A new efficient porphyrin-type photoabsorber for vacuum-processed organic solar cells

Physical processes in organic solar cells

Benzodithiophene-Based Small-Molecule Donors for Next-Generation All-Small-Molecule Organic Photovoltaics

Charge transfer and charge extraction mechanisms are two prevalent issues in the growing field of organic solar cells. Due to their complexity in nature, new methods need to be involved in addressing the fundamental properties associated with organic polymer solar cells. This dissertation has focused on developing a new method to estimate the charge collection lengths and surface recombination lengths of organic polymer solar cells. Photocurrent spectra have been analyzed systematically to observe the dependence on thickness of the active material. A red shift of the peak of the normalized photocurrent with respect to the device thickness has been further analyzed for two major material systems used in organic polymer solar cells, namely MDMO-PPV: PCBM and P3HT: PCBM. A theoretical model that measures the charge extraction of bulk hetero junction solar cell structures has been used taking into account of three main parameters including charge carrier collection length, absorption variation and surface recombination. This model has led to estimate two important parameters associated with charge transfer, recombination and extraction of organic solar cells which will provide opportunities for improvements in the performance of organic electronic devices. Key results are summarized as follows. A complete analysis of photocurrent spectra has been done to see its variation with active material thickness of well-known two material systems of bulk heterojunction organic solar cells. Results of these preliminary measurements suggest that peak of the photocurrent for both systems red shift with increasing thickness. Charge extraction model is introduced to explain the initial red shift of the photocurrent. This model fits well with the experimental results. Further analysis of the model suggests that the charge collection lengths can be estimated for organic polymer structures. Theoretical model gives higher collections lengths for MDMO-PPV solar cells while a lower collection length for P3HT solar cells. This model also has the capability to estimate the surface recombination length of organic bulk heterojunction solar cells. Different interfacial layers have been used to fit to the model calculation. These results suggest that the least surface recombination lengths were achieved with solar cells of PEDOT-PSS. This method can be used to optimize the interfacial layers to improve the efficiency in organic solar cells. AC photocurrent measurements have been carried out to observe the frequency dependence of organic solar cells. Main results show that increasing response time from the light source increases the performance of the solar cells. Further analysis of these

Since their inception, organic solar cells have been a cynosure of photovoltaic (PV) community, owing to their simplicity, affordability and mass-production capabilities. Research on organic solar cells has been propelled by advances in nanotechnology, polymer synthesis, and semiconductor processing; efforts to achieve high power conversion efficiencies (PCE) through refined device geometry, tailored synthesis and/or combination of new low-bandgap materials, and heuristic process optimization have fructified as ~10 % efficiency in single-junction organic solar cells. Recent PCE enhancement in organic solar cells has mostly attributed to the development of small bandgap materials that extend absorption of the sun into the red and infrared wavelengths.Utilizing tandem cells comprised of both large and small bandgap sub-cells enables light harvesting of different parts of the solar spectrum to be separately optimized, yielding higher PCE than single junction solar cells. But the challenges in achieving highly efficient organic tandem solar cells include optimal combination of materials for each sub-cell and interconnecting layers between sub-cells that are process compatible. Optimal combination of materials can be achieved by selection of two materials having complementary absorption windows. The interconnecting layer provides electrical and optical coupling between the two sub-cells and plays a key role in the performance of tandem cells. For the design of the interconnecting layer, electrical, optical, chemical and structural characteristics should be considered. Ideally, it should effectively facilitate charge transport between two sub-cells. Moreover, high transmittance and negligible absorption in the spectral region where two sub-cells absorb is desirable. Last but not least, the interconnecting layer should be designed to survive the subsequent solution coating and provide conformal surface coating for tandem cells with solution processed top cells. Here we evaluate some of candidate metal oxides for tunnel junction layers for organic tandem solar cells. Metal oxides are grown by Atomic Layer Deposition (ALD) for thin defect-free conformal layer to circumvent miscibility issues and negligible absorption. Normal and inverted interfaces are examined. The influence of annealing under different conditions and methods will be presented. Tunneling properties are qualified by J-V characteristics and optical properties evaluated by UV-Vis are contrasted to suggest optimal design tradeoffs of tunnel junctions for solution processed organic tandem solar cells.

In today’s technologically advanced era, our society needs an eco-friendly technology that is efficient and at the same time has low manufacturing cost. Solar energy is one of the major sources of renewable energy entering the earth’s atmosphere in bulk. It is a fact that the amount of solar energy lighting up the earth’s land mass over a year is around 3000 times the total amount of annual human energy use. Fossil fuels are very limited and we would not be able to use it in upcoming future. Among many materials used for fabrication of solar cells in the current and past century, the organic solar cells are good solution to low cost energy production. So, new photovoltaic energy conversion technology can contribute to environment friendly renewable energy production and reduction of CO 2 emission associated with fossil fuel and biomass. Organic photovoltaic solar cells deal with conductive polymer or small organic molecules. This type of solar cell has attracted attention of the photovoltaic industry in past few years because of its flexibility in usage, low manufacturing cost and abundance in material than first and second-generation photovoltaic technology. Many researchers have investigated on the various materials of the organic solar cells. In 1986, when first organic solar cell was fabricated, it had the efficiency of 1.1%. Now the laboratory efficiency of solar cell has been reported of the order of 11%. This paper reviews the technological progress of organic solar cells as a cheap and eco-friendly conversion of solar energy to electricity. Keywords: Photovoltaic energy conversion, organic solar cell, solar cell fabrication materials Cite this Article Farheen Naaz, Usha Bajpai. Organic Solar Cells: A Technological Review. Journal of Alternate Energy Sources and Technologies . 2017; 8(1): 18–22p.

Photovoltaic technology has a range of applications nowadays. Organic solar cell research has developed in recent years. Common materials for organic solar cells are phthalocyanines. In this paper it is presented a discussion of the fundamentals of photovoltaic technology, photovoltaic effect, organic solar cells, phthalocyanines and Gallium Arsenide reconstructed surfaces. Also it is studied the behavior of lead pthalocyanine (PbPc) in substrates of Gallium Arsenide-GaAs (001) with reconstruction surface Arsenide (As) stoichiometric β2(2x4). It is an analysis and study of innovative organic solar cells. The reason for this study is that PbPc is an organic molecule with very good optoelectronic properties, promising to be used in organic thin film solar cells or combination of organic and inorganic layers solar cells. In research is the behavior of phthalocyanines according to the surfaces of the substrates. The experimental photovoltaic characterization of a solar cell from lead phthalocyanine is presented. The efficiency of potential solar cells is estimated by measuring the photocurrent spectra. The understanding of the material and the samples combinations is important for potential applications and improvements for the use of solar cells.

Photovoltaics literature survey (No. 181)

The effect of magnetic field on the photocurrent generation of three main types of solar cells with entirely different structures, i.e., organic, dye-sensitized and silicon solar cells, is investigated. The magnetic field effect on photocurrent (MPC) signals of organic and dye-sensitized solar cells are estimated by fitting experimental data with a single non-Lorentzian. For the first time, the MPC signal of a silicon solar cell is theoretically obtained and proved by performing a novel analysis of electromagnetic force produced by external magnetic field. Experimental results are given that explicitly verify the theoretical results, in particular, the correctness of the MPC signal obtained in this study. To provide a clear and concise conclusion deduced from experimental data and theoretical analyses presented in this research work, the MPC signals of organic, dye-sensitized and silicon solar cells are also compared. The comparison demonstrates that external magnetic field causes an increase in the photocurrent density of a bulk-heterojunction organic solar cell, while its impact on dye-sensitized and silicon solar cells is negative, i.e., it causes a reduction in their photocurrent density. Thus, under influence of unavoidable external magnetic fields, organic solar cells are more efficient and advantageous compared to dye-sensitized and silicon solar cells.

Many absorber materials used for the fabrication of organic solar cells cover a rather narrow wavelength region in their Spectral Response (SR). Therefore, the use of several absorbing layers with different SR in multi-junction solar cells is of high benefit in order to cover a wider part of the solar spectrum and, in addition, can be realized with a straightforward extension of the manufacturing process of single junction devices. Thus, recently organic multi-junction devices have gained great interest and attracted a broad research activity. In consequence, precise and reliable determination of the performance parameters of such devices constitutes an increasing demand at calibration laboratories such as Fraunhofer ISE CalLab PV Cells. The presented procedures allow for determining solar cell parameters of such technologies in accordance to standard test conditions (STC) traceable to international units. The existing experience with measuring III-V multi-junction solar cells at Fraunhofer ISE with a multi-source solar simulator was translated to measurements on encapsulated thin film organic multi-junction solar cells manufactured within a cooperation of Heliatek GmbH and IAPP. The paper reports the methodology of the calibration of a multi-junction organic solar cell. The SR of the component cells were determined applying suitable LED bias light and a reverse bias voltage chosen to prevent measurement artefacts. With the results we were able to perform a spectrometric characterization for this organic tandem solar cell and verify that a close current matching under the AM1.5g spectrum was achieved. The knowledge of the current at the current matching point enables to calculate the absolute SR of the sub cells. Also specific considerations which have to be taken into account when measuring encapsulated thin film (e.g. organic) solar cells will be discussed.

In this presentation, we introduce our recent research progress on organic and perovskite solar cells using functionalized nanocarbon materials. We applied wet-processed scalable single-walled carbon nanotubes (SWCNT) films to transparent and back electrodes in organic solar cells for large area solar cells. Gas-phase growth SWCNT was dispersed with sodium dodecylbenzenesulfonate surfactant in an organic solvent and solution-coated on a treated glass substrate to make a SWCNT film as a transparent electrode. We achieved the first high efficiency e-DIPS/wet-processed SWCNT film electrode in organic solar cells with a best-efficiency of 5.93% through the optimized HNO3 doping methodology.We also report enhanced hole-transporting ability of widely utilized poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) achieved by applying cationic nitrogen-doped graphene (CNG) as a p-type modifier for efficient organic solar cells. The power conversion efficiency of the CNG-coated PEDOT:PSS-applied OSC reaches 2.76% using poly(3-hexylthiophene), which is an increase of 40% compared to that of the pristine PEDOT:PSS-applied OSC (1.96%). This technology improved the efficiency of organic solar cells using a low-bandgap polymer from 6.54% to 7.79%. The significantly enhanced performance is contributed by the increased hole-transporting ability, and the improved interfacial morphology of PEDOT:PSS.

As organic solar thin films fabricated by an active layer of organic materials are economical, lightweight, and flexible, as well as facilitating processing, organic solar cells have attracted considerable attention within the past few decades as a clean energy source. With this in mind, there have been global investigations and studies of the power conversion efficiency (PCE) within organic solar cells. In organic thin-film solar cells, the effect of the performance is not only dependent on an adopted active material but also the molecular orientation on the electrode. Using the mixed solution of Poly (3-hexylthiophene) and PCBM, both dissolved by solvent, an organic thin film is fabricated using the paint method (The conceptual diagram of the paint method is shown in Fig. 1) The form of the thin film was evaluated, an organic thin-film solar cell using the paint method for the active layer was made, and its performance was evaluated and examined. Using the mixed solution of Poly(3-hexylthiophene) and PCBM, both dissolved by solvent, an organic thin film is fabricated using the paint method (The conceptual diagram of the paint method is shown in Fig. 1) The morphology of the thin film was evaluated using an AFM image, UV/vis spectra, and so forth. Based on these data, an organic thin-film solar cell that used the paint method for the active layer was fabricated, and the performance was evaluated and examined. For the organic thin film solar cell fabricated using the brush painting method, the open-circuit voltage (Voc) is 0.41 V, the short circuit current density (Jsc) is 2.07 mA/cm2, and the fill factor is 0.34. The efficiency η of PCE becomes 0.29%.

Morphology control and device optimization for efficient organic solar cells

As organic thin film solar cells fabricated by the active layer of organic materials are economical, lightweight, and flexible, as well as generating no CO 2 and being easy to fabricate, they have attracted significant attention as green energy sources from a past decade to date. Therefore, their power conversion efficiency (PCE) has been investigated and studied worldwide. In organic thin-film solar cells, the effect of the performance depends not only on the adopted active material but also relates to the molecular orientation on the electrode. Using a mixed solution of Poly(3-hexylthiophene) and PCBM, both of which were dissolved in a solvent, the organic thin films were fabricated using the paint and spray methods, while the morphology of the thin film was evaluated by an AFM image, UV/vis spectra, and so forth. Based on these data, an organic thin-film solar cell using both solution methods for the active layer was fabricated, and the performance evaluated and examined. For organic thin film solar cells fabricated using a spin-coating method, the open-circuit voltage (Voc) is 0.41V, the short circuit current density (Jsc) is 2.07mA/cm 2 , and the fill factor is 0.34, while the efficiency η of PCE become 0.29%. In the spray method, the short circuit current (Isc) is 2.5 mA/cm 2 , the open circuit voltage (Voc) is 0.45 V, the fill factor (FF) is 0.28, and the power conversion factor (PCE) 0.35%. The area of organic solar cells fabricated by spin coating and spray methods is 1 cm 2 respectively. The organic solar cells are not thermally treated, and hence have high respective power conversion efficiencies.

Oligothiophene-based photovoltaic materials for organic solar cells: rise, plateau, and revival

Organic photovoltaic solar cells consist of organic semiconductors have attracted valuable importance in the areas of electronics and photonics during the last decade. Organic semiconductors are more flexible and less expensive substitute to inorganic semiconductors. By using simple and environmental friendly techniques, organic solar cells provide the possibility of fabricating large area, cost-effective, flexible, light-weight devices. An organic solar cell consists of an organic active layer which consider the basic steps in photovoltaic conversion such as light absorption, charge carrier generation, charge carrier transport and injection of charge carriers through the contact electrodes. Effect of Rs and Rsh in equivalent of circuit of photovoltaic diode discussed. P3HT:PCBM use as promising material for active layer. Stability and power conversion efficiency might be step-downs. By reducing these main challenges organic thin film solar cell can be part of solar cell market. Graphene sheet has great quality to replace indium tin oxide as cathode material. For simulation of bilayer organic solar cell determined that getting optimizing efficiency by maximizing values of exciton diffusion range, necessity of increase in electron hole mobility by applying horizontally external electric field, and lesser the donor accepter interface. Bulk heterojunction maximise the donor-acceptor contact area compare to bilayer heterojunction organic solar cell.