Low-cost Organic Solar Cells Research Articles

Acceptor molecules with different central and terminal units for P3HT based solar cells: Effects of the molecular structures on their properties

The design strategy of acceptor materials matched with poly(3-hexylthiophene) (P3HT) is highly desired for the development of low-cost organic solar cells (OSCs). Herein, we introduced strong electron-donating central units and weak electron-withdrawing end groups to construct the acceptors with high HOMO and LUMO, modulated the molecular symmetry and conjugation length by changing the structures of central units, and synthesized six acceptor molecules, namely, TDTC-O2F, TTDTC-O2F, TTTDTC-O2F, TDTC-ThBr, TTDTC-ThBr and TTTDTC-ThBr. The high LUMO energy level of the acceptors endowed the P3HT based OSCs with relatively high Voc values. Molecular symmetry, conjugation length of central units and the terminal structure jointly affect the molecular crystallinity and miscibility of the blends. Owing to the proper film morphology, the P3HT:TTDTC-ThBr based devices achieved the champion power conversion efficiency of 6.15 %.

Optimizing molecular conformation and photovoltaic property of simple asymmetrical SMAs by tuning electron-donating central subunit

To overcome complex synthetic routes of multiple-fused-ring small-molecule acceptors (SMAs), it is crucial to develop simple fused-ring and non-fused-ring SMAs and explore structure-property relationship for high-efficiency and low-cost organic solar cells (OSCs). For this purpose, a novel SMA named BIO-4Cl was designed and synthesized, which consist of an asymmetric dual electron-donating D-D′ central block of alkoxy- indenothiophene (INT) and benzodithiophene (BDT), as well as two electron-accepting (A) terminal group of 2-(5,6-dichloro-3-oxo-2,3-dihydro-1 H-inden-1-ylidene)malononitrile. The effect of the electron-donating D-D′ central block on molecular conformation, absorp- tion, energy level, mobility, morphology and photovoltaic performance of the SMAs was primarily studied by integrating its analogue IOEH-4Cl with the cyclopentadithiophene (DTC) and INT central block. By altering the electron-donating D′ subunit in the D-D′ central block, it is found that BIO-4Cl and IOEH-4Cl behave different molecular conformation with the S-type and C-type, respectively. As a result, BIO-4Cl exhibits a blue-shifted absorption with a decreasing molar extinction coefficient, as well as a low HOMO and LUMO energy level in comparison with IOEH-4Cl. The IOEH-4Cl blend film displays better crystallinity and film morphology than the BIO-4Cl blend film using polymer PM6 as donor material. The IOEH-4Cl-based OSCs display better photovoltaic property than the BIO-4Cl-based OSCs, in which the power convention efficiency (PCE) was increased 4.75 times to 13.7%. This work indicates that fine-tuning the electron-donating subunit in an asymmetric dual electron-donating D-D′ central block is crucial to optimize molecular conformation and PCE for simple-structure asymmetric SMAs.

A Review on Current State, Recent Developments and Future Prospects of Dye Sensitized Solar Cells

The sun is a primary abundant renewable source of energy for most of the life forms in our planet. By fully grasping the power of the sun, we can improve our way of life, reduce our dependence on fossil fuels or other types of energy sources and stimulate economy by bringing new jobs to all our planet industry. Among sustainable and renewable energy sources, solar cell, also known as photovoltaic cell, is one of the promising options of renewable energy and the most efficient. For the past several years, different photovoltaic devices like inorganic, organic and hybrid solar cells are invented for different application purposes. Regardless of its high conversion rate of silicon-based solar cells, the high module cost and complicated production process restricted their application. Research has been focused on alternative organic solar cells for their inherent low module cost and easy fabrication processes. Dye sensitized solar cell (DSSC) is considered to be one of the most promising, efficient, low-cost organic solar cells in recent years. DSSC, being transparent to some extent and comparatively cheaper than conventional solar photo-voltaic, can be a potential energy source for the future. This review paper focuses on the working of DSSC, its current state and recent developments in the various components of DSSC. The perspectives for the future development of the technology have also been discussed.

Comparative study on thermally evaporated and solution processed cathode modifying layers in organic solar cells

Organic solar cells have been fabricated using cathode modifying layers of thermally evaporated bathophenanthroline (Bphen), ytterbium doped Bphen (Bphen:Yb), and solution processed (N,N-dimethyl-ammonium N-oxide) propyl perylene diimide (PDINO). Compared to pristine Bphen, Bphen:Yb shows higher electron mobility and thereby increases fill factor of device, demonstrating the weak n-doping of Yb in Bphen. As a result of Fermi level pinning, Bphen:Yb forms an ohmic contact with photoactive layer, underpinning efficient electron injection and extraction of device. Compared to conventional PDINO, despite lower electron mobility, Bphen:Yb enables increased optical absorption of device and smoother morphology of device, thereby improving power conversion efficiency of device. The current research points out that the integration of thermally evaporated weakly n-doped cathode modifying layer and solution processed photoactive layer is a promising method to fabricate high-efficiency and low-cost organic solar cells.

High-performance and low-cost organic solar cells based on pentacyclic A–DA′D–A acceptors with efficiency over 16%

Developing high-performance and low-cost donor/acceptor materials is crucial for the industrialization of organic solar cells (OSCs).

Exciton and Charge Carrier Dynamics in Highly Crystalline PTQ10:IDIC Organic Solar Cells

AbstractHerein the morphology and exciton/charge carrier dynamics in bulk heterojunctions (BHJs) of the donor polymer PTQ10 and molecular acceptor IDIC are investigated. PTQ10:IDIC BHJs are shown to be particularly promising for low cost organic solar cells (OSCs). It is found that both PTQ10 and IDIC show remarkably high crystallinity in optimized BHJs, with GIWAXS data indicating pi‐pi stacking coherence lengths of up to 8 nm. Exciton‐exciton annihilation studies indicate long exciton diffusion lengths for both neat materials (19 nm for PTQ10 and 9.5 nm for IDIC), enabling efficient exciton separation with half lives of 1 and 3 ps, despite the high degree of phase segregation in this blend. Transient absorption data indicate exciton separation leads to the formation of two spectrally distinct species, assigned to interfacial charge transfer (CT) states and separated charges. CT state decay is correlated with the appearance of additional separate charges, indicating relatively efficient CT state dissociation, attributed to the high crystallinity of this blend. The results emphasize the potential for high material crystallinity to enhance charge separation and collection in OSCs, but also that long exciton diffusion lengths are likely to be essential for efficient exciton separation in such high crystallinity devices.

Indoor/outdoor light-harvesting by coupling low-cost organic solar cell with a luminescent solar concentrator

The use of luminescent solar concentrators (LSCs) is considered a promising solution for harvesting indoor and outdoor light energy. Despite a multitude of investigations of LSC based photovoltaic (PV) systems, few reports are available on LSCs for emerging PVs, such as third-generation PV technologies. To fill this gap, we develop a novel LSC based PV device by coupling an LSC with a low-cost organic solar cell. The LSC is fabricated by employing different concentrations of organic luminophores, while a polymer/fullerene-based photoactive layer is prepared for the organic PV (OPV) device. With proper spectral matching, our champion LSC-OPV device exhibits optical efficiency (ηopt) and power conversion efficiency (ηPCE) of 6.10% and 0.51% under light-emitting diode (LED) illumination, respectively. Further, performance evaluation under 1sun illumination implies the ηopt and ηPCE of 8.5% and 0.17%. We also perform the color analysis of LSC-OPV devices which shows that such devices are aesthetically feasible for use in indoor and outdoor conditions. Thus, this study highlights the substantial opportunity for the rational design of hybrid LSC-PV systems where third-generation PVs are viable prospects.

Achieving an Efficient and Stable Morphology in Organic Solar Cells Via Fine-Tuning the Side Chains of Small-Molecule Acceptors

Both the efficiency and stability of low-cost organic solar cells are central components for meeting the requirements of commercialization for organic photovoltaics (OPV). Furthermore, the relation...

Solution processed hole transport layer towards efficient and cost effective organic solar cells

In this work, we report Copper Sulfide (CuS) as a solution processed, inexpensive and effective hole transport layer (HTL) for efficient and low cost organic solar cells. These devices were fabricated using two most studied low band gap donor materials PTB7 and PCDTBT blended with PC71BM as an acceptor material. We have used a simplest device architect such as ITO/CuS/active layer/Al at ambient conditions. The power conversion efficiencies (PCEs) of these devices have been achieved to up to 4.32% and1.76 % for PTB7 and PCDTBT based devices respectively. Finally, we have provided a further example of solution processable CuS as an effective HTL for solution processable organic photovoltaic applications.

Improved Efficiency of Organic Photovoltaic Cells by Incorporation of AuAg-Alloyed Nanoprisms

We successfully synthesized AuAg-alloyed nanoprisms (AuAgNPrisms) through the seed mediated and galvanic replacement approaches. By introducing the synthesized AuAgNPrisms at the buffer/active interface with an optimal concentration, we increased the power conversion efficiency of PTB7:PC70BM-based organic photovoltaic cells from 6.58% to 7.11%, the current density from 13.36 to 15.01 mA/cm2, corresponding to enhancement factors of 8.1% and 12.4%, respectively. According to our systematical study, we concluded that the incorporation of AuAgNPrisms not only increases light absorption in the active layer over a broad wavelength range but improves the exciton dissociation rate at the interface between PTB7 and PC70BM. With the incorporation of AuAgNPrisms, although the increase in the leakage current is observed, the carrier mobility is also improved apparently, yielding that the reduction in the fill factor is negligible. This work could contribute to the development of high efficiency and low cost organic solar cells.

Influence of solvent treatment with fluoro compounds on the properties of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) polymer as a hole transport layer in polymer solar cells

We prepared high conducting poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) by solvent additives for using as a hole transport layer (HTL) in polymer solar cells (PSCs). PEDOT:PSS films treated with fluoro compounds of hexafluoroacetone (HFA) and hexafluoroisoproponal (HFIPA) with various concentrations show a significant enhancement in electrical conductivity without compromising optical transparency. The conductivity increased from 0.2 to 1053 and 746 S/cm after 4 vol. % HFA and 6 vol. % HFIPA treatments, respectively. The high performance of the PEDOT:PSS layer is attributed to preferential phase segregation of PEDOT:PSS with HFA and HFIPA solvent mixture treatment methods. The improved performance of PSC was dependent on the structure of organic solvents and the concentration of fluoro compounds in PEDOT:PSS solution. Using these optimized layers, conjugated PSCs with a poly[[9-(1-octylnonyl)-9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5 thiophenediyl] polymer:[6,6]-phenyl-C71-butyric acid methyl esters (PCDTBT:PC 71 BM ) bulk heterojunction have been produced. The high power conversion efficiency (PCE) of 4.10% and 3.98% were observed for PEDOT:PSS films treated with 4 vol. % HFA and 6 vol. % HFIPA treatments, respectively. The obtained results show that PEDOT:PSS optimized with HFA and HFIPA organic solvents can be a very promising candidate for transparent anode buffer layer in the low cost organic solar cell devices.

Annealing-free solution-processed tungsten oxide for inverted organic solar cells

Solution processing is mandatory to continue the development of large scale and low cost organic solar cells. Tungsten oxide (WO3) has shown good performance when used as a hole transporting layer in organic solar cells. Here this oxide has been deposited by a sol–gel technique on top of the active layer in an inverted structure device. This layer has been characterised by XPS and UPS to understand the effect of the stoichiometry and of the energy levels on the device performance. In the optimised structure, an average power conversion efficiency (PCE) of 3.5% has been achieved, which is comparable to devices with vacuum deposited transition metal oxide using poly(3-hexylthiophene):[6,6]-phenyl-C61 butyric acid methyl ester (P3HT:PCBM) as an active layer. Moreover in our study no annealing is needed after the deposition of the sol–gel processed oxide, which is really promising for the development of industrial roll-to-roll production on flexible substrates.

Conjugated polymer based on oligobenzo[c]thiophene with low-lying HOMO energy level as potential donor for bulk heterojunction solar cells

Abstract After the discovery of photoinduced charge transfer in conjugated polymers, organic photovoltaic solar cells have been extensively studied due to many advantages that include flexibility and low-cost. In this context, we have synthesized a new class of conjugated polymer, poly(2-(4-{1-cyano-2-[5-(3-thiophen-2-yl-benzo[c]thiophen-1-yl)-thiophen-2-yl]-vinyl}-2,5-bis-hexyloxy-phenyl)-but-2-enenitrile) (CN-PTBTBPB) for the fabrication of low cost organic solar cells. The electron donor properties of CN-PTBTBPB polymer was incorporated by means of facile Knoevenagel condensation process followed by a chemical oxidative polymerization method using oligo-5-(1-benzo[c]thiophen-3-yl)thiophene-2-carboxaldehyde with 1,4-bis(cyanomethyl) benzene linkages. The polymer was characterized by 1 H NMR and GPC techniques. The electronic and structural properties of the polymer were evaluated by UV–vis spectroscopy, fluorescence spectroscopy, and thermo gravimetric analysis. In order to establish the energy diagram of the prepared polymer, the energy gap between HOMO–LUMO was evaluated using electrochemical measurements and Density Functional Theory (DFT). The resulting CN-PTBTBPB polymer was experimentally found to possess low-lying HOMO (about −5.84 eV) and high-lying LUMO (about −3.87 eV) energy levels. This polymer exhibited a relatively wide optical band gap of ~1.95 eV in the solid state. Using this polymer, organic photovoltaic cells were fabricated in open air of type ITO/PEDOT:PSS/CN-PTBTBPB:PCBM/Al showed promising photovoltaic properties.

All solution processing of ITO-free organic solar cell modules directly on barrier foil

In this study, we demonstrate fully solution processed semi-transparent silver electrodes on flexible substrates having a sheet resistance as low as 5Ω/□ and transmittance of ∼30% at 550nm. We demonstrate the use of this electrode as a substitute for ITO in an inverted organic solar cell (OSC) with the layer sequence, PET/Ag/ZnO/P3HT:PCBM/PEDOT:PSS/Ag where illumination is achieved through the first Ag layer. Power conversion efficiency of up to 1.6% under 1 sun illumination (100mWcm−2 and AM1.5G) is achieved for small area (1cm2) test devices. We further demonstrate scalability of the semi-transparent Ag electrode fabrication in a roll-to-roll (R2R) process using slot-die coating. This electrode is further utilized in R2R processing of large area modules (active area 35.5cm2) where all layers in the modules are R2R processed with solution-based materials in ambient conditions without any use of vacuum steps. We further demonstrate the possibility of using barrier foil as the substrate in the R2R processing of modules. Module performance is evaluated by current–voltage characterization and Light Beam Induced Current (LBIC imaging). Such a semi-transparent Ag electrode incurs very little material and processing cost and is a cost-effective alternative to ITO for low-cost organic solar cells.

Cu-based multilayer transparent electrodes: A low-cost alternative to ITO electrodes in organic solar cells

Copper-based multilayer transparent electrodes (MTEs) consisting of a dielectric-metal-dielectric (DMD) structure are explored as a replacement for indium tin oxide (ITO) electrodes in an effort to realize truly low-cost organic solar cells (OSCs). The outer dielectric is shown to play an important role not only in tuning the optical properties of MTEs but also in improving the electrical characteristics of Cu layers, thus providing both high transmission and low sheet resistance. We demonstrate that devices with the optimized Cu-based MTEs can have power conversion efficiency that is as high as 87% of that of ITO-based conventional cells, despite the absorption by Cu in the visible spectrum.

Solution-Processed LiF for Work Function Tuning in Electrode Bilayers

Although ambient processing is the key to low-cost organic solar cell production, high-vacuum thermal evaporation of LiF is often a limiting step, motivating the exploration of solution processing of LiF as an alternative electrode interlayer. Submonolayer films are realized with the assistance of polymeric micelle reactors that enable LiF particle deposition with controlled nanoscale surface coverage. Scanning Kelvin probe reveals a work function tunable with nanoparticle coverage with higher values than that of bare indium tin oxide (ITO).

ITO-free low-cost organic solar cells with highly conductive poly(3,4 ethylenedioxythiophene): p-toluene sulfonate anodes

Indium tin oxide (ITO)-free organic solar cells were fabricated with highly conductive and transparent tosylate-doped poly(3,4-ethylenedioxythiophene: p-toluene sulfonate) (PEDOT:PTS) anodes of various thicknesses that were prepared by the vapor-phase oxidative polymerization of EDOT using Fe(PTS) 3 as an oxidant. Both solution-processable layers – PEDOT:PSS and photoactive P3HT:PCBM – were spin coated. The anodes transmittance and conductivity varied with thickness. Power conversion efficiency was maximized at 1.4%. The ITO-free organic solar cells photovoltaic characteristics are qualitatively compared with those of ITO-based organic solar cells to explore the possibility of replacing costly, vacuum-deposited ITO with highly conductive, patterned polymer films fabricated by inexpensive vapor-phase polymerization.

Atmospheric Plasma Treatment of Flexible IZO Electrode Grown on PET Substrate for Flexible Organic Solar Cells

The atmospheric plasma (AP) surface treatment of a flexible indium zinc oxide (IZO) electrode grown on a poly(ethylene terephthalate) (PET) substrate was investigated as an alternative to oxygen vacuum plasma treatment for low cost organic solar cells. In this study, the surface properties of the flexible IZO electrode were modified by a simple AP treatment without changing their sheet resistance and optical transmittance. X-ray photoemission spectroscopy showed that the atmospheric air plasma treatment led to a decrease in the carbon content and an increase in the oxygen content at the surface of the flexible IZO electrode, indicating that the organic contamination on the flexible IZO electrode was effectively removed by the AP treatment.

First solar cells based on CdTe nanoparticle/MEH-PPV composites

Hybrid bulk heterojunction composites are promising material for low-cost organic solar cells. Fundamental measurements with CdTe nanocrystal/MEH-PPV poly [2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] composites and the first realization of a solar cell based on this material are presented. Optical and electrochemical properties are discussed as well as the current voltage characteristic of the resulting cell. It was found, that CdTe nanocrystal/MEH-PPV composites are well suited for an organic solar cell, even though the technological realization needs to be improved.