Bulk Heterojunction Polymer Solar Cells Research Articles

Facile Synthesis of Dithienobenzothiadiazoles and D18-Cl Polymer via Na2S-Mediated Rapid Thiophene-Annulations for Organic Solar Cells.

We present a novel synthetic route for the rapid construction of dithieno[3',2':3,4;2'',3'':5,6]benzo[1,2-c][1,2,5]thiadiazoles via Na2S-promoted thiophene annulation. This method facilitated the synthesis of D18-Cl polymer, known for its efficacy as a polymer donor in bulk-heterojunction polymer solar cells. Starting from commercially available 4,7-dihalo-5,6-difluorobenzo[c][1,2,5]thiadiazole, various 4,7-dialkynylated compounds were obtained through Sonogashira reaction conditions. Subsequent Na2S-promoted thiophene annulations yielded DTBT and its derivatives in excellent yields within 10 minutes. DTBT was then utilized as a precursor for the concise synthesis of D18-Cl, benefiting from reduced synthetic steps, mild reaction conditions, decreased complexity, and high overall yields. In another route, a space group-bridged DTBT was directly constructed via Na2S-promoted thiophene annulations and converted into D18-Cl through a couple of steps. This developed protocol offers a straightforward and reliable synthetic tool, conducive to reducing complexities in the production of DTBT-based organic electronic materials, thereby advancing the potential commercialization of organic solar cells.

Electrochemically Engineered Lanthanum Nickelate as a Promising Transparent Hole-Transport Layer for Bulk Heterojunction Polymer Solar Cells: An Experimental and DFT Study

Electrochemically Engineered Lanthanum Nickelate as a Promising Transparent Hole-Transport Layer for Bulk Heterojunction Polymer Solar Cells: An Experimental and DFT Study

Metal oxide-embedded carbon-based materials for polymer solar cells and X-ray detectors.

This study examines the effects of hybrid nanoparticles made of NiO@rGO (reduced graphene oxide) and NiO@CNT (carbon nanotubes) on PCDTBT and PCBM active layers in glass/ITO/HTL/active-layer/LiF/Al structured bulk heterojunction (BHJ) polymer solar cells (PSCs) and X-ray photodetectors. These hybrid nanoparticles were used to create BHJ solar cells and photodetectors, and microscopic research was conducted to determine how they affect the structure of the devices. The findings show that compared to conventional matrices, the active layers with NiO@rGO and NiO@CNT incorporation have increased the charge carrier capacities and exciton dissociation properties. In order to assess their impact on the characteristics of charge transport, various weight ratios of these hybrid nanoparticles dispersed in polymer junctions are being investigated. Notably, compared to the pure PCDTBT:PCBM active layer (power conversion efficiency (PCE) = 4.35%), the NiO@CNT device has the highest PCE = 6.42% which, among the tested configurations, demonstrates its superior performance in converting sunlight into electricity. Among the tested X-ray detector materials, "NiO@CNT" achieves the best performance with a sensitivity of 1.92 mA Gy-1 cm-2. Through improved interfacial behaviors and effective charge transport, this work highlights the potential of these cutting-edge hybrid nanoparticles to enhance the performance of organic electronic devices.

Effect of diazine isomers on photovoltaic properties of simple and efficient wide band gap polymer donor materials

In this paper, we designed and synthesized six new wide band gap donor-acceptor (D-A) copolymers, PZ2-PZ7, with diazine isomers (pyrazine, pyridazine, pyrimidine) as the A unit and alkylthiophene- or alkylthiothienyl-substituted BDT as the D unit. The effect of diazine isomeric A units and side-chain substituents on molecular structure, optoelectronic properties and photovoltaic performances of the resulting D-A copolymers were investigated in details. Six low-cost polymers were easily obtained by minimal reaction steps and cheap raw materials. All the polymers exhibited wide band gaps (WBGs) (>1.9 eV) and deep-lying HOMO energy levels (<−5.48 eV), which is convenient for paring with low band gap nonfullerene acceptors (NFAs). Theoretical simulation calculation indicates that diazine isomeric A unit has great impact on the planarity of polymer backbone. Bulk heterojunction polymer solar cells (PSCs) were fabricated with these polymers as donor materials and representative NFAs (Y6 and ITIC) as acceptor materials. After optimization, pyrazine-based polymers PZ2 and PZ3 exhibited higher PCEs than those of pyridazine- and pyrimidine-based ones (PZ4-PZ7) regardless of the acceptors. Finally, the PZ2:Y6-based PSC achieved the highest power conversion efficiency (PCE) up to 11.21 %, which could be attributed to more balanced carrier mobility, increased charge dissociation probability, reduced charge recombination, and superior active layer morphology. This work suggests that diazine-based WBG polymers, especially for pyrazine, would become as very promising donor candidates for constructing low-cost and efficient NFA-based PSCs.

Spatial Balance of Photogenerated Charge Carriers in Active Layers of Polymer Solar Cells.

Bulk heterojunction polymer solar cells (PSCs) blended with non-fullerene-type acceptors (NFAs) possess good solar power conversion efficiency and compatibility with flexible electronics, rendering them good candidates for mobile photovoltaic applications. However, their internal absorption performance and mechanism are yet to be fully elucidated because of their complicated interference effect caused by their multilayer device structure. The transfer matrix method (TMM) is ideal for analyzing complex optical electric fields by considering multilayer interference effects. In this study, an active layer (AL) thickness-dependent TMM is used to obtain accurate information on the photon-capturing mechanisms of NFA-based PSCs for comparison with experimental results. Devices with AL thicknesses of 40-350 nm were prepared, and the AL-thickness-dependent device parameters with incident photon-to-current efficiency spectra were compared with the calculated internal absorption spectra of the TMM. The spectrally and spatially resolved spectra as a function of the AL thickness and excitation wavelength revealed that the power conversion efficiency of the NFA-blended PSC decreased with the increasing AL thickness after reaching a maximum of ~100 nm; by contrast, the internal absorption efficiency showed the opposite trend. Furthermore, the TMM spectra indicated that the spatial distribution of the photogenerated charge carriers became significantly imbalanced as the AL thickness increased, implying that the AL-dependent loss stemmed from the discrepancy between the absorption and the extracted charge carriers.

Effect of active layer thickness on the charge recombination and dissociation in bulk heterojunction polymer solar cells under open circuit conditions

Bulk heterojunction organic photovoltaic cells (OPVs), which are based on anthracene-containing poly (p-phenylene-ethynylene)-alt-poly (p-phenylene-vinylene) (PPE-PPV) polymer denoted (AnE-PVstat) and phenyl C60 butyric acid methyl ester (PCBM). The active layer thickness was varied from 100 nm to 300 nm. The solar cell parameters and magnetoconductance (MC) effect were analyzed, and the results showed a positive MC effect (+MC) for active layer thicknesses of 100 nm, 150 nm, and 200 nm, while a negative MC effect (-MC) was observed for thicknesses of 250 nm and 300 nm. The Power conversion efficiency (PCE) of 4 ℅ was achieved for an active layer thickness of 200 nm. The triplet-doublet quenching (TQD) model was used to describe the MC effect, which is influenced by triplet-charge reactions on the current based on density matrix formalism using the Stochastic Liouville Equation. The dissociation and recombination rates of the T-D pairs increased with the thickness for thinner layers (100, 150, 200 nm) while decreased for thicker layers (250 nm and 300 nm).

Parametric extraction and internal analysis of fullerene-based polymer bulk heterojunction solar cell

This paper present device model simulation describing the current-voltage characteristics of polymer/fullerene bulk heterojunction solar cell. In the research paper an organic photovoltaic device with PPV/PCBM [poly (2-methoxy-5-{3’,7’-dimethyloctyloxy}-p-phenylene vinylene) and {6,6}- phenyl C61-butyric acid methyl ester] was simulated via Silvaco TCAD 2-D simulation tool. PCBM acts as acceptor and PPV is donor. The models used to simulate the device were Langevin for recombination, s.binding and a.singlet. Simulation of these type of devices is an vital approach to project and predict the cell performance. Under the illumination of one sun (AM 1.5) the simulated organic cell showed a short circuit current density (JSC) of 28 A/m2, open circuit voltage (VOC) of 0.84 Volt and a fill factor (FF) of 52.51%, the resulting maximum efficiency of the PPV/PCBM organic solar cell is 1.22%.

Trion-charge-transfer state in bulk heterojunction polymer solar cell

Trion-charge-transfer state in bulk heterojunction polymer solar cell

Effects of Water/Alcohol Soluble Cationic Polythiophenes as Cathode Interlayers for Eco‐Friendly Solar Cells

AbstractThree new ionic polythiophene derivatives, soluble in polar solvents, are synthesized with good yields using simple, low‐cost, and straightforward procedures. They are investigated as interfacial cationic conjugated polyelectrolyte (CPE) layers for halogen‐free bulk heterojunction polymeric solar cells, based on a water‐soluble electron‐donor polymer (poly[3‐(6‐diethanolaminohexyl)thiophene]) and a water‐soluble electron‐acceptor fullerene derivative (malonodiserinolamide fullerene). The simple insertion of the CPE interlayer between the active layer and the aluminum cathode dramatically increases the power conversion efficiency of the final device up to nearly 5%, resulting from a decrease of the electrode work function, improved electron extraction, and optimization of the morphology of the layers. The obtained results demonstrate that the incorporation of CPE layer is a powerful and convenient methodology for the development of highly efficient and eco‐friendly processable polymeric solar cells.

Unraveling the device performance differences between bulk-heterojunction and single-component polymer solar cells

A new conjugated-block copolymer PBDB-YTCl-2 was synthesized. The photovoltaic performance, morphological characteristics and physical mechanisms of PBDB-YTCl-2 were compared with those of the bulk-heterojunction PBDB-T:PYCl-2 system.

Electrochemical deposition of NiO bunsenite nanostructures with different morphologies as the hole transport layer in polymer solar cells

• Electrodeposition of p-type nickel oxide (NiO) using anodic potentiostatic and cyclic voltammetry. • Applying both NiO as the hole transport layer (HTL) in the fabrication of polymer solar cells. • NiO synthesized by the anodic potentiostatic exhibited the best features as the HTL. • The best PSC showed J SC , V OC , FF , and PCE of 10.95 mA/cm 2 , 0.64 V, 0.60 and 4.21%, respectively. Hole transport layers (HTLs) are one of the most important components of bulk heterojunction polymer solar cells (BHJ PSCs), having functions of optimizing interface, adjusting the energy match, and helping obtain higher PCE. Inorganic p-type semiconductors are alternative HTLs due to their chemical stability, high mobility, high transparency, and applicable valence band (VB) energy level. In this work, interlayer engineering in BHJ PSC was performed using solution-processed p-type nickel oxide (NiO) as the HTL. NiO nanostructures were synthesized by anodic potentiostatic and cyclic voltammetry (CV) electrodeposition methods. Simple adjustment of the applied potential regime and electrodeposition parameters led to considerable structural and electrochemical changes in the resulting NiO. Eventually, the best sample was selected in terms of suitable surface conductivity, high optical transparency, and appropriate energy levels. NiO nanostructures with FCC crystal structure synthesized by anodic potentiostatic electrodeposition showed conductivity of 0.038 mS.cm -1 and charge mobility of 2.01 cm 2 .V -1 s -1 , respectively, about 30.2% and 24.8% higher than the NiO synthesized by CV. The anodic potentiostatic electrodeposition method increased the photovoltaic performance of the PSCs by 43% compared to the CV method. The average power conversion efficiencies for the anodic potentiostatic and CV methods were 2.95% and 4.21%, respectively. The PCE of these cells was about 13% and 62% higher than that considered for the reference device prepared based on the PEDOT:PSS HTL.

Electron Transport Layer Optimization for Efficient PTB7:PC70BM Bulk-Heterojunction Solar Cells

Bulk-heterojunction (BHJ) polymer solar cells have received a great deal of attention mainly due to the possibility of higher power conversion efficiency for photovoltaic applications. Therefore, in this study, relatively novel polymer BHJ solar cells are proposed (ITO/ETL/PTB7:PC70BM/PEDOT:PSS/Au) with various electron transport layers (ETL) such as zinc oxysulfide (Zn(O,S)), zinc selenide (ZnSe), and poly[(9,9-bis(3′-((N,N-dimethyl)-N-ethylammonium)-propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] dibromide (PFN-Br). Here, each ETL material is selected based on the energy bandgap compatibility with ITO as well as the PTB7:PC70BM active layer and is based on other physical properties, which are generally required for efficient photovoltaic responses. Each proposed device is comprehensively optimized and then photovoltaic responses are simulated and compared using the software SCAPS-1D. It was observed that the ITO/Zn(O,S)/PTB7:PC70BM/PEDOT:PSS/Au device offered the highest power-conversion efficiency of up to 17.15% with an open-circuit voltage of 0.85 volts, a short-circuit current of 28.23 mA/cm2, and a fill factor of 70.69%.

A New Dibenzoquinoxalineimide-Based Wide-Bandgap Polymer Donor for Polymer Solar Cells.

The molecular design of a wide-bandgap polymer donor is critical to achieve high-performance organic photovoltaic devices. Herein, a new dibenzo-fused quinoxalineimide (BPQI) is successfully synthesized as an electron-deficient building block to construct donor–acceptor (D–A)-type polymers, namely P(BPQI-BDT) and P(BPQI-BDTT), using benzodithiophene and its derivative, which bears different side chains, as the copolymerization units. These two polymers are used as a donor, and the narrow bandgap (2,20-((2Z,20Z)-((12,13-bis(2-ethylhexyl)-3,9-diundecyl-12,13-dihydro-[1,2,5]thiadiazolo [3,4-e]thieno[2,″30′:4′,50]thieno[20,30:4,5]pyrrolo[3,2g]thieno[20,30:4,5]thieno[3,2-b]indole-2,10 diyl)bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile) Y6 is used as an acceptor to fabricate bulk heterojunction polymer solar cell devices. Y6, as a non-fullerene receptor (NFA), has excellent electrochemical and optical properties, as well as a high efficiency of over 18%. The device, based on P(BPQI-BDTT):Y6, showed power conversion efficiencies (PCEs) of 6.31% with a JSC of 17.09 mA cm−2, an open-circuit voltage (VOC) of 0.82 V, and an FF of 44.78%. This study demonstrates that dibenzo-fused quinoxalineimide is a promising building block for developing wide-bandgap polymer donors.

Side‐chain engineering of regioregular copolymers for high‐performance polymer solar cells processed with nonhalogenated solvents

AbstractConjugated polymers for bulk heterojunction polymer solar cells (BHJ PSCs) should be processed with nonhalogenated solvents because of environmental concerns. Here, we report novel regioregular copolymers for high‐performance PSCs processed with nonhalogenated solvents. The regioregular copolymers (i.e., rr‐PfBT2f4T‐2OD and rr‐PfBT2f4T‐2DT) consist of 3″,4′‐difluoro‐2,2′:5′,2″:5″,2‴‐quaterthiophene (2f4T) with different side chains (2‐octadodecyl (OD) and 2‐decyltetradecyl (DT)) and 5‐fluorobenzo[c][1,2,5]thiadiazole (fBT). The regioregular copolymers with controlled fBT orientation show high solubility in nonhalogenated solvents. Both regioregular copolymers possess suitable energy levels, leading to sufficient energy offsets with a nonfullerene acceptor, BTP‐eC11. An rr‐PfBT2f4T‐2DT:BTP‐eC11‐blended film exhibited predominant face‐on orientation compared to the rr‐PfBT2f4T‐2OD:BTP‐eC11‐blended film. In addition, the rr‐PfBT2f4T‐2DT:BTP‐eC11‐blended film showed much more balanced hole/electron mobility (μh/μe ~ 4.73) than rr‐PfBT2f4T‐2OD:BTP‐eC11‐blended film (μh/μe ~ 45.86). Therefore, rr‐PfBT2f4T‐2DT:BTP‐eC11‐based PSCs, processed with 1,2,4‐trimethylbenzene, showed a power conversion efficiency of 13.21% which is 60% higher than rr‐PfBT2f4T‐2OD:BTP‐eC11‐based PSCs.

Plasmonic Effects of Au@Ag Nanoparticles in Buffer and Active Layers of Polymer Solar Cells for Efficiency Enhancement.

Embedding nanoparticles (NPs) in the buffer layer of bulk heterojunction polymer solar cells (BHJ PSCs) excites the surface plasmonic polaritons and enhances the pathlength of the light in the solar cells. On the other hand, embedding NPs in the active layer significantly improves absorption and increases the production of electron-hole (e-h) pairs in BHJ PSCs. Increasing the volume ratio of NPs embedded in BHJ PSCs enables the direct interfacing of the NPs with the active layer, which then serves as a charge recombination center. Therefore, this study integrates the aforementioned phenomena by exploiting the effects of embedding plasmonic Au@Ag NPs in the buffer and active layers of PSC and then determining the optimum volume ratio of Au@Ag NPs. The results show the absorption is increased across the 350–750 nm wavelength region, and the PCE of the device with embedded Au@Ag in two locations is enhanced from 2.50 to 4.24%, which implies a 69.6% improvement in the PCE in comparison to the reference cell. This improvement is contributed by the combined localized surface plasmon resonance (LSPR) effects of multi-positional Au@Ag NPs, spiky durian-shaped morphology of Au@Ag NPs, and optimized volume ratio of Au@Ag NPs embedded in the PEDOT: PSS and PTB7:PC71BM layers.

Thermal imaging and deep optical and electrochemical study of C70 fullerene derivatives with thiophene, pyrrolidine or indene moieties along with electropolymerization with thiophene substituted imine: Blends with P3HT and PTB7

Three C70 fullerene derivatives, namely, C70-BTB and C70-MTB with thiophene or C70-MTP thiophene and pyrrolidyne moieties were synthesized and compared with synthesized C70-IPH containing indene moieties. Moreover, C70-BTB was compared with C60-BTB to analyse in deep the influence of fullerene football and rugby balls on the selected opto-electrical properties of new fullerene derivatives. All fullerene derivatives were characterized theoretically by using both time-dependent and independent density functional theory with the Perdew-Burke-Ernzerhof and Becke-Lee, W. Yang, R.G. Parr. The energy levels of the highest occupied molecular orbitals (HOMOs) and the lowest unoccupied molecular orbitals (LUMOs) were calculated and compared with corresponding values determined experimentally by cyclic voltammetry (CV). It was found that the LUMOHOMO energy gaps determined by the DFT/B3LYP/6–31G(d) method agree very precisely with the corresponding values obtained in the CV experiments. For the first time a possibility of electropolymeryzation of C60-MTB C70-BTB, C70-MTB and C70-MTP with (E)-1-([2,2′:5′,2′'-terthiophen]-5-yl)-N-{4-[4-(4-fluorophenyl)-1,3-thiazol-2-yl]phenyl}methanimine (PV-BLJ-SC14) was shown. All fullerene derivatives and blends with poly(3-hexylthiophene-2,5-diyl) and poly(4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl-alt-3-fluoro-2-[(2-ethylhexyl) carbonyl]thieno[3,4-b]thiophene-4,6-diyl) were investigated in deep by UV–Vis spectroscopy in the solution and as the solid layers together with photoluminescence spectra. Structural defects of created layers based on new fullerene derivatives were studied by atomic force microscopy and thermal imaging. To summarize, the investigated fullerene derivatives present much better electrical properties than widely used PC70BM. Moreover, the indene and pyrrolidine modifications demonstrated the best stability (thermally and at passing current) and electrical performance for all tested modifications. Additionally, a possible molecule rearrangement was observed resulting in improvement of electric conductivity through the layer. Finally, simple bulk-heterojunction polymer solar cells were constructed based on new fullerene derivatives as acceptors.

Purification of nitrogen-doped graphene quantum dots and its application in polymer solar cells

Nitrogen-doped graphene quantum dots (N-GQDs) have potential application in photovoltaic devices because of their adjustable bandgap and remarkable dispersion in amphiphilic systems. In this study, N-GQDs were synthesized and purified, and changes in their optical properties before and after purification were compared. The introduction of the N-GQDs into the ZnO electron transport layer (ETL) of a bulk heterojunction polymer solar cell based on PTB7:PC71BM enhanced the power conversion efficiency (PCE) significantly. Purified N-GQDs showed stronger N doping, obvious blue shift of photoluminescence (PL) emission, and improved dispersion in organic system. After chloroform extraction and purification, the N-GQDs derived from citric acid-urea ethanol solution had the least loss and the most prominent optical performance (quantum yield =41.95%). The purified N-GQDs showed longer fluorescence lifetime than that before purification and still showed strong PL performance after compounding with ZnO ETL. N-GQDs modified ZnO ETL layer has stronger light transmittance and lower impedance. The stronger light transmittance is capable of improving the light absorption of the active layer while the lower impedance can promote electron transfer. Both properties are conductive to the PCE.

New wide band gap π-conjugated copolymers based on anthra[1,2-b: 4,3-b': 6,7-c''] trithiophene-8,12-dione for high performance non-fullerene polymer solar cells with an efficiency of 15.07 %

Developing efficient wide-bandgap copolymer donor materials to match with narrow bandgap non-fullerene acceptors is continuously ongoing for polymer solar cells. Herein, two new D-A copolymers are designed and synthesized by embedding the same anthra[1,2-b:4,3-b':6,7-c"] trithiophene-8,12-dione (A3T) acceptor unit and different donor units, i.e., BDTTZ ( P126 ) and BDTTh ( P127 ). These copolymers showed broad absorption from 350 to 680 nm and deeper HOMO energy level. We have used these two copolymers as donors and a narrow bandgap non-fullerene acceptor Y6 to prepare bulk heterojunction polymer solar cells (PSCs). After the optimization, P126 :Y6 and P127 :Y6 attained overall power conversion efficiency of 15.07% and 12.27%, respectively. The higher PCE for the P126 than P127 is associated with the more efficient photon harvesting and photogenerated excitons, balanced charge transport, and low energy loss. Our results may help to design new polymers with a deeper highest occupied molecular orbital level that will be well-matched with non-fullerene acceptors. • We have used the approach of weak donor and strong acceptor approach to design the D-A copolymers. • Two D-A copolymers were designed with same A3T acceptor and different donors, i.e., BDTTZ ( P126 ) and BDTTh (P127 ). • Both the copolymers showed deeper HOMO energy level to achieved high V OC . • P126 :Y6 and P127 :Y6 showed power conversion efficiency of 15.07% and 12.27%, respectively.

Synthesis of D‐A copolymers based on thiadiazole and thiazolothiazole acceptor units and their applications in ternary polymer solar cells

AbstractWe have designed and synthesized two wide bandgap new donor‐acceptor (D‐A) copolymers consisting of the same alkylthiazole‐substituted benzo[1,2‐b;4,5‐b′]dithiophene (BDTTz) donor unit and but different acceptor units, i.e., thiazolo[5,4‐d]thiazole (TTZ) (P122) and 1,3,‐4 thiadiazole (TDz) (P123) and investigated their optical and electrochemical properties. We have employed these copolymers as donor and fullerene (PC71BM) and narrow bandgap non‐fullerene (Y6) as acceptor, to fabricate binary and ternary bulk heterojunction polymer solar cells (PSCs). The overall power conversion efficiency (PCE) of optimized binary bulk heterojunction PSCs based on P122:Y6 and P123:Y6 is 12.60% and 13.16%, respectively. The higher PCE for PSCs based on P123 than P122 counterparts may be associated with the broader absorption profile of the P123 and more charge carrier mobilities than that for the P122 active layer. With the incorporation of small amount of PC71BM into either P122:Y6 or P123:Y6 binary blend, the corresponding ternary PSCs showed an overall PCE of 14.89% and 15.52%, respectively, which is higher than the binary counterparts using either Y6 or PC71BM as acceptor. Incorporating the PC71BM in the binary host blend increases the absorption in the 300–500 nm wavelength region, generating more excitons in the active ternary layer and helping to dissociate the excitons into free charge carriers more effectively. The more appropriate nanoscale phase separation in the active ternary layer than the binary counterpart may be one of the reasons for higher PCE.

Enhancing the Intermolecular Interactions of Ladder-Type Heteroheptacene-Based Nonfullerene Acceptors for Efficient Polymer Solar Cells by Incorporating Asymmetric Side Chains

Enhancing the Intermolecular Interactions of Ladder-Type Heteroheptacene-Based Nonfullerene Acceptors for Efficient Polymer Solar Cells by Incorporating Asymmetric Side Chains