAâD2 Structured Conjugated Polymer: Efficient âGreenâ Solvent-Processed Polymer/NeatâC<sub>70</sub> Solar Cells
In
contrast to the great efforts on developing novel donor (D)âacceptor
(A) copolymers, research on investigating the backbone composition
of conjugated polymer is rare. In this contribution, we disclose the
design and synthesis of a ternary D1âD2âAâD2
structured conjugated polymer PBSF. Compared to the typical DâA polymer with fixed D/A moiety
number, the ternary structure can tune the optical and electrical
properties more comprehensively and delicately. Precisely control
of the ternary fragments relative to the backbone vector was achieved,
further promoting sufficient planar structure, strong intermolecular
packing, and excellent charge transport. Finally, the additive and
annealing-free polymer solar cells based on PBSF and phenyl-C<sub>71</sub>-butyric acid methyl ester ([70]ÂPCBM; PCE = 7.4%) or cheap,
nonfunctionalized C<sub>70</sub> (PCE = 5.3%) demonstrate excellent
performance using either chlorinated or nonhalogenated âgreenâ
solvent. We believe that this novel and efficient ternary structure
may spark future polymer design to achieve sustainable-processed photovoltaic
devices for practical mass production
Alkenyl Carboxylic Acid: Engineering the Nanomorphology in PolymerâPolymer Solar Cells as Solvent Additive
We have investigated a series of
commercially available alkenyl carboxylic acids with different alkenyl
chain lengths (<i>trans</i>-2-hexenoic acid (CA-6), <i>trans</i>-2-decenoic acid (CA-10), 9-tetradecenoic acid (CA-14))
for use as solvent additives in polymerâpolymer non-fullerene
solar cells. We systematically investigated their effect on the film
absorption, morphology, carrier generation, transport, and recombination
in all-polymer solar cells. We revealed that these additives have
a significant impact on the aggregation of polymer acceptor, leading
to improved phase segregation in the blend film. This in-depth understanding
of the additives effect on the nanomorphology in all-polymer solar
cell can help further boost the device performance. By using CA-10
with the optimal alkenyl chain length, we achieved fine phase separation,
balanced charge transport, and suppressed recombination in all-polymer
solar cells. As a result, an optimal power conversion efficiency (PCE)
of 5.71% was demonstrated which is over 50% higher than that of the
as-cast device (PCE = 3.71%) and slightly higher than that of devices
with DIO treatment (PCE = 5.68%). Compared with widely used DIO, these
halogen-free alkenyl carboxylic acids have a more sustainable processing
as well as better performance, which may make them more promising
candidates for use as processing additives in organic non-fullerene
solar cells
Ultrafast Spectroscopic Identification of Hole Transfer in All-Polymer Blend Films of Poly(1-{4,8-bis[5-(2-ethylhexyl)thiophen-2-yl]-benzo[1,2â<i>b</i>:4,5â<i>b</i>â˛]dithiophen-2-yl}-3-methyl-5-(4-octylphenyl)â4<i>H</i>âthieno[3,4â<i>c</i>]pyrrole-4,6(5<i>H</i>)âdione) and Poly[1,8-bis(dicarboximide)-2,6-diyl]-<i>alt</i>-5,5â˛-(2,2â˛-bithiophene)]
All-polymer
solar cells composed of wide-band-gap polymer polyÂ(1-{4,8-bisÂ[5-(2-ethylhexyl)Âthiophen-2-yl]-benzoÂ[1,2-<i>b</i>:4,5-<i>b</i>â˛]Âdithiophen-2-yl}-3-methyl-5-(4-octylphenyl)-4<i>H</i>-thienoÂ[3,4-<i>c</i>]Âpyrrole-4,6Â(5<i>H</i>)-dione) (PTP8) as the donor and polyÂ[1,8-bisÂ(dicarboximide)-2,6-diyl]-<i>alt</i>-5,5â˛-(2,2â˛-bithiophene)] [PÂ(NDI2OD-T2),
also known as Activink N2200] as the acceptor exhibit a broad absorbance
in the range 300â900 nm, thanks to complementary absorption
of near-infrared light by N2200. Although N2200 shows reasonably high
electron mobility, the contribution of the photogenerated excitons
in N2200 to the power conversion of the PTP8/N2200 solar cell is insignificant.
Here, the hole transfer from N2200 to PTP8 in PTP8/N2200 blend films
was investigated by utilizing ultrafast transient absorption spectroscopy.
The spectral fingerprints of ground-state bleaching and hole polaron-induced
absorption of PTP8 are identified under selective excitation of the
N2200 component and unambiguously indicate hole transfer from N2200
to PTP8. The hole transfer is slow (âź100 ps), comparable to
the geminate exciton recombination rate, consequently limiting the
transfer efficiency and carrier generation. The hole-transfer efficiency
depends on the PTP8/N2200 weight ratio, showing a highest value of
âź14.1% in the 3:2 film
Naphthalene Diimide-Based nâType Polymers: Efficient Rear Interlayers for High-Performance SiliconâOrganic Heterojunction Solar Cells
Siliconâorganic
heterojunction solar cells suffer from a
noticeable weakness of inefficient rear contact. To improve this rear
contact quality, here, two solution-processed organic n-type donorâacceptor
naphthalene diimide (NDI)-based conjugated polymers of N2200 and fluorinated
analogue F-N2200 are explored to reduce the contact resistance as
well as to passivate the Si surface. Both N2200 and F-N2200 exhibit
high electron mobility due to their planar structure and strong intermolecular
stacking, thus allowing them to act as excellent transporting layers.
Preferential orientation of the polymers leads to reduce contact resistance
between Si and cathode aluminum, which can enhance electron extraction.
More importantly, the substitution of fluorine atoms for hydrogen
atoms within the conjugated polymer can strengthen the intermolecular
stacking and improve the polymerâSi electronic contact due
to the existence of F¡¡¡H interactions. The power conversion
efficiencies of Si-PEDOT:PSS solar cells increased from 12.6 to 14.5%
as a consequence of incorporating the F-N2200 polymer interlayers.
Subsequently, in-depth density functional theory simulations confirm
that the polymer orientation plays a critical role on the polymerâSi
contact quality. The success of NDI-based polymers indicates that
planar conjugated polymer with a preferred orientation could be useful
in developing high-performance solution-processed Siâorganic
heterojunction photovoltaic devices
Targeted Design of Surface Configuration on CsPbI<sub>3</sub> Perovskite Nanocrystals for High-Efficiency Photovoltaics
The advanced optoelectronic properties of the emerging
halide perovskite
nanocrystals (PNCs) have brought forth new opportunities for photovoltaic
applications. However, their dynamic ligand binding and fragile crystal
structure make the conventional NC surface manipulation strategies
inaccessible. It is urgent to specially design the surface configuration
of PNCs for high-efficiency photovoltaics. Herein, we develop the
synthesis of CsPbI3 PNCs with a guanidinium (GA)-anchored
surface based on a vacancy-suppressed ternary-precursor method. The
hydrogen bond between GA+ and surrounding iodine can reinforce
the PNC surface and improve surface passivation. Furthermore, the
short GA+ can ensure high interdot coupling in the PNC
film. Therefore, the obtained PNC film can realize both a low trap
density and high carrier mobility. Consequently, a champion power
conversion efficiency (PCE) of 15.83% can be achieved. In addition,
the production yield of our method is significantly higher than that
of the conventional method, which makes the synthesis protocol more
suitable for future scalable manufacturing
Thermal Annealing Effect on Ultrafast Charge Transfer in All-Polymer Solar Cells with a Non-Fullerene Acceptor N2200
Ultrafast transient absorption (TA)
spectroscopy was employed to
investigate the thermal annealing effect on the charge transfer (CT)
in bulk heterojunction (BHJ) all-polymer solar cells (all-PSCs) utilizing
an n-type polymer PÂ(NDI2OD-T2) (Polyera, N2200) as acceptor and a
low bandgap polymer PBPT as donor. The CT generates hole polarons
residing in the PBPT and electron polarons belonging to N2200, manifested
in the TA spectra of the BHJ films as the long-lived absorption peak
centered at âź850 nm. The CT is most efficient in the film annealed
at 160 °C and its efficiency declines monotonically when enhancing
or reducing the annealing temperature, displaying a positive correlation
with the power conversion efficiency (PCE) of the corresponding solar
cell devices. This correlation is analyzed in terms of the crystallinity
and phase separation, which are the key factors determining the performance
of all-PSCs. Our results can provide valuable guidance for the fabrication
of BHJ all-PSCs to improve their PCE
Photovoltaic Performance of Ultrasmall PbSe Quantum Dots
We investigated the effect of PbSe quantum dot size on the performance of Schottky solar cells made in an ITO/PEDOT/PbSe/aluminum structure, varying the PbSe nanoparticle diameter from 1 to 3 nm. In this highly confined regime, we find that the larger particle bandgap can lead to higher open-circuit voltages (âź0.6 V), and thus an increase in overall efficiency compared to previously reported devices of this structure. To carry out this study, we modified existing synthesis methods to obtain ultrasmall PbSe nanocrystals with diameters as small as 1 nm, where the nanocrystal size is controlled by adjusting the growth temperature. As expected, we find that photocurrent decreases with size due to reduced absorption and increased recombination, but we also find that the open-circuit voltage begins to decrease for particles with diameters smaller than 2 nm, most likely due to reduced collection efficiency. Owing to this effect, we find peak performance for devices made with PbSe dots with a first exciton energy of âź1.6 eV (2.3 nm diameter), with a typical efficiency of 3.5%, and a champion device efficiency of 4.57%. Comparing the external quantum efficiency of our devices to an optical model reveals that the photocurrent is also strongly affected by the coherent interference in the thin film due to Fabry-PeĚrot cavity modes within the PbSe layer. Our results demonstrate that even in this simple device architecture, fine-tuning of the nanoparticle size can lead to substantial improvements in efficiency
Inverted Planar Heterojunction Perovskite Solar Cells Employing Polymer as the Electron Conductor
Inverted
planar heterojunction perovskite solar cells employing different polymers,
polyÂ{[<i>N</i>,<i>N</i>â˛-bisÂ(2-octyldodecyl)-1,4,5,8-naphthalene
diimide-2,6-diyl]-<i>alt</i>-5,5â˛-(2,2â˛-bithiophene)}
(N2200), polyÂ{[<i>N</i>,<i>N</i>â˛-bisÂ(alkyl)-1,4,5,8-naphthalene
diimide-2,6-diyl-<i>alt</i>-5,5â˛-diÂ(thiophen-2-yl)-2,2â˛-(E)-2-(2-(thiophen-2-yl)Âvinyl)Âthiophene]}
(PNVT-8), and PNDI2OD-TT as electron-transporting material (ETM) have
been investigated for the first time. The best device performance
was obtained when N2200 was applied as the ETM, with <i>J</i><sub>SC</sub> of 14.70 mA/cm2, <i>V</i><sub>OC</sub> of
0.84 V, and fill factor (FF) of 66%, corresponding to a decent power
conversion efficiency (PCE) of âź8.15%. Which is very competitive
to the parameters (<i>J</i><sub>SC</sub> 14.65 mA/cm2, <i>V</i><sub>OC</sub> 0.83 V, FF 70%, and PCE 8.51%) of the reference
device employing conventional PCBM as the ETM. The slightly lower
FF could be mainly accounted for by the increased recombination in
the polymer contained devices. This work demonstrated that polymeric
materials can be used as efficient ETM in perovskite solar cells,
and we believe this class of polymeric ETMs will further promote the
performance of perovskite photovoltaic cells after extended investigation
Widely Applicable nâType Molecular Doping for Enhanced Photovoltaic Performance of All-Polymer Solar Cells
A widely
applicable doping design for emerging nonfullerene solar cells would
be an efficient strategy in order to further improve device photovoltaic
performance. Herein, a family of compound TBAX (TBA= tetrabutylammonium,
X = F, Cl, Br, or I, containing Lewis base anions are considered as
efficient n-dopants for improving polymerâpolymer solar cells
(all-PSCs) performance. In all cases, significantly increased fill
factor (FF) and slightly increased short-circuit current density (<i>J</i><sub>sc</sub>) are observed, leading to a best PCE of 7.0%
for all-PSCs compared to that of 5.8% in undoped devices. The improvement
may be attributed to interaction between different anions X<sup>â</sup> (X = F, Cl, Br, and I) in TBAX with the polymer acceptor. We reveal
that adding TBAX at relatively low content does not have a significantly
impact on blend morphology, while it can reduce the work function
(WF) of the electron acceptor. We find this simple and solution processable
n-type doping can efficiently restrain charge recombination in all-polymer
solar cell devices, resulting in improved FF and <i>J</i><sub>sc.</sub> More importantly, our findings may provide new protocles
and insights using n-type molecular dopants in improving the performance
of current polymerâpolymer solar cells