11 research outputs found
Improving Performance of All-Polymer Solar Cells Through Backbone Engineering of Both Donors and Acceptors
All-polymer solar cells (APSCs), composed of semiconducting donor and acceptor polymers, have attracted considerable attention due to their unique advantages compared to polymer-fullerene-based devices in terms of enhanced light absorption and morphological stability. To improve the performance of APSCs, the morphology of the active layer must be optimized. By employing a random copolymerization strategy to control the regularity of the backbone of the donor polymers (PTAZ-TPDx) and acceptor polymers (PNDI-Tx) the morphology can be systematically optimized by tuning the polymer packing and crystallinity. To minimize effects of molecular weight, both donor and acceptor polymers have number-average molecular weights in narrow ranges. Experimental and coarse-grained modeling results disclose that systematic backbone engineering greatly affects the polymer crystallinity and ultimately the phase separation and morphology of the all-polymer blends. Decreasing the backbone regularity of either the donor or the acceptor polymer reduces the local crystallinity of the individual phase in blend films, affording reduced short-circuit current densities and fill factors. This two-dimensional crystallinity optimization strategy locates a PCE maximum at highest crystallinity for both donor and acceptor polymers. Overall, this study demonstrates that proper control of both donor and acceptor polymer crystallinity simultaneously is essential to optimize APSC performance
Aqueous Nanoparticle Polymer Solar Cells: Effects of Surfactant Concentration and Processing on Device Performance
Precise Control of Phase Separation Enables 12% Efficiency in All Small Molecule Solar Cells
Compared to conjugated polymers, small-molecule organic semiconductors present negligible batch-to-batch variations, but presently provide comparatively low power conversion efficiencies (PCEs) in small-molecular organic solar cells (SM-OSCs), mainly due to suboptimal nanomorphology. Achieving precise control of the nanomorphology remains challenging. Here, two new small-molecular donors H13 and H14, created by fluorine and chlorine substitution of the original donor molecule H11, are presented that exhibit a similar or higher degree of crystallinity/aggregation and improved open-circuit voltage with IDIC-4F as acceptor. Due to kinetic and thermodynamic reasons, H13-based blend films possess relatively unfavorable molecular packing and morphology. In contrast, annealed H14-based blends exhibit favorable characteristics, i.e., the highest degree of aggregation with the smallest paracrystalline ÏâÏ distortions and a nanomorphology with relatively pure domains, all of which enable generating and collecting charges more efficiently. As a result, blends with H13 give a similar PCE (10.3%) as those made with H11 (10.4%), while annealed H14-based SM-OSCs have a significantly higher PCE (12.1%). Presently this represents the highest efficiency for SM-OSCs using IDIC-4F as acceptor. The results demonstrate that precise control of phase separation can be achieved by fine-tuning the molecular structure and film formation conditions, improving PCE and providing guidance for morphology design
Precise Control of Phase Separation Enables 12% Efficiency in All Small Molecule Solar Cells
Compared to conjugated polymers, small-molecule organic semiconductors present negligible batch-to-batch variations, but presently provide comparatively low power conversion efficiencies (PCEs) in small-molecular organic solar cells (SM-OSCs), mainly due to suboptimal nanomorphology. Achieving precise control of the nanomorphology remains challenging. Here, two new small-molecular donors H13 and H14, created by fluorine and chlorine substitution of the original donor molecule H11, are presented that exhibit a similar or higher degree of crystallinity/aggregation and improved open-circuit voltage with IDIC-4F as acceptor. Due to kinetic and thermodynamic reasons, H13-based blend films possess relatively unfavorable molecular packing and morphology. In contrast, annealed H14-based blends exhibit favorable characteristics, i.e., the highest degree of aggregation with the smallest paracrystalline ÏâÏ distortions and a nanomorphology with relatively pure domains, all of which enable generating and collecting charges more efficiently. As a result, blends with H13 give a similar PCE (10.3%) as those made with H11 (10.4%), while annealed H14-based SM-OSCs have a significantly higher PCE (12.1%). Presently this represents the highest efficiency for SM-OSCs using IDIC-4F as acceptor. The results demonstrate that precise control of phase separation can be achieved by fine-tuning the molecular structure and film formation conditions, improving PCE and providing guidance for morphology design
The impact of device polarity on the performance of Polymer-Fullerene solar cells
Diketopyrrolopyrrole (DPP)âconjugated polymers are a versatile class of semiconductors for application in organic solar cells because of their tunable optoelectronic properties. A record power conversion efficiency (PCE) of 9.4% was recently achieved for DPP polymers, but further improvements are required to reach true efficiency limits. Using five DPP polymers with different chemical structures and molecular weights, the device performance of polymer:fullerene solar cells is systematically optimized by considering device polarity, morphology, and light absorption. The polymer solubility is found to have a significant effect on the optimal device polarity. Soluble polymers show a 10â25% increase in PCE in inverted device configurations, while the device performance is independent of device polarity for less soluble DPP derivatives. The difference seems related to the polymer to fullerene weight ratio at the ZnO interface in inverted devices, which is higher for more soluble DPP polymers. Optimization of the nature of the cosolvent to narrow the fibril width of polymers in the blends toward the exciton diffusion length enhances charge generation. Additionally, the use of a retroreflective foil increases absorption of light. Combined, the effects afford a PCE of 9.6%, among the highest for DPPâbased polymer solar cells
CCDC 1583669: Experimental Crystal Structure Determination
An entry from the Cambridge Structural Database, the worldâs repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures
âDouble-Cableâ Conjugated Polymers with Linear Backbone toward High Quantum Efficiencies in Single-Component Polymer Solar Cells
A series of âdouble-cableâ
conjugated polymers were
developed for application in efficient single-component polymer solar
cells, in which high quantum efficiencies could be achieved due to
the optimized nanophase separation between donor and acceptor parts.
The new double-cable polymers contain electron-donating polyÂ(benzoÂdithiophene)
(BDT) as linear conjugated backbone for hole transport and pendant
electron-deficient perylene bisimide (PBI) units for electron transport,
connected via a dodecyl linker. Sulfur and fluorine substituents were
introduced to tune the energy levels and crystallinity of the conjugated
polymers. The double-cable polymers adopt a âface-onâ
orientation in which the conjugated BDT backbone and the pendant PBI
units have a preferential ÏâÏ stacking direction
perpendicular to the substrate, favorable for interchain charge transport
normal to the plane. The linear conjugated backbone acts as a scaffold
for the crystallization of the PBI groups, to provide a double-cable
nanophase separation of donor and acceptor phases. The optimized nanophase
separation enables efficient exciton dissociation as well as charge
transport as evidenced from the highîžup to 80%îžinternal
quantum efficiency for photon-to-electron conversion. In single-component
organic solar cells, the double-cable polymers provide power conversion
efficiency up to 4.18%. This is one of the highest performances in
single-component organic solar cells. The nanophase-separated design
can likely be used to achieve high-performance single-component organic
solar cells
Diketopyrrolopyrrole-Based Conjugated Polymers with Perylene Bisimide Side Chains for Single-Component Organic Solar Cells
Diketopyrrolopyrrole-Based Conjugated Polymers with
Perylene Bisimide Side Chains for Single-Component Organic Solar Cell
Effect of Alkyl Side Chains of Conjugated Polymer Donors on the Device Performance of Non-Fullerene Solar Cells
The influence of the chemical structure
of conjugated polymers
on the nanophase separation and device performance in fullerene-based
solar cells has been widely studied, while this is less investigated
in non-fullerene solar cells. In this work, we design three conjugated
polymers with different length of side chains, and we find that the
length of side chains has little influence on the quantum efficiencies
of non-fullerene solar cells. As a comparison, the length of side
chains has a significant effect on the quantum efficiencies of fullerene-based
solar cells. This indicates that morphology of the blended thin films
in non-fullerene solar cells is rather independent of the length of
the donor side chains, and the mechanism for morphology evolution
in the non-fullerene system is completely different from that in the
fullerene system. Our conclusion is confirmed by a variety of advanced
characterization techniques. The studies reveal that in blended thin
films based on the non-fullerene material the donor polymers with
different side chains have a similar coherence length of ÏâÏ
stacking, crystal size and domain purity, giving rise to similar internal
quantum efficiency and power conversion efficiency of the solar cells
Bilayer-Ternary Polymer Solar Cells Fabricated Using Spontaneous Spreading on Water
A new method is presented to fabricate bilayer organic solar cells via sequential deposition of bulkâheterojunction layers obtained using spontaneous spreading of polymerâfullerene blends on a water surface. Using two layers of a small bandgap diketopyrrolopyrrole polymerâfullerene blend, a small improvement in power conversion efficiency (PCE) from 4.9% to 5.1% is obtained compared to spinâcoated devices of similar thickness. Next, bilayerâternary cells are fabricated by first spin coating a wide bandgap thiophene polymerâfullerene blend, followed by depositing a small bandgap diketopyrrolopyrrole polymerâfullerene layer by transfer from a water surface. These novel bilayerâternary devices feature a PCE of 5.9%, higher than that of the individual layers. Remarkable, external quantum efficiencies (EQEs) over 100% are measured for the wide bandgap layer under nearâinfrared bias light illumination. Driftâdiffusion calculations confirm that nearâinfrared bias illumination can result in a significant increase in EQE as a result of a change in the internal electric field in the device, but cannot yet account for the magnitude of the effect. The experimental results indicate that the high EQEs over 100% under bias illumination are related to a barrier for electron transport over the interface between the two blends