Hybrid Bulk Heterojunction Solar Cells Research Articles

Influences of CdSe NCs on the photovoltaic parameters of BHJ organic solar cells

In this study, the high quality CdSe nanocrystals (NCs) capped with stearic acid were synthesized in a solvent and then purified four times by using the precipitation and redissolution process. The average size of the synthesized CdSe NCs was determined ~3.0nm via transmission electron microscopy (TEM) measurement and their corresponding optical band edge energy was also calculated as ~2.1eV using ultraviolet-visible (UV–Vis) absorption spectroscopy. The bulk heterojunction (BHJ) hybrid solar cells based on a ternary system including P3HT, PCBM and CdSe NCs at different weight concentrations (0wt%, 0.1wt%, 0.5wt%, 1wt% and 2wt%) were fabricated by spin-casting process. The effect of the concentration of CdSe NCs on the photovoltaic parameters of these BHJ organic solar cells was investigated. The surface morphology of the photoactive layer modified by the incorporation of CdSe NCs into P3HT:PCBM matrix was observed with scanning electron microscopy (SEM). It was shown that when the concentration of CdSe NCs increases above 0.1wt% in this ternary system, the photovoltaic performance of the devices significantly decreases. The power conversion efficiency of the organic photovoltaic (OPV) device was enhanced ~20% by incorporating CdSe NCs with 0.1wt% with respect to those without CdSe NCs.

Improved charge carrier dynamics in polymer/perovskite nanocrystal based hybrid ternary solar cells.

Here, brand new ternary hybrid solar cells comprising perovskite nanocrystals (NCs) with a complementary absorption profile of the organic host matrix are reported. In particular, NH2CH[double bond, length as m-dash]NH2PbI3 (FAPbI3) perovskite NCs are implemented in bulk heterojunction organic solar cells based on the pDPP5T-2 electron donating polymer and a [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) acceptor at various loading amounts and the fabricated hybrid photovoltaics are thoroughly studied by employing different optoelectrical characterization methods. Current-voltage measurements and photoinduced charge carrier extraction by linear increasing voltage (photo-CELIV) reveal improved charge generation and charge transport properties upon incorporation of perovskite NCs into the photo-active layer of the hybrid solar cell. The power conversion efficiency (PCE) of the hybrid solar cell comprising 5% perovskite NCs is 10% enhanced compared to the organic reference, mainly due to the enlarged light harvesting and increased short circuit current density (Jsc). However, results suggest that introducing a higher amount of perovskite content induces bimolecular and trap-assisted recombination in the ternary devices. We perform a comprehensive transient absorption study of the charge transfer/transport mechanisms by employing femto-second pump-probe transient absorption spectroscopy (fs-TAS). fs-TAS measurements demonstrate a slower charge carrier recombination rate due to the introduction of perovskite NCs into the photoactive layer. Results reveal that DPP injects electrons from the singlet excited state into the perovskite NCs, which causes the desired cascading charge carrier transfer. In ternary blends, a small amount of FAPbI3 NCs provides an additional pathway in favor of the charge-separated state via the NCs, which, despite accelerating the depopulation of DPP's singlet excited state slightly slows down the charge-separation process between DPP and PC61BM. Interestingly, the loss processes are slowed down; an effect that is more important and, hence, explains the improved solar cell efficiency.

Synthesis, characterization and photovoltaic performance of Mn-doped ZnS quantum dots- P3HT hybrid bulk heterojunction solar cells

Zinc sulphide (ZnS) and transition metal-doped ZnS nanocrystals were synthesized by co-precipitation method. Further the synthesized nanocrystals were characterized by Field Emission Scanning Electron Microscope (FESEM), High Resolution Transmission Electron Microscope (HRTEM), Fluorescence, UV–Visible, X-ray diffraction (XRD) and Fourier Transformed Infra-red (FTIR) Spectrometer (FTIR). Scanning electron microscope supplemented with EDAX was employed to attain grain size and chemical composition of the nanomaterials. A considerable blue shift of absorption band was noted by the manganese concentration (0.5 M) in the doped sample in comparison with ZnS quantum dots because of the decrease in the size of nanoparticles which may be due to quantum confinement. The photoluminescence emission observed at 596 nm is due to the emission of divalent manganese and can be ascribed to a 4T1→6A1 transition within the 3d shell. Though, the broad blue emission band was observed at 424 nm which may originates from the radiative recombination comprising defect states in the un-doped zinc sulphide quantum dots. XRD analysis exhibited that the synthesized nanomaterial endured in cubic structure. The synthesized nanomaterial combined with organic polymer P3HT, poly (3-hexyl thiophene) and worked in the construction of inverted solar cells. The photovoltaic devices with un-doped zinc sulphide quantum dots showed power conversion efficiency of 0.48% without annealing and 0.52% with annealing. By doping with manganese, the efficiency was enhanced by a factor of 0.52 without annealing and 0.59 with annealing. The morphology and packing behavior of blend of nanocrystals with organic polymer were explored using Atomic Force Microscopy.

TiO2 Anatase Solutions for Electron Transporting Layers in Organic Photovoltaic Cells.

Reflux of a solution of [Ti8 O12 (H2 O)24 ]Cl8 ⋅HCl⋅7 H2 O as titanium precursor at 120 °C for 24 h leads to a transparent colloidal solution of nanosized crystallized anatase TiO2 . The adjustment of the particle size and composition of the dispersant is monitored through the initial water content while controlling the conversion of propylene carbonate into propylene glycol during reflux. The solutions were processed as thin films to produce electron transporting layers in hybrid bulk heterojunction solar cells, by using a blend of P3HT:PCBM polymers as absorbers, in inverted architectures. The solutions obtained by reflux were demonstrated to produce suitable electron transporting layers.

Temperature Dependence and Impedance Characteristics of Hybrid Solar Cells Based on Poly(phenylene vinylene): ZnO Nanoparticles With Added Surfactants

A recent study has shown that the use of a semiconducting surfactant in hybrid bulk heterojunction solar cells based on poly[2-methoxy-5-(3',7'-dimethyloctyloxyl)-1,4-phenylene vinylene] and zinc oxide significantly increases their performance. To further study the mechanism underlying the improved performance resulting from the addition of a semiconducting surfactant, we compared the temperature and light intensity dependence of the current voltage characteristics and impedance spectra of devices that used no surfactant, an insulating oleic acid (OA) surfactant, or a semiconducting 2-(2-ethylhexyl)-1,3-dioxo-2,3-dihydro-1H-benzo[de]isoquinoline-6,7-dicarboxylic acid (BQ) surfactant. The temperature and light intensity dependence data enabled us to extract the activation energy for different devices, and we measured the junction resistance through impedance spectroscopy. The device that used BQ had significantly lower activation energy (9-12 meV) than that without surfactant or oleic acid (17-21 meV), thus indicating improved charge transport and consequently an increased short-circuit current. Furthermore, the impedance characteristics showed that the injection resistance, when the BQ surfactant was used, was lower than that when no surfactant or oleic acid was used. These experiments provide further evidence that the use of semiconducting surfactants is essential to improve the performance of hybrid bulk heterojunction solar cells.

Improved device performance stability of bulk-heterojunction hybrid solar cells with low molecular weight PCPDPTB

The molecular weight effect of low band-gap conjugated polymer, poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)], PCPDTBT, with an optical energy gap of Eg ∼1.4eV, on the device stability of quantum dot polymer hybrid solar cells has been studied. The PCPDTBT is integrated into hybrid polymer/QDs solar cells, where PCPDTBT acts as electron donor and CdSe QDs as electron acceptor. Morphology investigation and results on device performance over time indicate that low molecular weight PCPDTBT is preferable to fabricate high efficiency hybrid solar cells with long-term stability. An average power conversion efficiency of 2% was measured for PCPDTBT-CdSe QD devices with a molecular weight of <12kDa. The long-term stability of the photovoltaic performance of the devices was investigated and found superior compared to devices with PCPDTBT of higher molecular weight. About 96% of the PCE remained after a week of storage of solar cell devices without any further encapsulation in a glove-box. It is assumed that the improvement is mainly due to the better distribution of CdSe QDs within the polymer matrix of low molecular weight PCPDTBT in hybrid solar cells and an improved preservation of the nanomorphology of the hybrid film over time.

Influence of the dopant concentration on structural, optical and photovoltaic properties of Cu-doped ZnS nanocrystals based bulk heterojunction hybrid solar cells

Zinc sulphide (ZnS) and Cu-doped ZnS nanoparticles were synthesized by the wet chemical method. The nanoparticles were characterized by UV-visible, fluorescence, fourier transform infra-red (FTIR) spectrometry, X-ray diffraction (XRD), X-ray photoelectron spectrometry (XPS), field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM). Scanning electron microscopy supplemented with EDAX was employed to observe the morphology and chemical composition of the un-doped and doped samples. A significant blue shift of the absorption band with respect to the un-doped zinc sulphide was sighted by increasing the Cu concentration in the doped sample with decreasing the size of nanoparticles. Consequently, the band gap was tuned from 3.13 to 3.49 eV due to quantum confinement. The green emission arises from the recombination between the shallow donor level (sulfur vacancy) and the t2 level of Cu2+ . However, the fluorescence emission spectrum of the undoped ZnS nanoparticles was deconvoluted into two bands, which are centered at 419 and 468 nm. XRD analysis showed that the nanomaterials were in cubic crystalline state. XRD peaks show that there were no massive crystalline distortions in the crystal lattice when the Cu concentration (0.05–0.1 M) was increased in the ZnS lattice. However, in the case of Cu-doped samples (0.15–0.2 M), the XRD pattern showed an additional peak at 37° due to incomplete substitution occurring during the experimental reaction step. A comparative study of surfaces of undoped and Cu-doped ZnS nanoparticles were investigated using X-ray photoelectron spectroscopy (XPS). The synthesized nanomaterial in combination with poly(3-hexylthiophene) (P3HT) was used in the fabrication of solar cells. The devices with ZnS nanoparticles showed an efficiency of 0.31%. The overall power conversion efficiency of the solar cells at 0.1 M Cu content in doped ZnS nanoparticles was found to be 1.6 times higher than the reference device (P3HT:ZnS). Furthermore, atomic force microscopy and X-ray diffraction techniques were employed to study morphology and packing behavior of blends of nanocrystals and polymer respectively.

Studies on ternary zinc blend based semiconducting quantum dots for hybrid solar cell applications

A systematic study is presented in the present work on the fabrication of hybrid solar cell using doped zinc blend based semiconductor quantum dots (QDs) prepared by a simple wet chemical precipitation method. Formation of quantum dot has been ascertained by X-ray Diffraction (XRD), UV-visible Spectroscopy and Impedance Spectroscopy measurements. XRD studies established the zinc-blende phase in quantum dot regime. UV-visible studies reveal decrement in optical bandgap of the QDs with co-doping of Cd ion in ZnS lattice. Mott-Schottky analysis revealed n-type conductivity with increasein band bending from binary to ternary configuration respectively. Bulk heterojunction hybrid solar cells fabricated in 1cm X 1cm size in conjunction with p type Polypyrroleunder AM 1.5 illumination resulted in highest conversion efficiency of 1.6 %.

Constructing Post-Permeation Method to Fabricate Polymer/Nanocrystals Hybrid Solar Cells with PCE Exceeding 6.

A post-permeation method is constructed for fabricating bulk-heterojunction hybrid solar cells. Porous CdTe film is prepared by annealing the mixture solution of aqueous CdTe nanocrystals and cetyltrimethyl ammonium bromide, after which the post-permeation of polymer is employed. By this method, kinds of polymers can be applied regardless of the intermiscibility with the nanoparticles. The inorganic nanocrystals and the polymer can be treated under respective optimized annealing temperatures, which can facilitate the growth of nanocrystals without damaging the polymers. A high power conversion efficiency of 6.36% in the polymer/nanocrystals hybrid solar cells is obtained via systematical optimization.

Efficient bulk heterojunction hybrid solar cells with graphene-silver nanoparticles composite synthesized by microwave-assisted reduction

Herein, we present a simple, eco-friendly one-step microwave-assisted reduction (MWAR) that can produce silver nanoparticles (Ag NPs) and reduced graphene oxide (rGO) in the form of Ag-rGO composites for application in heterojunction hybrid solar cells. The field-effect transistor fabricated with the MWAR Ag-rGO composite showed p-type behavior with a high mobility of 3.3×105cm2V−1s−1 and conductivity of 9×106S/m which is one-order of magnitude greater than pristine graphene (i.e., 1.59×105S/m). As-synthesized Ag-rGO composite was introduced into the active layer of bulk heterojunction solar cell based on P3HT:PCBM. Compared to the P3HT:PCBM only device (i.e., control device), the Ag-rGO implemented device showed a power conversion efficiency (PCE) of 4.23%, which is about 42% increase over the control device (i.e. PCE=2.98%). This dramatic increase in PCE was found to be mainly due to an increase in short-circuit current (Jsc) from 9.55 to 12.76mA/cm2 (about 33% increase), suggesting that the incorporation of p-type Ag-rGO into the active layer enhances the charge carrier generation and fast extraction of holes to the electrode. Furthermore, the Ag-rGO composite based solar cells without encapsulation showed remarkable air stability with retaining ~90% of its original PCE and ~93% of Jsc for 30 days under ambient environment, attributed to gas barrier feature of the randomly distributed graphene sheets.

Correlation between CdSe QD Synthesis, Post-Synthetic Treatment, and BHJ Hybrid Solar Cell Performance.

In this publication we show that the procedure to synthesize nanocrystals and the post-synthetic nanocrystal ligand sphere treatment have a great influence not only on the immediate performance of hybrid bulk heterojunction solar cells, but also on their thermal, long-term, and air stability. We herein demonstrate this for the particular case of spherical CdSe nanocrystals, post-synthetically treated with a hexanoic acid based treatment. We observe an influence from the duration of this post-synthetic treatment on the nanocrystal ligand sphere size, and also on the solar cell performance. By tuning the post-synthetic treatment to a certain degree, optimal device performance can be achieved. Moreover, we show how to effectively adapt the post-synthetic nanocrystal treatment protocol to different nanocrystal synthesis batches, hence increasing the reproducibility of hybrid nanocrystal:polymer bulk-heterojunction solar cells, which usually suffers due to the fluctuations in nanocrystal quality of different synthesis batches and synthesis procedures.

CSA-doped PANI/TiO2 hybrid BHJ solar cells – Material synthesize and device fabrication

In this study, camphorsulfonic acid (CSA) doped polyaniline (PANI) synthesized by oxidative polymerization and titanium-di-oxide (TiO2) nanoparticles synthesized by sol-gel were solution blend in a mixed solvent of 1:1 m-cresol and chloroform to fabricate hybrid bulk heterojunction (BHJ) solar cells of structure ITO/PEDOT:PSS/CSA-doped PANI-TiO2/Al. The effect of TiO2 weight ratio on the cell performance was investigated by analyzing the structural and optical properties of CSA-doped PANI/TiO2 hybrid thin films with different TiO2 ratio. Crystalline structure of TiO2 nanoparticles, polymer and hybrid thin films were identified by XRD studies and root-like structure of both polymer and hybrid thin films by SEM image. CSA-doped PANI was confirmed as p-type semiconductor through Hall-effect analysis. High absorption coefficient along with PL quenching in hybrid thin film confirms its application in solar cells as photoactive layer. For optimal fabrication conditions, maximum photo conversion efficiency (PCE) of 0.21% was obtained for a device with lower TiO2 weight ratio. The results show that optimization of absorption intensity of CSA-doped PANI in the visible region of spectrum and morphology of hybrid films will effectively enhance the performance of hybrid solar cells. Error analysis of PCE for all the fabricated solar cells has been reported.

Effect of ZnO nanoparticles on the photochemical and electronic stability of P3HT used in polymer solar cells

ZnO nanoparticles are widely used as electron acceptors in hybrid polymer blend solar cells as well as electron extraction materials in organic solar cells. Here, a study of the photochemical and electronic stability of poly(3-hexyl thiophene)/zinc oxide nanoparticle (P3HT/ZnO) interfaces is presented. Photostability is compared with device stability of hybrid bulk heterojunction solar cells under light soaking and dark storage. We first investigate the photocatalytic properties of ZnO in P3HT:ZnO blend layers. The results indicated that the photocatalytic activity of ZnO nanoparticles drastically increases the photooxidation rate of P3HT. Photostability of P3HT:ZnO active layers was significantly improved when irradiation was performed in absence of UV radiations and in absence of oxygen. Using optimal conditions to avoid photodegradation during light soaking still leads to rapid performance losses revealing device degradation is not related to photodegradation of the hybrid polymer blend but to electronic modification during illumination. Importantly, both dark storage in air as well as light soaking experiments show that the stability of interfaces between P3HT and ZnO nanorods is higher than that observed in devices using ZnO nanospheres. This points towards the importance of the shape of the ZnO nanoparticles for long time stability in polymer solar cells.

Copper oxide hole transport materials for heterojunction solar cell applications

In this study, polymer:fullerene bulk-heterojunction hybrid solar cells with the structure, fluorine-doped tin oxide (FTO)/Cu2O/poly (3-hexylthiophene): 6,6-phenyl-C61-butyric acid methyl ester (P3HT:PCBM):TiO2/Ca/Al, were fabricated. The effect of a p-type Cu2O thin layer deposited between the active layer (P3HT:PCBM) and the FTO layer on cell performance was investigated; the p-type Cu2O thin layer was deposited through thermal evaporation. The results showed that the Cu2O interfacial layer increased the efficiency and stability of the hybrid solar cells. The optimal performance was obtained for the solar cell structure FTO/Cu2O (10nm)/P3HT:PCBM:TiO2 (15wt.%)/Ca/Al (best cell structure), which had the following specifications: open-circuit voltage=0.58V, short circuit current density=12.14mA/cm2, fill factor=58.63%, and η=4.13%. The Cu2O layer prevented the rapid degradation of the interface, thereby increasing the lifetime of the hybrid solar cells.

Synthesis and characterization of tin disulfide nanocrystals for hybrid bulk hetero-junction solar cell applications

SnS2 nanoparticles (NPs) were synthesized using a modified hot injection method, and the morphological, structural, optical properties and chemical composition of the SnS2 NPs were characterized using a range of analysis techniques. Transmission electron microscopy (TEM) revealed distorted-hexagonal shape and particle size of the assynthesized nanoparticles. X-ray diffraction (XRD) showed that the SnS2 NPs had high crystallinity with hexagonal structure. Ultravioletvisible (UV-vis) absorption spectrum revealed an absorption band at 440nm due to SnS2 nanoparticles. Solar cell devices based on the blending of a conjugated polymer as a donor material and SnS2 (NPs) as an acceptor material were fabricated, and the device performance was tested. The solar cell efficiency was improved by optimizing the thickness of active layer containing the well-controlled SnS2 NPs, and increasing the light harvesting using a low band gap polymer. The results indicate that the SnS2 NPs can be good candidate materials for bulk hetero-junction (BHJ) solar cells.

Simple and Green Synthesis of Lead Sulfide Nanocrystals for Hybrid Bulk Hetero-Junction Solar Cells

Simple and Green Synthesis of Lead Sulfide Nanocrystals for Hybrid Bulk Hetero-Junction Solar Cells

P-type semiconductor surfactant modified zinc oxide nanorods for hybrid bulk heterojunction solar cells

In this work, hybrid bulk heterojunction solar cells based on surfactant-modified zinc oxide nanorods (ZnO NRs) blended with poly-(3-hexylthiophene) (P3HT) are presented. (E)-2-cyano-3-(5′-(4-(dibutylamino)styryl)-2,2′-bithiophen-5-yl)acrylic acid (1), a p-type semiconductor, is used as grafted interfacial surfactant on ZnO NRs, named 1-ZnO NRs, in order to improve simultaneously the nanoscale morphology of the hybrid polymer blend as well as the electronic properties of the heterojunction interface. Our studies reveal that the ligand modification of ZnO NRs leads to strongly improved aggregate free P3HT/ZnO blends that show five time increased power conversion efficiency and corresponding photo-generated charge carrier transport compared to untreated ZnO NRs. From transient absorption spectroscopy, it was found that recombination kinetics were similar in the device using untreated ZnO and modified 1-ZnO NRs, respectively, pointing to a major impact of the ligand in the improvement of the blend morphology. Corresponding device optimization led to improvements of FF and Voc to values comparable to P3HT blends using fullerene acceptors, but photocurrent density of the P3HT/1-ZnO solar cells was found low even after optimization. The latter could be addressed to destruction of long range organization of P3HT induced by the presence of the ZnO NRs as well as low electron transport inside the blend.

Performance Enhancement of Bulk Heterojunction Hybrid Solar Cell Using Macroporous Silicon

This article focuses on the work which deals with the effect of introducing macroporous silicon as the cathode of hybrid solar cell. This work shows that the photocurrent of bulk-heterojunction hybrid solar cell can be enhanced by using macroporous silicon (macro-PSi) as the cathode that provided increased effective contact surface area at the interface of organic-inorganic material. The organic compound (3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) polymer blend at 1:1 ratio was used to fabricate the solar cell. It was found that the pore-diameter of the porous silicon plays an important role on short-circuit current of the fabricated hybrid solar cell. Huge enhancement of short-circuit current density (~ 73 times) was obtained when the average pore diameter of macro-PSi was comparable to the photogenerated carrier transport length of the photoactive polymer. The annealing of the whole structure further enhanced the overall performance of the fabricated hybrid solar cell.

Adsorption of porphyrin and carminic acid on TiO2 nanoparticles: A photo-active nano-hybrid material for hybrid bulk heterojunction solar cells

A photo-active nano-hybrid material consisting of titania nanoparticles, carminic acid, and sulphonic acid functionalized porphyrin is reported here. In an attempt to extend the absorption spectrum of titania to visible region by co-adsorbing carminic acid and sulphonic acid functionalized porphyrin on its surface. Interesting changes in the UV–visible and fluorescence spectra were noticed. The adsorption of carminic acid resulted in the formation of charge transfer complex with titania nanoparticles. This was confirmed by the electronic absorption and fluorescence emission spectroscopies. Chemisorption of porphyrin on the carminic acid functionalized titania further boosted the charge transfer effect. This was noticed by the increase in intensity and width of the charge transfer absorption and emission bands. Energy level diagram showed that the interaction among the constituents of the nano-hybrid assembly permitted the flow of electron in a cascade manner from carminic acid to TiO2.This also allowed direct flow of electrons either from carminic acid or porphyrin toward titania. The material was used as an active blend in hybrid bulk heterojunction solar cells. Co-functionalized TiO2-based devices were found 3.5 times more efficient than the reference device but morphology of the device proved a major setback.

Functionalized silicon nanowires/conjugated polymer hybrid solar cells: Optical, electrical and morphological characterizations

We investigate the effects of Si nanowires surface modification with polystyrene (PS) on the performance of bulk heterojunction hybrid solar cells based on poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene] (MEH-PPV) and PS-SiNWs. The optical, electrical and morphological properties of these hybrid nanocomposites have been investigated. Due to charge transfer efficiency, improved electrical coupling between SiNWs and MEH-PPV and homogeneous dispersion of functionalized SiNWs, the performance of studied photovoltaic structure shows a significant improvement with the progressive addition of PS-SiNWs. With polystyrene surrounded SiNWs as acceptor materials, the device typically shows a JSC of 7.36µA/cm2, VOC of 0.87V and a FF of 48% for the composition MEH-PPV:PS-SiNWs (1:4).