SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Fill factor

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A periodically aligned Pt nanocup array is employed as a counter electrode in dye-sensitized solar cells (DSSCs). The Pt nanocup array enhances the catalytic area, which results in a greater fill factor (FF) and higher short-circuit current (J(sc) ). A higher density of nanocups is preferable for the performance of DSSCs.

Concepts: Fill factor, Dye-sensitized solar cell, Photovoltaics, Electrode, Platinum, Solar cell

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A simple solution-processing method was employed to fabricate panchromatic mp-TiO2/CH3NH3PbI3/P3HT-MWNT/Au solar cells. MWNTs in a P3HT-MWNT composite acted as efficient nanostructured charge transport tunnels and induce crystallization of P3HT, hence significantly enhancing the conductivity of the composite. The fill factor of the hybrid solar cells was greatly enhanced by 26.7%.

Concepts: Electric vehicle, Internal combustion engine, Hybrid, P-n junction, Petroleum, Fill factor, Photovoltaics, Solar cell

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Morphology control of solution coated solar cell materials presents a key challenge limiting their device performance and commercial viability. Here we present a new concept for controlling phase separation during solution printing using an all-polymer bulk heterojunction solar cell as a model system. The key aspect of our method lies in the design of fluid flow using a microstructured printing blade, on the basis of the hypothesis of flow-induced polymer crystallization. Our flow design resulted in a ∼90% increase in the donor thin film crystallinity and reduced microphase separated donor and acceptor domain sizes. The improved morphology enhanced all metrics of solar cell device performance across various printing conditions, specifically leading to higher short-circuit current, fill factor, open circuit voltage and significantly reduced device-to-device variation. We expect our design concept to have broad applications beyond all-polymer solar cells because of its simplicity and versatility.

Concepts: P-n junction, Fluid dynamics, IBM, Fill factor, Direct current, Photovoltaics, Solar cells, Solar cell

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Polymer solar cells are a promising technology for the commercialization of low cost, large scale organic solar cells. With the evolution of high efficiency (>13%) non-fullerene polymer solar cells, the stability of the cells has become a crucial parameter to be considered. Among the several degradation mechanisms of polymer solar cells, burn-in photo-degradation is relatively less studied. Herein, we present the first systematic study of photo-degradation of novel PBDB-T:ITIC fullerene-free polymer solar cells. The thermally treated and as-prepared PBDB-T:ITIC solar cells were exposed to continuous 1 sun illumination for 5 hours. The aged devices exhibited rapid losses in the short-circuit current density and fill factor. The severe short-circuit current and fill factor burn in losses were attributed to trap mediated charge recombination, as evidenced by an increase in Urbach energy for aged devices.

Concepts: Sun, Fill factor, Electric current, Electric charge, DNA, Organic solar cell, Photovoltaics, Solar cell

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Employing a layer of bulk-heterojunction (BHJ) organic semiconductors on top of perovskite to further extend its photoresponse is considered as a simple and promising way to enhance the efficiency of perovskite-based solar cells, instead of using tandem devices or near infrared (NIR)-absorbing Sn-containing perovskites. However, the progress made from this approach is quite limited because very few such hybrid solar cells can simultaneously show high short-circuit current (JSC ) and fill factor (FF). To find an appropriate NIR-absorbing BHJ is essential for highly efficient, organic, photovoltaics (OPV)/perovskite hybrid solar cells. The materials involved in the BHJ layer not only need to have broad photoresponse to increase JSC , but also possess suitable energy levels and high mobility to afford high VOC and FF. In this work, a new porphyrin is synthesized and blended with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) to function as an efficient BHJ for OPV/perovskite hybrid solar cells. The extended photoresponse, well-matched energy levels, and high hole mobility from optimized BHJ morphology afford a very high power conversion efficiency (PCE) (19.02%) with high Voc , JSC , and FF achieved simultaneously. This is the highest value reported so far for such hybrid devices, which demonstrates the feasibility of further improving the efficiency of perovskite devices.

Concepts: Methyl acetate, Photovoltaic module, Fill factor, Energy, Energy conversion, Energy conversion efficiency, Photovoltaics, Solar cell

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An all-small-molecule ternary solar cell is achieved with a power conversion efficiency of 10.48% by incorporating phenyl-C71 -butyric-acid-methyl ester (PC71 BM) into a nonfullerene binary system. The addition of PC71 BM is found to modulate the film morphology by improving the domain purity and decreasing the domain size. This modulation facilitates charge generation and suppresses charge recombination, as manifested by the significantly enhanced short-circuit current density and fill factor. The results correlate the domain characteristics with the device performance and offer new insight from the perspective of morphology modulation for constructing efficient ternary devices.

Concepts: Electric current, Fill factor, DNA, Bacteria, Energy conversion, Photovoltaics, Energy conversion efficiency, Solar cell

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Tin-based perovskites have very comparable electronic properties to lead-based perovskites and are regarded as possible lower toxicity alternates for solar cell applications. However, the efficiency of tin-based perovskite solar cells is still low and they exhibit poor air stability. Here, we report lead-free tin-based solar cells with greatly enhanced performance and stability using so-called “hollow” ethylenediammonium and methylammonium tin iodide ({en}MASnI3) perovskite as absorbers. Our results show that en can improve the film morphology and most importantly can serve as a new cation to be incorporated into the 3D MASnI3 lattice. When the cation of en becomes part of the 3D structure, a high density of SnI2 vacancies is created resulting in larger band gap, larger unit cell volume, lower trap-state density, and much longer carrier lifetime compared to classical MASnI3. The best-performing {en}MASnI3 solar cell has achieved a high efficiency of 6.63% with an open circuit voltage of 428.67 mV, a short-circuit current density of 24.28 mA cm-2, and a fill factor of 63.72%. Moreover, the {en}MASnI3 device shows much better air stability than the neat MASnI3 device. Comparable performance is also achieved for cesium tin iodide solar cells with en loading, demonstrating the broad scope of this approach.

Concepts: Photodiode, Direct current, Fill factor, Photovoltaics, Quantum dot, Germanium, Band gap, Solar cell

0

The reduction of charge carrier recombination and intrinsic defect density in organic-inorganic halide perovskite absorber materials is prerequisite to achieving high-performance perovskite solar cells with good efficiency and stability. Here, we fabricated inverted planar perovskite solar cells by incorporation of a small amount of excess organic/inorganic halide (methylammonium iodide (CH3NH3I; MAI), formamidinium iodide (CH(NH2)2I; FAI) and cesium iodide (CsI)) in CH3NH3PbI3 perovskite film. Larger crystalline grains and enhanced crystallinity in CH3NH3PbI3 perovskite films with excess organic/inorganic halide reduce the charge carrier recombination and defect density, leading to enhanced device efficiency (MAI+: 14.49 ± 0.30 %, FAI+: 16.22 ± 0.38 % and CsI+: 17.52 ± 0.56 %) compare to the efficiency of a control MAPbI3 device (MAI: 12.63 ± 0.64 %) and device stability. Especially, the incorporation of a small amount of excess CsI in MAPbI3 perovskite film leads to a highly reproducible fill factor of over 83%, increased open-circuit voltage (from 0.946 V to 1.042 V) and short-circuit current density (from 18.43 mA/cm(2) to 20.89 mA/cm(2)).

Concepts: Electric charge, Fill factor, Carrier generation and recombination, Caesium iodide, Potassium iodide, Caesium, Photovoltaics, Solar cell

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In this work, high-efficiency nonfullerene polymer solar cells (PSCs) are developed based on a thiazolothiazole-containing wide bandgap polymer PTZ1 as donor and a planar IDT-based narrow bandgap small molecule with four side chains (IDIC) as acceptor. Through thermal annealing treatment, a power conversion efficiency (PCE) of up to 11.5% with an open circuit voltage (Voc ) of 0.92 V, a short-circuit current density (Jsc ) of 16.4 mA cm(-2) , and a fill factor of 76.2% is achieved. Furthermore, the PSCs based on PTZ1:IDIC still exhibit a relatively high PCE of 9.6% with the active layer thickness of 210 nm and a superior PCE of 10.5% with the device area of up to 0.81 cm(2) . These results indicate that PTZ1 is a promising polymer donor material for highly efficient fullerene-free PSCs and large-scale devices fabrication.

Concepts: Fill factor, Quantum dot, Photovoltaics, Protein, Band gap, Energy conversion, Energy conversion efficiency, Solar cell

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Trap-assisted recombination, despite being lower as compared with traditional inorganic solar cells, is still the dominant recombination mechanism in perovskite solar cells (PSCs) and limits their efficiency. We investigate the attributes of the primary trap-assisted recombination channels (grain boundaries and interfaces) and their correlation to defect ions in PSCs. We achieve this by using a validated device model to fit the simulations to the experimental data of efficient vacuum-deposited p-i-n and n-i-p CH3NH3PbI3 solar cells, including the light intensity dependence of the open-circuit voltage and fill factor. We find that, despite the presence of traps at interfaces and grain boundaries (GBs), their neutral (when filled with photogenerated charges) disposition along with the long-lived nature of holes leads to the high performance of PSCs. The sign of the traps (when filled) is of little importance in efficient solar cells with compact morphologies (fused GBs, low trap density). On the other hand, solar cells with noncompact morphologies (open GBs, high trap density) are sensitive to the sign of the traps and hence to the cell preparation methods. Even in the presence of traps at GBs, trap-assisted recombination at interfaces (between the transport layers and the perovskite) is the dominant loss mechanism. We find a direct correlation between the density of traps, the density of mobile ionic defects, and the degree of hysteresis observed in the current-voltage (J-V) characteristics. The presence of defect states or mobile ions not only limits the device performance but also plays a role in the J-V hysteresis.

Concepts: Photovoltaics, Ion, Fill factor, DNA, PIN diode, Direct current, Diode, Solar cell