Quantum dots crosslinking as a new method for improving charge transport of polymer/quantum dots hybrid solar cells and fabricating solvent-resistant film (original) (raw)
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Applied Physics Letters, 2010
We report on bulk-heterojunction hybrid solar cells based on blends of non-ligand-exchanged CdSe quantum dots ͑QDs͒ and the conjugated polymer poly͑3-hexylthiophene͒ with improved power conversion efficiencies of about 2% under AM1.5G illumination after spectral mismatch correction. This is the highest reported value for a spherical CdSe QD based photovoltaic device. After synthesis, the CdSe QDs are treated by a simple and fast acid-assisted washing procedure, which has been identified as a crucial factor in enhancing the device performance. A simple model of a reduced ligand sphere is proposed explaining the power conversion efficiency improvement.
Solar Energy Materials and Solar Cells, 2011
We report on the efficiency enhancement for bulk-heterojunction hybrid solar cells based on hexanoic acid treated trioctylphosphine/oleic acid-capped CdSe quantum dots (QDs) and low bandgap polymer poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b 0 ]-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) compared to devices based on poly(3-hexylthiophene) (P3HT). Photovoltaic devices with optimized polymer:QD weight ratio, photoactive film thickness, thermal annealing treatment, and cathode materials exhibited a power conversion efficiency of 2.7% after spectral mismatch correction, which is the highest reported value for spherical CdSe QD based photovoltaic devices. The efficiency enhancement is attributed to the surface treatment of the QDs together with the use of the low bandgap polymer PCPDTBT leading to an increased short-circuit current density due to additional light absorption between 650 and 850 nm. Our results suggest that the hexanoic acid treatment is generally applicable to various ligand-capped CdSe and confirm that low bandgap polymers with adequate HOMO and LUMO levels are promising to be incorporated into hybrid solar cells for further device performance improvement.
Macromolecules, 2009
The pending global energy crisis requires the development of new technologies that exploit the potential of renewable sources of energy, such as solar power. For example, inorganic semiconductor-based photovoltaic technology has reached the performance level of converting 30% solar energy into electric power. 1,2 Despite the high performance, inorganic photovoltaics based on crystalline silicon are still too expensive to compete with the conventional sources of electricity. While extensive research in the field of inorganic photovoltaics is expected to result in a decrease in their fabrication cost, polymer-based photovoltaics represent a very attractive alternative for low-cost, lightweight, large-area, and flexible solar panels. The most used conjugated polymers in photovoltaic structures are regioregular poly (3-alkylthiophenes) and alkoxy-substituted poly(phenylenevinylenes), such as poly[2-methoxy-5-(2 0 -ethylhexyloxy)-1,4-phenylenevinylene] and poly[2-methoxy-5-(3 0 ,7 0 -dimethyloctyloxy)-pphenylenevinylene]. 4 Because of their solubility in organic solvents, these polymers are suitable for casting from solution using wet-processing techniques, such as spin-casting, dip-coating, ink jet printing, screen printing, and micromolding. 4 Blending of two materials having donor and acceptor properties results in the formation of a bulk heterojunction. 4 Research has been directed toward four important types of bulk heterojunctions. The first type consists of a polymer-polymer heterojunction obtained by mixing of two conjugated polymers with offset energy levels. The second type is obtained by blending a conjugated polymer with (6,6)-phenyl-C 61 -butyric acid methyl ester (PCBM) as a soluble electron acceptor, which currently shows the best performance. 2,6 Polymer/titania (TiO 2 ) photovoltaic cell represents the third type of bulk heterojunction, which has received attention due to the possibility of TiO 2 patterning into a continuous network for electron transport. 7,8 Conjugated polymer quantum dots can be considered the fourth type of bulk heterojunction solar cells. For example, CdSe nanocrystals with an electron affinity in the range 3.8-4.5 eV are suitable materials to act as electron acceptors when combined with conjugated polymers. 9-12 The band gap for quantum dots is controlled simply by adjusting the size of the dots. Semiconductor quantum dots (QDs) have attracted enormous interest in the past two decades due to their tunable optical and electronic properties. Remarkable efforts have been devoted to the synthesis of high-quality, defect-free QDs with narrow size distribution (<5%). 13 These interesting properties of QDs have been employed for various applications including biosensing, light-emitting diodes, and photovoltaics. Poly(3-alkylthiophenes) are one the most attractive candidates for photovoltaic applications due to their opto-electronic properties, stability, and solution processability. 18 Poly(3-hexylthiophene) (P3HT) has shown hole mobilities as high as 0.1 cm 2 V -1 s -1 and crystallinities as a function of the processing conditions. These are important parameters when considering photovoltaic applications where the effect of charge recombination should be minimized.
Advances in Materials Science and Engineering, 2019
As-synthesized colloidal quantum dots (QDs) are usually covered by an organic capping ligand. These ligands provide colloidal stability by preventing QDs agglomeration. However, their inherent electrical insulation properties deliver a problem for hybrid solar cell application, disrupting charge transfer, and electron transport in conjugated polymer/QDs photoactive blends. Therefore, a surface modification of QDs is crucial before QDs are integrated into solar cell fabrication. In this work, enhancement of power conversion efficiency (PCE) in bulk heterojunction (BHJ) hybrid solar cells based on hexadecylamine- (HDA-) capped CdSe quantum dots (QDs) has been achieved via a postsynthetic hexanoic acid washing treatment. The investigation of the surface modification was performed to find the optimum of washing time and their effect on solar cell devices performance. Variation of washing time between 16 and 30 min has been conducted, and an optimum washing time was found at 22 min, resu...
The Journal of Physical Chemistry C, 2013
Novel quantum dot capping ligands based on fullerene derivatives were attached through click-chemistry to the surface of semiconductor CdSe nanocrystals (C 70 −CdSe). Steady-state and time-correlated luminescence studies in solution show efficient quenching of the quantum dot (QD) emission in C 70 −CdSe. When this material was blended with the polymer poly-3-hexyl thiophene (P3HT) to fabricate bulkheterojunction solar cells, P3HT/C 70 −CdSe devices doubled the light-to-energy conversion efficiency when compared to P3HT/Py−CdSe reference devices prepared using pyridine as the capping agent. This is due to an increase in both photocurrent and fill factor showing the beneficial efficient effect of fullerene to improve light harvesting and charge transport in these devices. However, C 70 also appears to increase recombination in these devices as evidenced by both transient absorption spectroscopy and transient photovoltage measurements. This work also discusses the effects on the CdSe functionalization with C 70 over the device charge recombination kinetics that limit the efficiency in CdSe QDs/polymer solar cells.
Hybrid Solar Cells Based on Blends of CdSe Nanorods and Poly(3-alkylthiophene) Nanofibers
IEEE Journal of Selected Topics in Quantum Electronics, 2000
The influence of the polymer self-organization in poly(3-alkylthiophene):CdSe nanorod (NR) hybrid solar cells is investigated. The solvent used for the spin casting of the hybrid thin films has a strong influence on the device characteristics. Using solar cells of 28-mm 2 active surface, the power conversion efficiency (PCE) was below 0.2% for blends deposited from chloroform, while values of 1.4%-1.6% have been achieved with chlorobenzene (CB) and o-dichlorobenzene (ODCB) under air mass (AM) 1.5 conditions (100 mW/cm 2 ). The slower film growth in the case of the higher boiling point solvents (CB and ODCB) allows the better self-organization of the polymer phase, improving the charge carrier mobility. Subsequently, we report for the first time the use of preformed poly(
Mater. Adv., 2021, 2 (3), 1016-1023, 2021
Hybrid quantum dot solar cell (HQDSC) based on solution-processed blends of poly(3-hexylthiophene) (P3HT) with PbS quantum dots (QDs) is a potential candidate toward practical use for its low material cost and simple fabrication process. However, P3HT is highly incompatible with oleic acid (OA)-capped PbS QDs (OA-PbS QDs) due to strong phase separation, giving poor quality in the desired bi-continuous networks morphology and thus leading to inefficient charge collection. Here, for the first time, a block copolymer of P3HT with polystyrene (P3HT-b-PS) was confirmed to improve the miscibility between the polymers and OA-PbS QDs, leading to the formation of a desirable bi-continuous network morphology, as predicted by us via dissipative dynamic simulations previously. The bi-continuous network morphology for charge transport is an ideal morphology in bulk heterojunction solar cells. For the active layer, using the block copolymer P3HT-b-PS as the donor and PbS QDs as the acceptor at the weight ratio of 1 : 20, the power conversion efficiency (PCE) of HQDSC was found to be 4.18%, which is higher than P3HT and PbS QDs (3.66%) having the same weight ratio even though the content of the P3HT component in P3HT-b-PS was 28% less than that of homo-polymer of P3HT. The formation of the desired morphology for electron and hole collections of the device with the block copolymer was confirmed via scanning electron microscopy. Further, the addition of P3HT into the blend of the block copolymer with OA-PbS QDs still retains the desired morphology. Therefore, further improvement of PCE was made by taking the blend of P3HT and P3HT-b-PS at the weight ratio of 0.7 : 0.3 as the donor, thus achieving the PCE of 4.91%, which is better than that of P3HT alone by 1.25% and P3HT-b-PS alone by 0.73%. Thus, this methodology could be applicable for hybrid solar cells with a low bandgap molecular or polymeric material as the donor.
physica status solidi (a), 2009
The influence of the Cd-to-Se precursor ratio during the synthesis of CdSe nanoparticles (nc-CdSe) on the efficiency of solar cells made from semiconducting polymer/nanocrystalblends (hybrid solar cells) was investigated. In these hybrid solar cells regioregular poly-(3-hexylthiophene 2,5 diyl) (P3HT) was used as the electron donor material while the acceptor was established by CdSe nanocrystals prepared via colloidal synthesis. Furthermore, the influence of the nc-CdSeto-P3HT ratio in the semiconductor blend on the solar cell efficiency was investigated. CdSe:P3HT ratios of 8:1 to 10:1 were found to give the best results concerning the overall device performance as derived from current-voltage characterization. These findings were correlated with structural investigations of the active layer by means of atomic force microscopy (tapping mode AFM). Furthermore, the external quantum efficiency (EQE) of the hybrid solar cells was determined and also used to estimate the short circuit current density J sc under standardized solar irradiation. The J sc values from the EQE measurements were compared to the values obtained from the IV curves. Differences in these values could be explained by an intensitydependent influence of trap states.
Next Generation (Nano) Photonic and Cell Technologies For Solar Energy Conversion Iii, 2012
Semiconductor quantum dots (QDs) are characterized by high extinction coefficients adjustable by varying the nanoparticle size and a high quantum yield of charge generation. They have the advantage of efficient charge transfer from QDs to organic semiconductors. An advanced photovoltaic cell where a SnO 2 /ITO electrode is covered with layers of CdSe QDs integrated in a polyimide (PI) organic semiconductor (about 100 nm thick) and Cu-phthalocyanine (20-40 nm thick) has been developed.