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Ternary polymer solar cells employing two polymers (P2, PTB7-Th) and one non-fullerene small molecule acceptor (Y6) were constructed using a conventional structure. The PTB7-Th, P2 and Y6 exhibit complementary absorption spectra therefore, the ternary blend consists of these three can maximize the photon harvesting efficiency which is advantageous to boost of short circuit current density of polymer solar cell. After the optimization of the weight ratios between the two donors and keeping constant the weight concentration of acceptor and following solvent vapor annealing in THF for 40 s, P2:PTB7-Th: Y6 (0.3:0.7:1.5) based polymer solar cells attained the power conversion efficiency of 15.46%, superior to that for polymer solar cells based on binary active layers i.e., P2:Y6 (12.62%) and PTB7-Th:Y6 (12.84%), respectively. The open-circuit voltage for the P2:PTB7-Th:Y6 is about 0.88 V which is in between the values for P2:Y6 (0.94 V) and PTB7-Th:Y6 (0.85 V), consistent with the different highest occupied molecular orbital energy level for P2 (−5.38 eV) and PTB7-Th (−5.27 eV). The enhancement in the short circuit current may be associated with the broader absorption profile of the ternary active layer relative to binary counterparts while the enhanced value of fill factor may be originated from the balanced charge transport, suppressed recombination, and faster charge extraction.

Three ([Pt]-DPP)n polymers PA, PB, and PC bearing cyanobiphenyl, alkyloxyphenyl, and triphenylene self-assembling groups were synthesized. The optical, electrochemical, photophysical, and solar cel...

In fullerene-free single-junction organic solar cells despite a small interfacial energy offset between the donor and acceptor materials efficient hole transfer occurs, resulting in power conversion efficiencies (PCE) >16%. Here, we demonstrate efficient organic solar cells by tuning of the electronic properties through simple structural modulation of coumarin-based electron donors. The OSCs with C2:BThIND-Cl:Y6 ternary blends exhibit a PCE of 13.54%, with an increased open circuit voltage (VOC) compared to the C1:BThIND-Cl:Y6-based devices (11.27%). Interestingly, an efficient charge transfer is revealed despite a reduced HOMO orbital offset of 0.02–0.04 eV between the C2 donor and BThIND-Cl and Y6 acceptors, resulting in a lower energy loss of 0.45 eV in ternary devices while still maintaining a maximum EQE of ∼80%@820 nm. The work demonstrates the importance of simple coumarin-based donors and their role in performance improvement for fullerene-free ternary OSCs by facilitating charge carrier transport with suppressed recombination.

A new non-fullerene small molecule acceptor (MPU6) containing a diketopyrrolopyrrole (DPP) acceptor unit as the core, connected to dicyanomethylene-3-ethylrhodanine end-capped units via thienylethynylselenophene bridges, has been designed and synthesized and its optical and electrochemical properties have been examined. MPU6 has been used as an acceptor along with a wide bandgap polymer (TDTBTA) as the donor for solution-processed bulk heterojunction polymer solar cells, thus resulting in a power conversion efficiency (PCE) of 13.14%, which is higher than that obtained when PC71BM is used as the acceptor (6.69%). The increase in PCE for the MPU6-based polymer solar cell is due to the increase in both VOC and JSC, while the FF is lower than that for PC71BM. In addition, PC71BM has been used as a second acceptor to form ternary PSCs, thus achieving a PCE of 15.60%, which is significantly higher than those for the binary counterparts. The increase in PCE for ternary PSCs may be linked to better charge transport and energy transfer, which leads to better utilization of excitons and also leads to the enhancement of JSC and FF.

In this work, nickel oxide nanoparticles (NiO NPs) have been synthesized through highly versatile and cost-efficient chemical precipitation process using polyvinylpyrrolidone (PVP) as a surfactant. The X-ray diffraction (XRD), UV–Visible (UV–Vis), Thermogravimetric analysis (TGA), and Fourier transform infrared (FTIR) techniques were employed to characterize the synthesized NiO NPs. The XRD pattern studies revealed that the NiO NPs have a face-centered cubic (FCC) structure and the mean crystallite size of about 7 nm. The optical band gap of 2.88 eV estimated from the tauc plot of thin film UV–vis absorption spectra. FTIR transmission spectra display a prominent band at ∼433 cm−1, which coincides with the bending vibration of Ni–O bond. The prepared NiO NPs retain the prodigious potential as a transparent electrode towards the solar photovoltaic (PV) cell.

An efficient PSCs consisting of a ternary active layer containing a medium bandgap conjugated polymer P and two well-known non-fullerene acceptors i.e. ITIC-m and Y6 was fabricated. An overall Power Conversion Efficiency (PCE) of about 15.13% was achieved, with the optimized ternary active layer consisting of 20 wt% of ITIC-m in acceptors i.e. P:ITIC-m:Y6 (1:0.3:1.2). This value is higher than that for the binary counter parts i.e. 12.10% and 13.16% for P:ITIC-m (1:1.5 w:w) and P:Y6 (1:1.5 w:w). The higher short circuit current density of the ternary active layer PSCs is related to the broader absorption spectra as compared to the binary active layer analogs. The open circuit voltage of this ternary active layer-based PSC is in between the PSCs based on P:ITIC-m and P:Y6, which may be related with the Lowest Unoccupied Molecular Orbital (LUMO) energy levels of both the acceptor and which form the alloy between the two acceptors. The overlapping of the absorption band of Y6 with the photoluminescence of ITIC-m confirm the energy transfer from ITIC-m to Y6, leading to the improvement in short circuit current. The balanced charge transport, the reduced charge recombination and the fast charge extraction in the ternary blend lead to the higher value of FF. Thus, all these combined effects lead to the high value of PCE.

In recent years, tremendous growth has been seen for solution-processed bulk heterojunction solar cells (BHJSCs) using fullerene-free molecular acceptors. Herein, we report the synthesis, characterization of a coumarin-based organic semiconducting molecule C1, and its use in BHJSCs as an electron donor. The compound exhibited an absorption band at 472 nm in chloroform solution with an optical energy gap of 2.33 eV. The HOMO/LUMO energy levels of C1 were found to be ideal for use in BHJSCs. Using PC

For conjugated polymers of interest in photovoltaic applications, control of the bandgap as well as the energy levels of the molecules are of great importance to improve the efficiency and performance of the resulting polymer solar cells. A general tactic for adjusting these properties via modification of the conjugated polymer structure is by using different and chosen molecular groups for copolymerization. This communication presents the synthesis of conjugated donor–acceptor type polymers that have the same benzotrithiophene (BTT) donor and different acceptor units, i.e. DPP and fluoro-carbazole substituted thieno[3,4-b]pyrazine (FCTP) denoted as P(BTT-DPP) (P1) and P(BTT-FCTP) (P2), respectively, and their photovoltaic performance using as donor, and non-fullerene acceptor (PDIF) in the bulk heterojunction active layer. The bandgaps as well as the HOMO and LUMO energy levels are effectively tuned. The P(BTT-FCTPZ) structure exhibits a smaller bandgap as compared to P(BTT-DPP) that results from the lower LUMO energy and higher HOMO energy due to the FCTP unit. Having optimized the active layers, the PSCs that were based on P(BTT-DPP) and P(BTT-FCTPZ gave an overall power conversion efficiency of about 9.77% and 10.97%, respectively, using a wide bandgap PDIF non-fullerene acceptor, and 8.38% and 9.05, respectively, using PC71BM as electron acceptor.

An environmentally compatible organic solar cell (OSC) has potential to build a global clean energy infrastructure for the world. However, much less attention has been focused on the structures sou...

Polymer solar cells (PSCs) based on binary and ternary active layers were built using PBDB-T polymer as donor and two non-fullerene acceptors (MPU2 and MPU3) with different DPP cores and terminal units but different conjugation length. The studied binary PSCs showed PCE (power conversion efficiency) values of 8.22% (PBDB-T:MPU2) and 9.77% (PBDB-T:MPU3). The VOC measured using the MPU3-based acceptor was higher than that obtained using MPU2 – this difference is attributed to a higher LUMO energy level of MPU3. MPU2 and MPU3 present complementary absorptions in the wavelength range where PBDB-T exhibits a poor absorption, thus the combination of these materials offers great potential for the fabrication of ternary PSCs. The solar cell with an optimized ternary layer PBDB-T:MPU2:MPU3 (1:1:1) showed an PCE value of 10.78%, higher than those obtained for the binary devices due to the enhanced of JSC and FF values. And, since the emission of MPU3 partially overlaps with the absorption of MPU2, the transfer of energy from MPU3 to MPU2 can improve the exciton utilization efficiency and achieve enhanced overall power conversion efficiency in this ternary solar cell.

Nanocomposite thin film containing Au nanoparticles in carbon matrix is developed using co-sputtering method in a high vacuum chamber (

Small molecule donor materials, ICT18, ICT19 and ICT20 are synthesized to explore the effect of donor material architecture/backbone length and nature of central donor moiety on their thermal, optical, electronic and photovoltaic properties. Compared to ICT18 (e, 0.83 × 105 mol−1 cm−1), ICT19 (2.26 × 105 mol−1 cm−1) has higher light harvesting ability indicating that higher conjugation length is essential for better exciton generation and is further enhanced by replacing the BDT unit of ICT19 with DTP unit of ICT20 (2.50 × 105 mol−1 cm−1). Thermal stability of these materials is enhanced and their HOMO level is destabilized with an increase in their conjugation length. BHJSCs are fabricated using these materials as donor and PC71BM as acceptors. Under the optimized conditions, BHJSCs with ICT18, ICT19 and ICT20 donors show PCE of 5.69, 6.92 and 8.13%, respectively. ICT19 and ICT20 with large conjugation length and symmetrical A-D1-D2-D1-A architecture show higher hole conductivity over ICT18 with low conjugation length and unsymmetrical D2-D1-A structure. Photo transient experiments are performed to understand the excited state dynamics of the synthesized materials. The enhancement in the PCE is due to higher light harvesting ability of the active layer with efficient and balanced charge transport and effective exciton dissociation at the donor-acceptor interface.

Three small molecules denoted SM1, SM2 and SM3, with the phenothiazine donor moiety connected to benzothiadiazole and 3-ethylrhodanine acceptor units through thiophene π-linkers have been synthesized for use in organic solar cells with PC71BM as electron acceptor. SM1 has a 2-ethylhexyl group at the phenothiazine nitrogen, while SM2 and SM3 have a 2-(2-methoxyethoxy)ethyl group at that N. Opto-electronic and dielectric properties, charge carrier mobilities, morphology of active layers, and photovoltaic properties were investigated in detail. The three molecules have wide absorption bands with high molar absorption coefficients and relatively low HOMO levels (−5.21 to −5.27 eV). Compared with the N-alkylated SM1, both SM2 and SM3 exhibit red-shifts of the long-wavelength absorption band in thin films, and show enhanced crystallinity in thin films with smaller stacking distances, higher hole mobility, and higher dielectric constant. After solvent vapour annealing, the power conversion efficiencies (PCEs) were significantly improved for the solar cell devices, from 1.69 to 3.95% for SM1, 2.78–6.62% for SM2 and 3.22–7.16% for SM3. This increase in PCEs was due to the enhancement in Jsc and FF attributed to the formation of nanoscale domains of donor and acceptor resulting in efficient charge separation, balanced charge transport and suppressed charge recombination. These results demonstrate that use of an oxygen-containing side chain, in conjunction with alkyl side chains for solubility during solar cell processing, is an alternative and effective strategy for achieving high-performance small molecule donor materials.

Low energy ion irradiation is an interesting tool to accomplish the bulk modifications of different materials. The impact of low energy ion bombardment is studied on Cu-C70 nanocomposite thin films prepared by thermal co-deposition technique. A beam of 180 keV Ar ions was used for this purpose which results in a drastic change in structural, optical and electrical properties. It is demonstrated that surface plasmon resonance (SPR) was successfully induced with ion irradiation initially at a fluence of 3 × 1014 ions cm−2 and is observed to be first red shifted and then blue shifted on increasing fluence of ion irradiation. The results of Raman spectroscopy reveal the progressive transformation of fullerene C70 into amorphous carbon with increasing fluence. The I(D)/I(G) ratio is calculated to analyze amorphous carbon and improved ordering of amorphous carbon at higher fluences is observed. TEM images verified the continuous growth of copper nanoparticles subjected to low energy ion irradiation with increasing fluence which is ascribed to the agglomeration of particles as pointed by EDS mapping images. FTIR results show that the destruction of fullerene C70 matrix is initiated at a fluence of 3 × 1014 ions cm−2, which coincides with the appearance of SPR band. The transformation of fullerene into amorphous carbon and the growth of copper nanoparticles was found to be responsible for increase in conductivity with fluences as confirmed by I-V measurements.

Two D–A–D small molecules with a DPP acceptor core and Zn-porphyrin donor with different electron-donating substituents, namely, 2,6-bis(dodecyloxy)phenyl and 5-hexylthieno[3,2-b]thiophen-2-yl at mesopositions, VC4 and VC5, were synthesized, and their optical and electrochemical properties were investigated. The results reveal that both molecules are suitable as donors for organic solar cells (OSCs) in which PC71BM is employed as the acceptor. Overall power conversion efficiencies of 8.05% (Jsc = 13.83 mA/cm2, Voc = 0.91 V, and FF = 0.64) and 8.89% (Jsc = 16.98 mA/cm2, Voc = 0.79 V, and FF = 0.663) were obtained, respectively. The high Voc value for the VC4-based OSC correlates with the deeper HOMO, whereas the high Jsc value for VC5 may be attributed to the extended absorption spectrum toward the longer wavelength region. Moreover, the relatively high FF value for VC5-based OSCs as compared to the VC4 counterparts may be related to the more balanced charge transport in the active layer, reduced charge re...

A new D–π–A–π–D small molecule (VC7) based on a selenophene-flanked diketopyrrolopyrrole core and two Zn-porphyrin peripheral moieties was designed and synthesized. The optical and electrochemical properties of VC7 were investigated and compared with those of VC6, which has the same chemical structure but with thiophene units in the π-bridge rather than selenophene. VC7 exhibited extended absorption spectra in the near infrared region of the solar spectrum and showed improved hole mobility with a high HOMO energy level. After optimization of the active layers, VC7:PC71BM organic solar cells (OSCs) showed a significantly higher power conversion efficiency of 9.24% (JSC = 15.98 mA cm−2, VOC = 0.89 V and FF = 0.66) in comparison to VC6:PC71BM (PCE of 7.27%, JSC = 14.31 mA cm−2, VOC = 0.82 V and FF = 0.62); this result represents a 27% increase in efficiency. Our results show that the higher JSC value for the VC7-based OSC is due to a combination of the more extended absorption profile, higher hole mobility, more balanced charge transport and high exciton dissociation probability.

We synthesized and characterized a series of new random terpolymers composed of two electron-accepting blocks, diketopyrrolopyrrole (DPP) and benzothiadiazolequinoxaline (BTQx), and one electron-donating benzo[1,2-b:4,5-b′]dithiophene (BDT) unit with different molar ratios of the BTQx block to DPP block (25%, 50%, and 75% BTQx). The random terpolymers compositional effects on the physicochemical properties and photovoltaic performances were studied. Different compositions of DPP and BTQx blocks in the conjugated backbone of the terpolymers had a crucial effect on the electrochemical and optical properties of the random terpolymers. These terpolymers were employed as a donor along with PC71BM as an acceptor for solution-processed polymer solar cells. Among all the terpolymers, P13 (BDT–DPP50–BTQx50) with a monomer composition of BTQx and DPP (50 : 50) blocks showed excellent light-collecting ability, high charge-carrier mobility, and a low-lying HOMO energy level. PSCs based on P13 (BDT–DPP50–BTQx50) exhibited a Voc of 0.86 V, a Jsc of 15.74 mA cm−2, and an FF of 0.68, leading to a high PCE of 9.20%, which is higher than that for D–A copolymers, i.e., P11 (7.37%) and P15 (8.11%). These results demonstrate that random terpolymerization is a simple and practical approach for optimization of a conjugated polymer donor for efficient polymer solar cells.

In this work, two new indolo-[3,2-b]-carbazole (ICz) core-based non-fullerene acceptors (ICz-Rd2 and ICz-RdCN2) with an A–π–D–π–A backbone were designed, synthesized, and characterized and the influence of molecular engineering on the terminal end groups on their performance in organic solar cells (OSCs) was systematically examined. The ICz-Rd2 and ICz-RdCN2 acceptors showed strong and wide-ranging absorption profiles from 350–800 nm in solution and film with high molar extinction coefficients of 6.6 × 104 M−1 cm−1 and 1.0 × 105 M−1 cm−1, respectively. These acceptors were employed along with a low band gap D–A conjugated polymer P as a donor for polymer solar cells and, after optimization of the active layers, the P:ICz-Rd2- and P:ICz-RdCN2-based devices offered overall power conversion efficiencies of 7.88% and 9.76%, which are higher than that of their PC71BM-processed counterpart (5.89%). The enhanced power conversion efficiencies for these non-fullerene acceptors may be related to the wide absorption spectra of the active layers and their low voltage loss.

We have designed an A–π–D–π–A small-molecule triad consisting of a bacteriochlorin (BC) donor central core linked with two diketopyrrolopyrrole (DPP) acceptors via ethynyl bridges (BC-DPP-1). BC-DPP-1 has a narrow optical bandgap of 1.38 eV with highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels of −4.93 eV and −3.40 eV, respectively, and it was used as an electron donor along with [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as an acceptor for solution-processed small-molecule organic solar cells. After optimizing the weight ratio between BC-DPP-1 and PC71BM and pyridine as a solvent additive and subsequent solvent vapor annealing using THF, an organic solar cell based on the optimized BC-DPP-1:PC71BM showed an overall power conversion efficiency of 7.48%. Since BC-DPP-1 shows a weak absorption band in the 650–750 nm wavelength region, we used a second small molecule having strong absorption in this spectral region and prepared the ternary active layer BC-DPP-1 : SM : PC71BM, varying the weight ratio between the two donors and keeping the amount of PC71BM constant. The ternary active layer BC-DPP-1 (70% w/w):SM (30% w/w):PC71BM showed the best photovoltaic performance. After the optimization of the ternary active layer (i.e., the solvent additive and subsequent solvent vapor additive), the organic solar cell showed overall power conversion efficiency of 9.88%. The improved power conversion efficiency resulted from the enhancement of Jsc, Voc and FF as compared to the binary counterpart. Since BC is an analog of porphyrins and chlorophylls, these results demonstrate that benefiting from the narrow band gap of BC-DPP-1 (i.e., organic solar cells with light harvesting in the NIR region of the solar spectrum) can be a real improvement. Moreover, the low energy loss (0.48 eV) as compared to the binary counterpart (0.58 eV) also confirms the suppressed recombination in the ternary organic solar cells.

Two small molecules BYG-1 and BYG-2 with fluorene donor and benzothiadiazole acceptor units connected to the terminal naphthamide group via ethyne linker were designed and synthesized.

Organic solar cells (OSCs) that contain small molecules only were prepared with FG1 as the donor, a narrow band gap non-fullerene acceptor MPU4, and a wide band gap PC71BM. The OSCs based on optimi...

The effect of central donor core on the properties of A-π-D-π-A donors, where D is a porphyrin macrocycle, cyclopenta[2,1-b:3,4-b']dithiophene is the π bridge, and A is a dicyanorhodanine terminal unit, was investigated for the fabrication of the organic solar cells (OSCs), along [6,6]-phenyl-C71-butyric acid methyl ester (PC71 BM) as electron acceptor. A new molecule consisting of Ni-porphyrin central donor core (VC9) showed deep HOMO energy level and OSCs based on optimized VC9:PC71 BM realized overall power conversion efficiency (PCE) of 10.66 % [short-circuit current density (JSC )=15.48 mA/cm2 , fill factor (FF)=0.65] with high open circuit voltage (VOC ) of 1.06 V and very low energy loss of 0.49 eV, whereas the Zn-porphyrin analogue VC8:PC71 BM showed PCE of 9.69 % with VOC of 0.89 V, JSC of 16.25 mA/cm2 and FF of 0.67. Although the OSCs based on VC8 showed higher JSC in comparison to VC9, originating from the broader absorption profile of VC8 that led to more exciton generation, the higher value of PCE of VC9 is owing to the higher VOC and reduced energy loss.

International audience; Two polyyne oligomers using the thiophene–(diketopyrrolopyrrole)–thiophene unit, T–DPP–T, and the organometallic synthon trans-Pt(PBu3)2(C[triple bond, length as m-dash]C)2, [Pt], ([L1]–[Pt])m (P1), here used for comparison purposes, and ([L4]–[Pt])m (P4), where L1 and L4 are T–DPP–T and (T–DPP–T)2, respectively, were synthesized by CuI-catalyzed dehydrohalogenation and fully characterized. The optical and electrochemical properties were investigated by UV-visible absorption and cyclic voltammetry, and P4 was found to exhibit a very low band gap. DFT (density functional theory) and TD-DFT (time-dependent DFT) computations were undertaken to address the polymers’ geometry, their electronic structures and calculated HOMO and LUMO energies. The S1 level is best described as a ππ* excited state. P1 and P4 exhibit fluorescence lifetime in ps timescale and the fs-TAS data indicate an ultrafast electron transfer to PC61BM ((1Px* + PC61BM → Px+˙ + (PC61BM)−˙; time scale < 113–128 fs) evidenced by an increased formation of the triplet state upon back electron transfer (Px+˙ + (PC61BM)−˙) → 1,3Px* + PC61BM; x = 1, 4). The timescale of recombination for P4 (P4+˙ + (PC61BM)−˙ → 3P4* + PCBM) is found to be ∼3 ps. The photovoltaic performance of Px was investigated by fabricating the photovoltaic solar cells (PSCs) with conventional device structure ITO/PEDOT:PSS/(P1 or P4):PC71BM/PFN/Al. After solvent vapour annealing with THF, the power conversion efficiencies, PCEs, are 7.36% (P1; Jsc = 12.94 mA cm−2, Voc = 0.92 V, FF = 0.62) and 9.54% (P4; Jsc = 16.24 mA cm−2, Voc = 0.89 V, FF = 0.66). The higher PCE of P4 may be related to the faster extraction and longer charge carrier lifetime for P4 based PSCs as compared to P1.

Gold–fullerene C60 nanocomposite thin films prepared by thermal co-deposition were irradiated by a high energy beam of 120 MeV Ag ions using Pelletron accelerator. Absorption spectra revealed a large and progressive tuning of surface plasmon resonance wavelength when the films were irradiated at higher fluences. This blue shift (~ 119 nm) can be ascribed to the evolution of fullerene into amorphous carbon upon bombardment of high energy ions at higher fluences and causes a shift in refractive index of the matrix. Raman spectra ascertained this transformation with the presence of two bands: D and G band. Ion irradiation also leads to the formation of bigger size Au nanoparticles with well defined spherical shape at higher fluences as confirmed by TEM. XRD results demonstrated decrease in FWHM of diffraction peaks indicating the increase in particle size which is in agreement with the result obtained from TEM analysis.

We report the swift heavy ion irradiation induced tailoring of structural properties of nanocomposite thin films of copper nanoparticles embedded in fullerene matrix. Cu metal nanoparticles with low metal concentration (~ 5 at%) are deposited in fullerene C60 matrix. The thickness of the combined film is about 50 nm as revealed by Rutherford backscattering spectrometry. The absorbance of copper nanoparticles did not exhibit any characteristic plasmon resonance owing to low concentration of metal. The analysis of results of Raman spectroscopy demonstrated the structural transformation of fullerene to amorphous carbon at high fluence of 120 MeV Au ion beam. The formation of structures such as carbon nanowires as a result of irradiation has been revealed by FESEM micrographs. TEM results confirm the formation of small size copper nanoparticles in pristine film and growth of the Cu particles under the effect of swift heavy ions irradiation. I-V characteristics of metal-fullerene nanocomposite thin films give a clear indication that the value of resistance decreases due to effects of increasing fluence of ion irradiation.

Metal-matrix nanocomposites have a diverse range of applications by virtue of their improved properties. However, further improvements in the characteristics of the composites can be made if we are able to tune the properties of a single constituent of the composite. In the present work, Cu-C70 thin films were grown on glass substrate with thermal co-evaporation technique. In order to induce the surface plasmon resonance (SPR) band, the nanocomposite thin films are irradiated with 120 keV N+ ion beam at the fluence ranging from 1 × 1014 to 3 × 1016 ions/cm2. The Rutherford backscattering is used to know the thickness and concentration of the components present in the nanocomposite thin film. TEM is used to show the increase in particle size of Cu nanoparticles with the increase in the irradiation fluence. The surface analysis shows a decrease in the roughness of the film upto a fluence of 3 × 1014 ions/cm2 and then the roughness increases with the increase in fluence. The UV–visible spectrum shows the formation of SPR band at ∼630 nm at the highest fluence of 3 × 1016 ions/cm2, which is ascribed to the increase in the size of the Cu nanoparticles. The FTIR spectrum shows various bonds of copper - fullerene nanocomposite in pristine film. Raman spectroscopic investigations show the transformation of fullerene C70 matrix of Cu-C70 thin film into amorphous carbon matrix at higher fluences. XPS is also performed to show the elemental state of composite material.

Two organic semiconductor molecules, CS01 and MPU3, an electron donor and electron acceptor, respectively, are described for use in organic bulk heterojunction solar cells. The highest occupied molecular orbital (HOMO) energy offset (ΔEHOMO) between these two molecules is as low as 0.29 eV. Moreover, the lowest unoccupied molecular orbital (LUMO) energy offset (ΔELUMO) is as low as 0.14 eV. Nonetheless, the interfacial charge-transfer process upon light excitation is extremely efficient, and solar cells with efficiencies, under normal conditions, as high as 7.81% have been fabricated. Furthermore, the incorporation of PC71BM (another electron acceptor molecule) to fabricate a triple organic heterojunction led to efficiencies close to 10% at 1 sun irradiation conditions. The improvement is due to a better panchromatic harvesting of the sunlight and a better charge balance, which allows the rapid extraction of carriers before they can recombine.

Herein, we report the effect of incorporation of two types of plasmonic nanocomposites, TiO2–Au and TiO2–Ag in different ratios, in the TiO2 photoanode of dye-sensitized solar cells (DSSCs). Electrophoretic deposition technique (EPD) has been utilized for the deposition of these nanocomposite photoanodes. The high-resolution transmission electron microscopy reveals that the nanocomposites, TiO2–Au and TiO2–Ag, have a wide size distribution of Au (5–60 nm) and Ag (20–130 nm) nanoparticles embedded in the TiO2 matrix. The UV–Visible absorption spectra of these nanocomposite films reveal the enhancement in the optical density due to the plasmonic effect. The DSSC based on photoanode consists of plasmonic nanocomposite TiO2–Au:TiO2–Ag (3:1 ratio) showed power conversion efficiency (PCE) of 10.9% which is 187% higher than that pristine TiO2 counterpart. The enhancement in the PCE has been confirmed by the photoluminescence and electro-impedance spectroscopy indicating that both Au and Ag play an important role in enhancing the PCE of DSSCs due to the plasmonic effect.

The increasing need of fullerenes due to its interesting properties makes it a unique molecule of the current research field. The replacement of fullerene C60 by C70 in various applications makes us to feel more intended towards the knowledge of its structural and optical behaviour under various perturbations. In the present study, the stability of fullerenes (C60 and C70) under low energy ion irradiation is investigated. Both C60 and C70 fullerene thin films were grown on glass substrate and bombarded with 2.4 MeV Ar ions at different fluences ranging from 1 × 1013 to 3 × 1016 ions/cm2. The surface morphology and topology of these films were studied by scanning electron microscopy and atomic force microscopy. The microscopic analysis shows the increase in roughness at low fluence and then roughness decreases at high fluences. At the highest fluence, the roughness of both C60 and C70 becomes equal. Various spectroscopic analysis conducted on irradiated fullerene C60 and C70 thin films show that the bandgap decreases with the increase in fluence. In case of C70 bandgap decreases to 1.6 eV which gives more allowed HOMO–LUMO transitions as compared to fullerene C60. This decrease in bandgap tends to increase the conductivity of the fullerene molecule, hence I–V measurements were performed which shows the decrease in the resistivity of both the fullerene thin films. Raman spectrum reveals the transformation of ball shaped fullerenes into amorphous carbon at higher fluences. The different vibrations in the fullerene molecule are also studied by FTIR spectroscopy. These characteristic traits of both the fullerene are studied giving the idea of the local structure and optical behaviour of the molecule as a matrix component in the metal-matrix nanocomposites.

We describe the use of a near IR non-fullerene low molecular weight organic semiconductor molecule, as electron acceptor, in combination with a wide band gap organic semiconductor electron donor, in efficient bulk heterojunction organic solar cells. The electron acceptor is a 2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione-based molecule while the electron donor is a carbazole derivative. These two small molecules have complementary absorption spectra, and, thus, the heterojunction absorbs from 450 to 950 nm. The optimized photoactive layer shows power conversion efficiency of 7.44% under standard measurement conditions with an estimated energy loss as low as 0.55 eV. Identical solar cells, but using fullerene derivative, PC71BM, result in lower efficiency values (PCE = 5.07%) and greater energy losses (0.86 eV). The better performance of the non-fullerene-based small molecule organic solar cells is due to the higher LUMO energy level for the electron acceptor. Moreover, to improve further the efficiency of th...

A conjugated polymer donor containing BODIPY-thiophene dyads in the backbone, P(BdP-EHT), combined with a low bandgap nonfullerene acceptor (SMDPP) consisting of carbazole and diketopyrrolopyrrole units linked with a tetracyanobutadiene acceptor π-linker, was used to design bulk heterojunction polymer solar cells. After the optimization of the donor to acceptor weight ratio and solvent vapor annealing of the P(BdP-EHT):SMDPP active layer, the resulting polymer solar cell showed an overall power conversion efficiency of 9.29%, which is significantly higher than that for the polymer solar cell based on PC71BM (7.41%) processed under identical conditions. This improved power conversion efficiency is attributed to enhanced values of short circuit photocurrent and open circuit voltage, the better light harvesting efficiency of the P(BdP-EHT):SMDPP active layer in the near-infrared region, and the higher Lowest Unoccupied Molecular Orbital (LUMO) energy level of the SMDPP as compared to PC71BM, combined. Moreov...

Metal matrix composites have a diverse range of applications. We have probed local structural modifications taking fullerene C70 as a model matrix material. In this study, thin films of fullerene C70 were grown on polished silicon and quartz substrates by resistive heating of fullerene C70. In order to understand local structural changes, these semi-crystalline films were irradiated with 120 keV N+ ions at different fluences ranging from 1 × 1013 to 3 × 1016 ions.cm−2. Microscopic analysis shows an increase in topological roughness up to a fluence of 1 × 1015 ions.cm−2 and then a decrease. The size of the particles decreases with increase in the fluence. Various spectroscopic analyses conducted on differently irradiated fullerene C70 films show that the bandgap decreases with the increase in the fluence which will increase the conductivity of the irradiated thin films. These results are proved by I-V measurements showing the decrease in the resistivity at higher fluences. Therefore, this characteristic trait makes fullerene C70 to be used as a prominent matrix component in the composites. Raman spectroscopic investigations reveal that C70 is completely transformed into amorphous carbon at a fluence of 3 × 1016 ions.cm−2. Different vibrational modes in FT-IR are also reported in the present work.

The spin-coated thin films of Poly(3-Hexylthiophene) (P3HT) on the glass and Si (double side polished) substrates have been irradiated with 55 MeV Si+4 swift heavy ions (SHI) at fluences in the range from 1 × 1010 to 1 × 1012 ions/cm2. Structural modifications produced by energetic ions are observed by characterization of pristine and irradiated P3HT thin films. Different techniques like high-resolution X-ray diffraction (HR-XRD), micro-Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR) were used to analyze the structural changes in the material. A significant increase in crystallinity and room temperature electrical conductivity of P3HT film has been detected on exposure to the heavy ions. The observed increase in the electrical conductivity with increased fluences is explained in the light of improved ordering of polymer chains after irradiation. Mott's variable range hopping model has been used to explain the conduction mechanism in the material in the temperature range of 230–350 K. The modification in surface properties also observed using AFM analysis and contact angle measurement. It is observed that nature of the P3HT thin films remains hydrophobic after irradiation.

A new A−π–D−π–A small molecule, denoted as MV72, has been designed and synthesized. The molecule comprises a Zn–porphyrin central donor unit and dicyanovinylene-substituted rhodanine (RhCN) end-capping acceptor units linked by bisthienylenevinylene groups as π-conjugated bridges. The optical and electrochemical properties of MV72 have been investigated as an electron donor for solution-processed organic solar cells (OSCs), and the results were compared to those of MV71, which consists of the same molecular backbone but with different rhodanine end-capping acceptor units. The effects of the end-capping terminal units on the absorption spectra, molecular crystallinity, frontier molecular energy levels, charge transport properties, morphology of active layers, and photovoltaic performance have been investigated. The OSCs based on optimized active layers of MV71/PC71BM and MV72/PC71BM (donor and acceptor weight ratios and solvent vapor annealing) deliver overall power conversion efficiencies (PCEs) of 7.61% a...

Two new acceptor–π(donor)–donor–π(donor)-acceptor small molecules SM1 and SM2 with benzodithiophene (BDT) donor core unit linked via phenothiazine (PTZ) donor units with 1,3–indanedione and malonon ...

The synthesis of a new symmetrical A–D–π–A–D–π–A non-fullerene small molecule acceptor MPU3 is reported. MPU3 consists of a diketopyrrolopyrrole (DPP) central acceptor core coupled to terminal dicyanorhodanine acceptors via a thiophene donor and an ethynyl linker. The optical and electrochemical properties of this compound were investigated. MPU3 showed strong absorption in the 600–850 nm range with an optical bandgap of 1.52 eV and the material was used as an acceptor for the fabrication of solution-processed bulk heterojunction organic solar cells using an A–D–π–A–D–π–A small molecule donor (SMD) consisting of a 5,10-dihydroindolo[3,2-b]indole (DINI) central donor core and benzothiadiazole (BT) acceptor units. This donor has a complementary absorption profile to MPU3. The organic solar cell based on an optimized an SMD:MPU3 active layer afforded overall power conversion efficiencies as high as 9.05%, which is higher than that obtained with an organic solar cell using PC71BM as the acceptor (5.80%) fabricated under identical conditions. Interestingly, the energy loss in the organic solar cell based on SMD:MPU3 is very low, 0.54 eV, when compared to its SMD:PC71BM counterpart (1.02 eV). Low energy loss is an essential feature to achieve high PCE values in organic solar cells.

Two zinc porphyrins, 2 and 8, have been synthesized. Porphyrin 8 displays better electronic communication between the dye and the TiO2 electrode. Photophysical measurements and electrochemistry experiments suggest that both porphyrins are very promising sensitizers for dye-sensitized solar cells (DSSCs). It was found that their molecular orbital energy levels favor electron injection and dye regeneration in DSSCs. Solar cells sensitized by 2 and 8 were fabricated, and it was found that they show power conversion efficiencies (PCEs) of 5.27% and 7.13%, respectively. Photovoltaic measurements (J–V curves) together with the incident photon-to-electron conversion efficiency spectra of the two cells reveal that the higher PCE value of the DSSC based on 8 is ascribed to the higher short-circuit current (Jsc), open-circuit voltage (Voc), and dye loading values. Moreover, the larger charge recombination resistance, longer electron lifetime and shorter electron transport time for 8 also confirm the higher value of the Voc and the Jsc and the FF for the DSSC based on 8.

In an effort to improve the short-circuit current and fill factor, organic solar cells have been developed with ternary blending in a single bulk heterojunction active layer. We report here several all small molecule organic solar cells based on ternary bulk heterojunction active layers. These layers consist of two small molecule porphyrin donors (MV71 and MV72), which have the same backbone but different end-capping acceptor units, and PC71BM as the acceptor. The organic solar cells showed overall power conversion efficiencies of 3.21% and 4.03% for the as-cast MV71:PC71BM and MV72:PC71BM binary active layers, respectively. However, the power conversion efficiency of the ternary active layer, i.e., MV71:MV72:PC71BM (0.2 : 0.8 : 2), was 6.72% and this is higher than the two binary active layer counterparts. The enhancement in the PCE of the ternary active layer is mainly related to the improvement in both the short-circuit current and fill factor and is related to the synergistic effect of the good miscibility of the two donors and improved hole transportation due to the slightly deeper highest occupied molecular orbital energy level of MV72 than MV71. The PCE was further improved to 9.44% with an enhanced short-circuit current and fill factor when the ternary active layer was subjected to solvent vapour annealing for 40 seconds. The ternary organic solar cells showed higher values of the incident photon to current conversion efficiency across the entire wavelength region when compared to the binary counterparts. The same donor backbone facilitates miscibility at the molecular level and the different HOMO and LUMO energy levels of the donors enable charge transport in the devices based on the ternary active layers. The increase in the power conversion efficiency after SVA treatment may be attributed to the migration of MV71 from the mixed region to the donor-acceptor (D-A) interfaces, which in turn affects the charge transfer and recombination processes and is confirmed by the impedance spectroscopy and dark current-voltage measurements.

Three ultralow-bandgap D–A copolymers (P0F, P2F and P4F) based on fluorene-substituted thiadiazoloquinoxaline acceptor and BDT donor units were synthesized and characterized. The effect of the number of fluorine atoms substituted in the fluorene side chain on the optical, electrochemical, crystalline and photovoltaic properties of copolymers was compared. The results showed that the optical properties and lowest unoccupied molecular orbital energy levels of the copolymers are almost the same with an increase in fluorine atoms in the side chain, while the highest occupied molecular orbital (HOMO) energy level is shifted downward. P4F and P2F show better light harvesting abilities, higher crystallinities and low-lying HOMO energy levels than those of P0F. These copolymers were used as donors along with PC71BM as an acceptor for the bulk heterojunction polymer solar cells and optimized by adjusting the donor-to-acceptor weight ratios and solvent vapor treatment. Polymer solar cells based on optimized active layers based on P4F and P2F deliver a power conversion efficiency of 8.15% and 6.38%, respectively, which are higher than that of P0F counterpart (5.04%) due to an increase in all photovoltaic parameters, i.e., short circuit current, open circuit voltage and fill factor, and a very low voltage loss of 0.44 eV.

We have used two unsymmetrical small molecules, named phenothiazine 1 and 2 with a D–A–D–π–D configuration, where phenothiazine is used as a central unit, triphenylamine is used as a terminal unit and TCBD and cyclohexa-2,5-diene-1,4-diylidene-expanded TCBD are used as an acceptor between the phenothiazine and triphenylamine units, as a small molecule donor along with PC71BM as an acceptor for solution processed bulk heterojunction solar cells. The variation of acceptors in the phenothiazine derivatives makes an exciting change in the photophysical and electrochemical properties, hole mobility and therefore photovoltaic performance. The optimized device based on phenothiazine 2 exhibited a high power conversion efficiency of 7.35% (Jsc = 11.98 mA cm−2, Voc = 0.99 V and FF = 0.62), while the device based on phenothiazine 1 showed a low PCE of 4.81% (Jsc = 8.73 mA cm−2, Voc = 0.95 V and FF = 0.58) after solvent vapour annealing (SVA) treatment. The higher value of power conversion efficiency of the 2 based devices irrespective of the processing conditions may be related to the broader absorption and lower band gap of 2 as compared to 1. The improvement in the SVA treated active layer may be related to the enhanced crystallinity, molecular ordering and aggregation and shorter π–π stacking distance of the small molecule donors.

Thiophene-containing molecular materials are recognised as efficient substrates in organic photovoltaics. Herein, we have demonstrated the effect of substitution patterns of thiophenes on the electron accepting ability of perylene bisimide derivatives, which in turn dictates the photovoltaic performance. The thiophene units were integrated through α- or β-positions on the 1- or 1,7-bay positions of perylene-bisimide through alkyne spacers in order to modulate the electronic properties of PBI. The target molecules are structurally robust as per electrochemical studies and exhibited broad absorption in the visible region. Better light harvesting ability and favourable LUMO energy levels render these dyads and triads suitable as electron acceptors in organic solar cells. Bulk heterojunction solar cells were constructed from thienyl–PBI (1–4) as acceptors and a polymer P as a donor. α-Linked 1 and 3 showed a PCE of 5.72% and 6.94% with a remarkable energy loss of 0.55 eV and 0.58 eV, respectively whereas, β-linked 2 and 4 showed an overall PCE of 4.93% and 6.06% with an energy loss of 0.52 eV and 0.54 eV, respectively.

Two D1-A-D2-A conjugated terpolymers with same A (fluorinated benzotriazole, fBTz), D2 (dithienosilole, DTS) and different D1 (bis(undecyl)benzo[2,1-b:3,4-b']dithiophene for P1 and didodecyloxy-benzo[1,2-b:4,5-b']dithiophene for P2) were synthesized and their optical and electrochemical properties were investigated. Compared to P1, the P2 with didodecyloxy side chains in benzodithiophene showed strong interchain π-π interaction, more redshifted absorption spectrum and higher molar extinction coefficient. The X-ray diffraction results indicated their excellent crystallinity and molecular stacking features, especially P2 containing didodecyloxy side chains in BDT. These two terpolymers were used as donor along with PC71BM for the fabrication of bulk heterojunction polymer solar cells. After the optimization of active layers, i.e. weight ratios of terpolymer to PC71BM and concentration of solvent additive (DIO) in the host solvent, the resultant polymer solar cells showed overall power conversion efficiency of 6.95% (Jsc = 12.23 mA/cm2, Voc = 0.93 V and FF = 0.61) and 8.14% (Jsc = 14.08 mA/cm2, Voc = 0.85 V and FF = 0.68) for P1 and P2 based bulk heterojunction active layers, respectively. The higher power conversion efficiency of P2 based polymer solar cell than P1 based counterpart, may be attributed to the more exciton dissociation, better nanoscale morphology and higher hole mobility in P2:PC71BM active layer than P1:PC71BM.

Two copolymers having D-A-D-A (P1) and D-A (P2) structures with quinoxaline acceptor unit and dithienosilole donor unit were synthesized and their optical and electrochemical (both experimental and theoretical) properties were investigated. The optical properties showed that these copolymers P1 and P2 exhibit optical bandgaps of 1.54 and 1.62 eV, respectively, with broader absorption profiles extending up to 800 nm and 770 nm, respectively. The electrochemical investigation of these two copolymers indicates that they exhibit suitable highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels for efficient exciton dissociation and high open circuit voltage in the resultant polymer solar cells (PSCs). These copolymers were used as donors along with the PC71BM as acceptor for the fabrication of solution processed bulk heterojunction PSCs. The optimized P1:PC71BM and P2:PC71BM active layers treated with solvent vapor treatment showed overall power conversion efficiency (PCE) of 7.16% and 6.57%, respectively. The higher PCE of P1-based device as compared to P2 might be attributed to higher crystallinity of P1 and good hole mobility resulting more balanced charge transport. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 376–386

We have design and synthesized two similar A-π-D-π-A structured V-shaped small molecular non-fullerene acceptors named as BYG3 and BYG4 for BHJ-OSCs applications. The molecular architecture of BYG3 and BYG4 consists of an electron rich carbazole as central core, benzothiadiazole as π-spacer and finally it is end caped with naphthamide unit via ethyne linker. The major difference among BYG3 and BYG4 non-fullerene acceptors is fluorine atom substitution at benzothiadiazole unit and the effects of fluorine atom on its optical, electrochemical and photovoltaic properties were well discussed. The optoelectronic properties and band gap of BYG3 and BYG4 acceptors were well synchronized to small molecule donor SMD. Therefore, all small molecule BHJ-OSCs device were constructed using BYG3 and BYG4 as acceptors and small molecule (SMD) as donor results power conversion efficiency (PCE) of 8.09% and 8.57% with high open circuit voltages (Voc) of 1.12 V and 1.05 V respectively. Also, BYG4 based OSCs devices were displayed high values of short-circuit current density (Jsc) and fil factor (FF) are higher for than that for BYG3, may be related to the more effective exciton dissociation and charge transfer in the SMD:BYG4 active layer than that for SMD:BYG3 counterpart. However, the larger value of Voc for the BYG3 based OSCs than BYG4 counterpart may be related to the up-shifted LUMO energy level of BYG3.

Herein, we have designed a ternary system comprising of two small molecules (B2 and B3), as donor and a narrow bandgap non-fullerene small molecule acceptor Y6. The chemical structures of B2 and B3 are close to each other but their absorption spectra are complementary with different energy levels. Using these small-molecules, a ternary organic solar cell was fabricated. The presence of B2 in the B3:Y6 blend increases the photon harvesting as well as also forms cascade energy level arrangement which benefits assisting the balancing between the dissociation of excitons into free charge carriers and their subsequent charge transfer between the two donors (B2 and B3) and the acceptor (Y6). Moreover, the photoluminescence spectroscopy analysis has revealed efficient energy transfer from B2 to B3, which resulted in the effective excitons utilization in ternary device. This way, we have been able to achieve over efficiency of about 12.88% with energy loss of 0.54 eV for the ternary device, greater than that for binary devices i.e., 8.73% with energy loss of 0.51 eV and 9.26% with energy loss of 0.61 eV for B2:Y6 and B3:Y6, respectively. This low energy loss is one of the lowest in the fullerene free ternary photovoltaic devices based on all small molecules (donor and acceptors).

A perylenediimide (PDI) tetramer non-fullerene small molecule acceptor consisting of four PDI units linked to tertraphenylethylene (TPhE) central moiety at their β-positions, denoted as TPhEPDI-4 was designed and synthesized. TPhEPDI-4 was combined with polymeric donor PTB7-Th to fabricate the polymer solar cells. TPhEPDI-4 exhibits an absorption profile ranging from 300 to 630 nm, which is complementary with the PTB7-Th, and the blend PTB7-Th: TPhEPDI-4 exhibits the absorption profile from 300 to 830 nm. The optimized solvent vapor annealed bulk heterojunction-based polymer solar cells showed overall power conversion efficiency of about 10.34% (with a high open-circuit voltage of 1.04 V and voltage loss of 0.53 eV), which is higher than that for the as-cast counterpart (6.12%). The improvement in the power conversion efficiency for solvent vapor annealed active layer-based polymer solar cell is originated from higher and balanced charge carrier mobilities suppressed by bimolecular recombination linked with efficient charge transport. The X-ray diffraction confirms the denser and ordered molecular packing after the solvent vapor annealing as well as crystal coherence length in the PTB7-Th: TPhEPDI-4 film.

A bi-functional nanocomposite thin film containing Ag nanoparticles embedded in fullerene C 70 is synthesized by thermal co-evaporation technique. Tuning of plasmonic resonance of Ag-C 70 nanocomposite is obtained by annealing the nanocomposite thin film at different temperatures from 80 to 300 °C for 30 min. The optical and structural properties of nanocomposite thin film with respect to high temperature are studied by UV–visible absorption spectroscopy and X-ray diffraction. Transmission electron microscopy is performed to investigate the temperature dependent size evolution of Ag nanoparticles in fullerene C 70 matrix. Growth of Ag nanoparticles is observed with increasing temperature above 200 °C due to enhanced diffusion of Ag in fullerene C 70 and Ostwald ripening. The optical and structural properties of metal-fullerene nanocomposite is not significantly affected upto a temperature of 150 °C, after that a progressive blue shift of ~ 27 nm in SPR wavelength is observed with increasing temperature. The tuning of SPR is ascribed to the thermal induced structural transformation of fullerene C 70 matrix into amorphous carbon and also to mutual polarization of the particles.

High energy ion irradiation significantly affects the size and shape of nanoparticles in composites. Low concentration metal fraction embedded in fullerene matrix in form of nanocomposites was synthesized by thermal co-evaporation method. Swift heavy ion irradiation was performed with 120 MeV Au ion beam on Cu-C60 nanocomposites at different fluences 1 × 1012, 3 × 1012, 6 × 1012, 1 × 1013 and 3 × 1013 ions/cm2. Absorption spectra demonstrated that absorption intensity of nanocomposite thin film was increased whereas absorption modes of fullerene C60 were diminished with fluence. Rutherford backscattering spectroscopy was also performed to estimate the thickness of the film and atomic metal fraction in matrix and found to be 45 nm and 3%, respectively. Transmission electron microscopy was performed for structural and particle size evaluation of Cu nanoparticles (NPs) in fullerene C60 matrix. A growth of Cu nanoparticles is observed at a fluence of 3 × 1013 ions/cm2 with a bi-modal distribution in fullerene C60. Structural evolution of fullerene C60 matrix with increasing fluence of 120 MeV Au ion beam is studied by Raman spectroscopy which shows the amorphization of matrix (fullerene C60) at lower fluence. The growth of Cu nanoparticles is explained using the phenomena of Ostwald ripening.