Stability Of P3HT Research Articles

Influence of ZnO nanoparticles as electron transport material on the performance and stability of organic solar cells with sputtered Ag back electrodes

ZnO has been widely used as electron selective material in P3HT:PCBM organic solar cells with either conventional or inverted architecture in order to enhance the extraction of electrons and block the collection of holes at one electrode. In this work we investigate the influence of ZnO nanoparticles electron transport layer (ETL) on the performance and stability of P3HT:PCBM based organic solar cells with conventional architecture and magnetron sputtered back Ag contacts. Their stability in the dark and under real outdoor conditions was monitored by current-voltage measurements and impedance spectroscopy. The impedance spectra were taken as a function of applied bias under illumination in order to reveal more information about the degradation mechanisms taking place in the device.

Optimization of annealing temperature and the annealing effect on life time and stability of P3HT:PCBM-based organic solar cells

Post-production annealing which improves the power conversion efficiency of the P3HT:PCBM-based organic cells are very important process. Lots of various annealing temperatures and annealing times have been used for annealing process in previous studies but not any criteria was taken as a basis for determination of annealing temperature. In this study annealing temperature was optimized for annealing time of 3 min ITO-PEDOT:PSS/P3HT:PCBM/Al was fabricated at the weight ratio of 12:8 for P3HT:PCBM. Organic solar cells were annealed at different annealing temperatures in the range of 80 °C–160 °C. The variation of external quantum efficiency (EQE) with annealing temperature was obtained. The higher EQE was obtained at 120 °C. Thus, 120 °C was determined as optimum annealing temperature. The aging experiments were performed under constant humidity, illumination and atmospheric conditions. It has been observed that the post- product annealed at 120 °C solar cells have more longer life time and more stable compared with the non-annealed cell and other annealed solar cells.

The effects of the PEDOT:PSS acidity on the performance and stability of P3HT:PCBM-based OSCs

The optical transmittance, electrical conductivity and morphology of PEDOT:PSS treated with ammonium hydroxide (NH4OH) have been investigated. Transmittance spectra of spun PEDOT:PSS layers were enhanced slightly as a result NH4OH treatment while surface of the films has exhibited variation in the roughness and an increase in the electrical conductivity. Improvement in the physical properties of PEDOT:PSS is shown to be the key factor in enhancing the power conversion effeciency (PCE) with values as high as 4% associated with high fill factor (FF) of 57%, open circuit voltage (VOC) of 0.64 V and larger short circuit current density (JSC) of 11 mA cm−2. Stabiltiy test of the devices has been carried out over a period of 2 months, when a device incorporating PEDOT:PSS with pH ~ 4 as the hole transport layer has shown an improved stability with a degredation in PCE in about 43% whereas JSC has decreased in about 20% compared to a device incorporating pristine PEDOT:PSS with PCE decreased in about 66% and JSC in about 50% over the stated period of test. These effects have been ascribed to the increased acidity of the hole transport layer.

Solution stability of active materials for organic photovoltaics

The solution stability of the active materials poly(3-hexylthiophene) (P3HT), [6,6]-phenyl C61 butyric acid methyl ester (PCBM), and P3HT:PCBM blends were studied by a combination of organic photovoltaic (OPV) device performance, ultraviolet–visible (uv–vis) spectroscopy, and simulation calculations. OPV devices based on the structure ITO/PEDOT:PSS/Active layer (P3HT:PCBM)/Al showed that pure P3HT, pure PCBM, and P3HT:PCBM blend solutions could be stable for as long as one month when stored in either a glovebox or in air. Especially, P3HT:PCBM solution blends are much more stable than P3HT or PCBM solutions stored separately, in which the former could be stored stably over two months. The addition of PCBM to P3HT solution forms P3HT:PCBM dimers, avoiding the formation of charge transfer complexes. The calculation results showed that the electronic wave-function of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) are isolated in P3HT:PCBM dimers. The research provides a new understanding on the stability of P3HT and P3HT:PCBM solutions, and has great practical application in the fabrication of large-area OPV modules by printing or coating techniques.

Interface modification of polymer solar cells using graphene oxide and TiO2 NPs

The photovoltaic behavior and stability of P3HT:PCBM bulk heterojunction polymer solar cells (PSCs) were studied in detail, in which graphene oxide (GO) and TiO2 nanocrystalline particles (TiO2 NPs) were used as hole transport layer (HTL) and electron transport layer (ETL), respectively. The power conversion efficiency (PCE) of PSC devices with the GO as the HTL reached 3.09%, which is comparable to those using the PEDOT:PSS as the HTL. The PCE was further improved by using TiO2 NPs buffer layer as the ETL and reached 3.32%. The interface capacitance analysis and electrochemical impedance measurement confirmed that the GO as the HTL in PSCs has better interface properties than the PEDOT:PSS. The device stability showed that PSCs with the GO layer are much more stable than those with the PEDOT:PSS layer. The PCEs of PSC devices with both GO and TiO2 NPs layers could retain 60% of its initial value after 180 h exposure in high humidity atmospheric environment (air humidity ∼80%). The study showed that the combination of GO and TiO2 NPs acted as the HTL and ETL, respectively, has the potentials for preparing efficient and stable PSCs devices, which can match with the printing or coating techniques.

Insights into the stability and thermal degradation of P3HT:C60 blended films for solar cell applications

This paper demonstrates the changes in the nanoscale morphology of the blended films induced by a diffusion of C60 molecules and degradation during longer thermal treatment above the glass transition temperature (130 °C). The results showed that the film morphology, including the size and population of poly(3-hexylthiophene) (P3HT) crystallites, rapidly reduced with annealing time. A large-scale (>1μm) C60 aggregation, demonstrating a bulky phase separation between the polymer and C60, was identified after 5 h annealing, which resulted in a degradation of charge carrier mobility and conductivity. X-ray diffraction verifies that the interchain packing of P3HT within the crystallized phase improved with an increasing in annealing time, but the volume fraction of the P3HT (100) phase normal to substrate increased up to 3 h and decreased at longer annealing times resulting in the ageing of the films. Changes in the infrared spectra of the extended annealed samples were recorded and the oxidation products were identified. A degradation mechanism that accounted for the modifications in the infrared spectra and a detachment of the hexyl chain from P3HT was demonstrated, resulting in chain cutting, conjugation loss and a reduction in the UV–vis absorbance. The morphology change with the annealing time resulted in an abrupt decrease in the PCE of P3HT:C60 solar cells. These findings signify that the stability of P3HT:C60 solar cells cannot be secured for longer annealing period owing to the unsettled morphology.

Abrupt Morphology Change upon Thermal Annealing in Poly(3‐Hexylthiophene)/Soluble Fullerene Blend Films for Polymer Solar Cells

AbstractThe in situ morphology change upon thermal annealing in bulk heterojunction blend films of regioregular poly(3‐hexylthiophene) (P3HT) and 1‐(3‐methoxycarbonyl)‐propyl‐1‐phenyl‐(6,6)C61 (PCBM) is measured by a grazing incidence X‐ray diffraction (GIXD) method using a synchrotron radiation source. The results show that the film morphology—including the size and population of P3HT crystallites—abruptly changes at 140 °C between 5 and 30 min and is then stable up to 120 min. This trend is almost in good agreement with the performance change of polymer solar cells fabricated under the same conditions. The certain morphology change after 5 min annealing at 140 °C is assigned to the on‐going thermal transition of P3HT molecules in the presence of PCBM transition. Field‐emission scanning electron microscopy measurements show that the crack‐like surface of blend films becomes smaller after a very short annealing time, but does not change further with increasing annealing time. These findings indicate that the stability of P3HT:PCBM solar cells cannot be secured by short‐time annealing owing to the unsettled morphology, even though the resulting efficiency is high.