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[Display omitted] Organic solar cells have been fabricated using various concentrations of lead sulfide quantum dots. Data from Mott–Schottky analysis revealed intriguing changes in the bulk heterojunction layer of the solar cells that were directly related to the addition of the quantum dots. Notably, the highest power conversion efficiency of 5.15% was achieved with the addition of 0.4 wt% lead sulfide quantum dots. [ABSTRACT FROM AUTHOR]

Organic photodiodes (OPDs) composed of (poly[[4,8-bis[(2-ethyl-hexyl)oxy]benzo[1,2-b:4,5-b0]dithiophene-2,6-diyl][3-fluoro-2-(2-ethylhexy) carbonyl] thieno [3,4-b]thiophennediyl]]) (PTB7) as the donor and o-xylenyl-C60-bisadduct (OXCBA) as an acceptor material were investigated. The concentration of the photoactive film blend ratios of PTB7:OXCBA was varied at 1.00:0.25, 1.00:0.50, 1.00:1.00, and 1.00:1.50. The OPD with the 1.00:1.00 ratio showed the best performance, with rise time and fall time of 310 ms and 445 ms, respectively, much faster than most photoactive films. The detector displayed good photocurrent density, fast photo-response time, and high consistency towards the rapid change of light intensity. The enhanced performance was mainly driven by the improvement in the charge extraction efficiency ascribed to the improvement in the interpenetrating network between the interface of the donor and acceptor. It was found that the photodetector exhibits good photo-responsivity of 118 mA/W with specific detectivity of 6.32 × 109 Jones at a bias voltage of −1 V. [ABSTRACT FROM AUTHOR]

We demonstrate a poly ([4,8-bis[(2-ethylhexyl) oxy]benzo[1,2-b:4,5-b’]dithiophene-2,6-diyl][3-fluoro-2-[(2-et- hylhexyl)carbonyl]thieno[3,4-b] thiophenediyl]) (PTB7) decorated zinc oxide (ZnO) nanorod-based interdigitated metal–semiconductor–metal (MSM) device as ammonia (NH3) sensor at room temperature. The gas sensor response is 66.92% at 20 ppm and 2 V of bias at ambient temperature (~25 °C). The average roughness and the root-mean-square roughness of the hydrothermally synthesized ZnO nanorods (ZnO NRs) were measured as 0.140 and $0.175 ~\mu \text{m}$ , respectively. The device was found sensitive at gas concentration as low as ~2 ppm with a response of 7.12%. At a gas flow rate of 20 ppm and a bias of 2 V, the response and recovery times of the as-fabricated device were measured to be 5 and 30 s, respectively. [ABSTRACT FROM AUTHOR]

Herein, studies on the influence of the cathode metal work function (W) on electric parameters of PEDOT:PSS/PTB7:PC70BM/metal solar cells, especially their power conversion efficiency (PCE) and open‐circuit voltage (Voc), are reported. Along with standard cathode materials, like Al and Ag, 12 more metals and metal bilayers, In, InAl, Al3004 alloy, CaAl, MgAl, ZnAl, Sn, Ti, Au, TiAu, and Ni, are checked. It is found that although the photo‐voltage is generated mainly in the active layer, the W of cathode also affects Voc and the overall efficiency. Voc increases with W and the linear coefficient is about 0.33–0.39. A similar effect is observed for solar cells with P3HT donor material. The electrical and optical properties of the cells with different cathodes just after preparation are investigated and aging measurements are also conducted. The highest PCE is obtained for InAl cathode, 4.9%, which is better than for pure Al cathode. Moreover, long‐time measurements show that the cells with InAl cathode degrade about two times slower than the cells with Al electrode. Photocurrent spectroscopy reveals a blue shift of the solar cell sensitivity spectrum with an increase of W which is probably due to state filling (Burstein–Moss effect). [ABSTRACT FROM AUTHOR]

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%. [ABSTRACT FROM AUTHOR]

Herein, diblock copolymer reverse micelle templating (RMD) is used to control the reaction kinetics of metal halide hybrid perovskites formation to fabricate systems showing dual‐phase emission. Through micelle templating, desired compositions can be engineered which show high phase stability of mixtures of perovskite nanoparticles (NPs) through micellar shielding and stabilizing of the cage structure. In addition, Stokes shift of around 150 nm, one of the largest reported for perovskite systems, can be obtained with careful control over synthesis kinetics. Using an unconventional approach, that is, mixing methylammonium iodide (MAI) and lead bromide PbBr2, systems consisting of both green‐ and red‐emitting NPs are fabricated by a two‐step reaction process using RMD. By obtaining two stable phases in a single solution, the NP system can absorb in the ultraviolet region and emit in the red region, making them excellent candidates for downconversion to improve solar cells efficiency, as shown for two polymer active layers in organic bulk heretojunction solar cells (OPVs). Exploiting the phase stabilizing effect of the micelles, the reaction kinetics of perovskite formation can be tuned for various halide substitutions, opening up new avenues for coexisting perovskite phases for photovoltaic and light‐emitting applications.

We synthetized a new rod-coil block copolymer (BCP) based on the semiconducting polymerpoly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl}) (PTB7) and poly-4-vinylpyridine (P4VP), tailored to produce water-processable nanoparticles (WPNPs) in blend with phenyl-C71-butyric acid methyl ester (PC71BM). The copolymer PTB7-b-P4VP was completely characterized by means of two-dimensional nuclear magnetic resonance (2D-NMR), matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry (MS), size-exclusion chromatography (SEC), and differential scanning calorimetry (DSC) to confirm the molecular structure. The WPNPs were prepared through an adapted miniemulsion approach without any surfactants. Transmission electron microscopy (TEM) images reveal the nano-segregation of two active materials inside the WPNPs. The nanostructures appear spherical with a Janus-like inner morphology. PTB7 segregated to one side of the nanoparticle, while PC71BM segregated to the other side. This morphology was consistent with the value of the surface energy obtained for the two active materials PTB7-b-P4VP and PC71BM. The WPNPs obtained were deposited as an active layer of organic solar cells (OSCs). The films obtained were characterized by UV-Visible Spectroscopy (UV-vis), atomic force microscopy (AFM), and grazing incidence X-ray diffraction (GIXRD). J-V characteristics of the WPNP-based devices were measured by obtaining a power conversion efficiency of 0.85%. Noticeably, the efficiency of the WPNP-based devices was higher than that achieved for the devices fabricated with the PTB7-based BCP dissolved in chlorinated organic solvent. [ABSTRACT FROM AUTHOR]

The present review is mainly focused on the extended analysis of the results obtained from coupled measurement techniques of a thermal imaging camera and chronoamperometry for imines in undoped and doped states. This coupled technique allows to identify the currentvoltage characteristics of thin films based on imine, as well as to assess layer defects in thermal images. Additional analysis of results provides further information regarding sample parameters, such as resistance, conductivity, thermal resistance, and Joule power heat correlated with increasing temperature. As can be concluded from this review, it is possible not only to study material properties at the supramolecular level, but also to tune macroscopic properties of π-conjugated systems. A detailed study of the structurethermoelectrical properties in a series of eight unsymmetrical and symmetrical imines for the field of optoelectronics and photovoltaics has been undertaken. Apart from this molecular engineering, the imines properties were also tuned by supramolecular engineering via protonation with camphorsulfonic acid and by creation of bulk-heterojunction compositions based on 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) and/or [6,6]- phenyl-C71-butyric acid methyl ester, poly(3,4-ethylenedioxythiophene) towards the analysed donor or acceptor ability of imines in the active layer. The use of coupled measurement techniques of a thermal imaging camera and chronoamperometry allows obtaining comprehensive data on thermoelectric properties and defects indicating possible molecule rearrangement within the layer. [ABSTRACT FROM AUTHOR]

This letter reports the fabrication and characterization of a ZnO nanorods / p-type poly[[4,8-bis [(2 ethylhexyl) oxy] benzo [1,2-b:4,5- $\text{b}'$ ]dithiophene-2,6-diyl][3-fluoro-2-[(2ethylhexyl)carbonyl] thieno [3,4-b] thiophenediyl]](PTB7) polymer hybrid heterojunction based high performance ultraviolet-visible (UV-Vis) wideband photodetector. Under a low bias voltage of −1 V, the device shows the responsivities, detectivities and external quantum efficiencies (EQEs) measured at 380 nm (UV) and 640 nm (visible) wavelengths are ~307.18 A/W and ~33.64 A/W; $\sim 1.56\times 10$ 13 Jones and $\sim 1.7\times 10 ^{12}$ Jones; and $\sim 100.23\times 10 ^{3}$ % and $\sim 6.51\times 10$ 3 % respectively. [ABSTRACT FROM AUTHOR]

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%.

Perovskite materials, due to their excellent photovoltaic features, have aroused the researchers′ admiration as a photon‐absorption film for the next‐generation photovoltaics. The interface tailoring of perovskites and hole‐transport layer (HTL) is one of the critical approaches to achieve effective and stabilized perovskite solar cell (PSC). Hence, poly[4,8‐bis[(2‐ethylhexyl)oxy]benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl][3‐fluoro‐2‐[(2 ethylhexyl)carbonyl]thieno[3,4‐b]‐thiophenediyl] (PTB7) as a polymeric organic semiconductors was employed for doping of anti‐solvent solution to modify the perovskite film. Results showed with PTB7 dopant; grain boundaries (GBs) of the perovskites are reduced. It suppressed carriers′ trap centers in the perovskite film and decreased recombination processes within perovskite layers. Besides, the high intrinsic conductivity of PTB7 material assisted charge injection at the perovskites/HTL interfaces and hindered carrier's accumulation. The device with PTB7 showed a more matched energy level and a higher prevention for recombination than the device without PTB7 dopant, which are reasons for the considerable boost in the open‐circuit voltage (VOC) and fill‐factor (FF), giving rise a power conversion efficiency (PCE) of 19.18 % for the champion performing PVs. Most important, the hydrophobic origin of PTB7 leads to superb humidity stability in the device with PTB7 dopant with 85 % of the original performance remaining after more than 800 h storing in air with ∼40 % RH. [ABSTRACT FROM AUTHOR]

Herein, we report the synthesis of nontoxic pyrite iron sulfide (FeS2) nanocrystals (NCs) using a two-pot method. Moreover, we study the influence of these NCs incorporated into the PTB7:PC71BM active layer of bulk-heterojunction ternary organic photovoltaic (OPV) cells. The OPV devices are fabricated with the direct configuration glass/ITO/PEDOT:PSS/PTB7:PC71BM:FeS2/PFN/FM. The Field’s metal (FM) is a eutectic alloy composed of 32.5% Bi, 51% In and 16.5% Sn by weight that melts at 62 °C. It is deposited on the active layer/PFN under atmospheric conditions. Ternary active layers are prepared by adding small amounts of the semiconducting FeS2 NCs at different weight ratios of 0.0, 0.25, 0.5, and 1.0 wt % with respect to the electron donor PTB7. With respect to the reference device (without FeS2), a 21% increase in the power conversion efficiency (PCE) is observed for OPVs with 0.5 wt % FeS2, such that the PCE of the OPVs is enhanced from 5.69 to 6.47%. According to the Kruskal–Wallis and Mann–Whitney statistical tests, all OPV devices follow the same trend.

We synthetized a new rod-coil block copolymer (BCP) based on the semiconducting polymerpoly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl}) (PTB7) and poly-4-vinylpyridine (P4VP), tailored to produce water-processable nanoparticles (WPNPs) in blend with phenyl-C71-butyric acid methyl ester (PC71BM). The copolymer PTB7-b-P4VP was completely characterized by means of two-dimensional nuclear magnetic resonance (2D-NMR), matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry (MS), size-exclusion chromatography (SEC), and differential scanning calorimetry (DSC) to confirm the molecular structure. The WPNPs were prepared through an adapted miniemulsion approach without any surfactants. Transmission electron microscopy (TEM) images reveal the nano-segregation of two active materials inside the WPNPs. The nanostructures appear spherical with a Janus-like inner morphology. PTB7 segregated to one side of the nanoparticle, while PC71BM segregated to the other side. This morphology was consistent with the value of the surface energy obtained for the two active materials PTB7-b-P4VP and PC71BM. The WPNPs obtained were deposited as an active layer of organic solar cells (OSCs). The films obtained were characterized by UV-Visible Spectroscopy (UV-vis), atomic force microscopy (AFM), and grazing incidence X-ray diffraction (GIXRD). J-V characteristics of the WPNP-based devices were measured by obtaining a power conversion efficiency of 0.85%. Noticeably, the efficiency of the WPNP-based devices was higher than that achieved for the devices fabricated with the PTB7-based BCP dissolved in chlorinated organic solvent.

Scanning transmission electron microscopy (STEM) at low energies (≤ 30 keV) in a scanning electron microscope is well suited to distinguish weakly scattering materials with similar materials properties and analyze their microstructure. The capabilities of the technique are illustrated in this work to resolve material domains in PTB7:PC71BM bulk-heterojunctions, which are commonly implemented for light-harvesting in organic solar cells. Bright-field (BF-) and high-angle annular dark-field (HAADF-) STEM contrast of pure PTB7 and PC71BM was first systematically analyzed using a wedge-shaped sample with well-known thickness profile. Monte-Carlo simulations are essential for the assignment of material contrast for materials with only slightly different scattering properties. Different scattering cross-sections were tested in Monte-Carlo simulations with screened Rutherford scattering cross-sections yielding best agreement with the experimental data. The STEM intensity also depends on the local specimen thickness, which can be dealt with by correlative STEM and scanning electron microscopy (SEM) imaging of the same specimen region yielding additional topography information. Correlative STEM/SEM was applied to determine the size of donor (PTB7) and acceptor (PC71BM) domains in PTB7:PC71BM absorber layers that were deposited from solution with different contents of the processing additive 1,8-diiodooctane (DIO). [ABSTRACT FROM AUTHOR]

Primary loss mechanisms in a single junction solar cell are below E g loss and thermalization loss which limits the maximum achievable cell efficiency. In order to overcome the fundamental loss mechanisms called transmission loss due to the mismatch of the solar spectrum with the photoactive layer absorption spectrum, the up-conversion mechanism was adopted to improve the performance of organic photovoltaics. This mechanism was adopted using rare-earth nanoparticle β-NaYF 4 :Yb3+/Er3+ in P3HT and PTB7 conducting polymer-based n-i-p organic photovoltaic device. β-NaYF 4 :Yb3+/Er3+ nanoparticles absorb infrared (IR) photons whose wavelength approximately 980 nm and emit photons in the green wavelength region with the emission intensity maximum occurs at 520 nm and 541 nm. This non-linear optical process (up-conversion mechanism) was used in the polymer solar cell. The polymers used in this study exhibits the absorption range from ~300 nm to 680 nm and 300 nm-800 nm respectively for P3HT and PTB7. Using β-NaYF 4 :Yb3+/Er3+ in polymer solar cell can reduce the transmission loss through harvesting IR photons. In this study, up-conversion nanoparticles (UCNPs) were embedded between the photoactive layer and anode interface to harvest IR light. Presence of these UCNPs assists in visible photons generation process in the vicinity of the photoactive layer which leads to the increased photo collection. Optimum loading of β-NaYF 4 :Yb3+/Er3+ nanoparticles in the device interface for improvement in the photocurrent and efficiency were investigated and correlated with the device optical and electrical processes. The optical process suggests that improvement in photocurrent is a synergistic effect of the up-conversion process and light scattering by β-NaYF 4 :Yb3+/Er3+. The device with UCNPs showed absorbance improvement which suggests that backscattered light at the anode/active layer interface improve the active layer absorption. Detailed investigation of the device properties allows interpreting that the photocurrent improvement is an up-conversion process as well as the scattering. In the optimized up-conversion based device, the photo-current due to up-conversion process and light scattering are of the same order. However, this can vary with respect to photoactive layer absorption properties. Image 1 • Effect of up-conversion mechanism in polymer photovoltaics was studied. • Optical absorption properties due to up-conversion and scattering was studied. • Device short circuit current density is discussed in the detail. • PCE improves with the optimum level of up-conversion in OPV. [ABSTRACT FROM AUTHOR]

Polymer-based organic solar cells are of great interest as they can be produced with low-cost techniques and also have many interesting features such as flexibility, graded transparency, easy integration, and lightness. However, conventional wide bandgap polymers used for the light-absorbing layer significantly affect the power conversion efficiency of organic solar cells because they collect sunlight in a given spectrum range and due to their limited stability. Therefore, in this study, polymers with different bandgaps were used, which could allow for the production of more stable and efficient organic solar cells: P3HT as the wide bandgap polymer, and PTB7 and PCDTBT as low bandgap polymers. These polymers with different bandgaps were combined with PCBM to obtain increased efficiency and optimum photoactive layer in the organic solar cell. The obtained devices were characterized by measuring optical, photoelectrical, and morphological properties. Solar cells using the PTB7 and PCDTBT polymers had more rough surfaces than the reference cell using P3HT. The use of low-bandgap polymers improved Isc significantly, and when combined with P3HT, a higher Voc was obtained. [ABSTRACT FROM AUTHOR]

Abstract In this study, the stability of polymer-based photovoltaic fibers was investigated in ambient and inert atmosphere. Photovoltaic (PV) fibers, similarly produced by using both polymer blend of wide and low bandgap polymers (P3HT: PTB7: PCDTBT) and only wide bandgap (P3HT) polymer with [6,6]-phenyl C61 butyric acid methyl ester (PCBM) in active layer were measured in ambient and in inert environment after dark storage, and then, their photovoltaic performances and stabilities were compared. Maximum power conversion efficiency of 2.01% was obtained from photovoltaic fiber with P3HT: PTB7: PCDTBT polymer blend. When stability results were considered, at end of 7th day, photovoltaic fibers having P3HT: PTB7: PCDTBT:PCBM active layer showed better performance than P3HT: PCBM-based PV fibers. Highlights • Photovoltaic fibers with different bandgaps were produced. • The lifetime of the photovoltaic fibers first time in literature was investigated. • The lifetime of the photovoltaic fibers in different environments was investigated. • Photovoltaic fibers with low bandgap polymers blend has better efficiency. [ABSTRACT FROM AUTHOR]

• We synthesized three imines with triphenylamine or terthiophene core. • We analyse photovoltaic properties in the level of symmetry of imines, presence of DIO, DPE, PFN. • The J-V effects depend on the chemical structure of imine and presence of additives. • Organic solar cells containing PV-BLJ-SC2 imine and PTB7:PC 71 BM:DIO showed the efficiency increased by more than 107 % compared with reference device lack of imine. • We presents a quite effective and cheap method to improve the efficiency of organic solar cells by adopting a ternary approach. In this paper the influence of imine symmetry and triphenylamine moieties presence on photovoltaic properties of bulk heterojunction organic solar cells were analysed in details. Three imines: (E)-N-(4-((4-((E)-(benzo[d]thiazol-2-ylimino)methyl)phenyl)(phenyl)amino)benzylidene)benzo[d]thiazol-2-imine (PV-BLJ-SC1), (E)-N-(4-diphenylamino)benzylidene)benzo[d]thiazol-2-imine (PV-BLJ-SC2) and (N,N'E,N,N'E)-N,N'-([2,2′:5′,2′'-terthiophene]-5,5′'-diylbis(methanylylidene))bis(benzo[d]thiazol-2-imine) (PV-BLJ-SC3) were investigated as donor or acceptor components in binary and ternary active layer. Moreover, the influence of admixture (1,8-diiodooctane or diphenyl ether), and presence of poly[(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9–dioctylfluorene)] as cathode buffer layer on the photovoltaic parameters of the constructed imine-containing solar cells was analysed in details. All the conducted experiments confirmed the possibility of using unsymmetrical imine PV-BLJ-SC2, showing the best results, in organic photovoltaics. The HOMO and LUMO levels of the imines were determined by cyclic voltammetry, showing dependance of on the chemical structure and its symmetry, and for PV-BLJ-SC2 gaved −5.07 eV and −2.23 eV, respectively. In the case of PV-BLJ-SC1 and PV-BLJ-SC2 the electron density of HOMO was mainly located on triphenylamine moieties, while in the case of PV-BLJ-SC3 on thiophene moieties, as it was confirmed by the density functional theory studies. Based on the highest conductivity (9 × 10-8 S/cm2) result for PV-BLJ-SC2, this imine was selected to prepare binary and ternary layers with PTB7 or PTB7:PC 71 BM and thermal imaging studies were performed. Finally, PV-BLJ-SC2 was introduced to the PTB7:PC 71 BM binary system, where a power conversion efficiency as high as 4.17% was achieved after the addition of 1,8-diiodooctane. It gaved better result than the reference sample containing PTB7:PC 71 BM and 1,8-diiodooctane (3.11%). In the case of reference solar cells the addition of 1,8-diiodooctane improved the efficiency of about 22 %, while for solar cells containing also PV-BLJ-SC2 imine the efficiency increased by more than 107 %. Our study presents a quite effective and cheap method to improve the efficiency of organic solar cells by adopting a ternary approach. [ABSTRACT FROM AUTHOR]

Recent studies have shown that molecular aggregation structures in precursor solutions of organic photovoltaic (OPV) polymers have substantial influence on polymer film morphology, exciton and charge carrier transport dynamics, and hence, the resultant device performance. To distinguish photophysical impacts due to increasing π-conjugation from chain lengthening and π–π stacking from single/multi chain aggregation in solution and film, we used oligomers of a well-studied charge transfer polymer PTB7 with different lengths as models to reveal intrinsic photophysical properties of a conjugated segment in the absence of inter-segment aggregation. In comparison with previously studied photophysical properties in polymeric PTB7, we found that oligomer dynamics are dominated by a process of planarization of the conjugated backbone into a quinoidal structure that resembles the self-folded polymer and that, when its emission is isolated, this quinoidal excited state resembling the planar polymer chain exhibits substantial charge transfer character via solvent-dependent emission shifts. Furthermore, the oligomers distinctly lack the long-lived charge separated species characteristic of PTB7, suggesting that the progression from charge transfer character in isolated chains to exciton splitting in neat polymer solution is modulated by the interchain interactions enabled by self-folding.

Abstract We investigate the charge carrier dynamics of inverted organic solar cells (OSCs) based on PffBT4T-2OD: PCBM and PTB7: PCBM – the two leading systems among the OSCs based on polymer-fullerene bulk-heterojunction – to elucidate the origin of their performance difference. Transient absorption spectroscopy (TAS) and photo-electrochemical impedance spectroscopy (photo-EIS) were employed to unravel the photo-physics that govern the cell operation of these two highly efficient bulk heterojunction OSCs. While photo-EIS indicates that the two systems under study exhibit similar behavior in terms of recombination, TAS results reveal that PffBT4T-2OD: PCBM systems not only have higher charge generation rate but also more efficient charge transfer than PTB7: PCBM systems, leading to the power conversion efficiency of PffBT4T-2OD: PCBM-based OSCs (9.16%) that is higher than that of PTB7: PCBM-based OSCs (6.44%). Graphical abstract Image 1 Highlights • Charge carrier dynamics of PffBT4T-2OD: PCBM and PTB7: PCBM OSCs have been compared. • TAS and Photo-EIS measurements along with optical simulation were carried out. • Higher PCE for PffBT4T-2OD: PCBM OSCs is due to better absorption and carrier collection efficiency. [ABSTRACT FROM AUTHOR]

Abstract In this study, two size-controllable silver nanoparticles, decahedral and icosahedron Ag NPs, were embedded into PEDOT:PSS as hybrid hole transporting layer (HTLs) for organic photovoltaic applications. The Ag-decahedral based nanoparticle exhibited rather red-shifted and larger domain size than Ag-icosahedron one. Due to the plasmonic and light harvesting effects of Ag NPs, the power conversion efficiency (PCE) was increased from 5.8% to 6.5 (decahedral-based) and 6.3% (icosahedron-based) in Poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7):[6,6]-Phenyl C71-butyric acid methyl ester (PC 71 BM) based-OPV upon embedding the Ag NPs. External quantum efficiency (EQE) enhancement was also observed due to the plasmonic scattering effect. The atomic force microscope (AFM) images showed the roughed results of the PEDOT:PSS/Ag NPs hybrid HTL films, i.e. better hole collection efficiency. Furthermore, the active layer did not show any aggregation and morphology change after adopting hybrid HTL films into the devices. Graphical abstract Image 1 Highlights • Two size-controllable decahedral and icosahedron Ag NPs, were embedded into PEDOT:PSS as HTLs for OPVs. • PCE was increased from 5.8% to 6.5 (decahedral-based) and 6.3% (icosahedron-based) based on similar active layer. • The active layer did not show any aggregation and morphology change after adopting hybrid HTL films into the devices. [ABSTRACT FROM AUTHOR]

Effect of various concentrations of fabricated cobalt oxide (Co3O4) nanoparticles (NPs) in the active layer of different donors and acceptors based hybrid organic bulk heterojunction-BHJ devices were investigated using inverted architecture. The organic active layer comprising different donors P3HT (poly(3-hexylthiophene-2,5-diyl) and PTB7 (Poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b] thiophenediyl]][6,6]) and acceptor (phenyl-C-butyric acid methyl ester (PC60BM and PC70BM) materials. The incorporation of NPs in the binary blends of P3HT:PC60BM and PTB7:PC70BM enhanced the power conversion efficiency (PCE) of resulting ternary devices. This increase in PCE is mostly due to decrease in series resistance (Rs) with an optimum amount of Co3O4 in the organic photoactive layer. It was found that the ternary blend has higher absorbance relative to a binary blend of P3HT:PCBM. Addition of NPs in the active materials blend increased film roughness and form interpenetrating network to facilitate charges transportation in the active layer. The higher amount of NPs enhanced agglomerations which caused to break down the BHJ led to decrease the performance of the ternary devices. [ABSTRACT FROM AUTHOR]

The impact of PCBM and PCBM on the thermal stability of two low-bandgap conjugated polymers widely used in organic photovoltaic applications, namely PTB7 and PTB7-Th (also known as PBDTTT-EFT), was studied under nitrogen and air atmospheres. The thermal stability effect observed is mainly additive, i.e., the stability of the composites is similar to the weighted average of the stabilities of the individual components. The thiophene-substituted polymer (PTB7-Th) displays higher thermal stability, both in nitrogen and air, than its ether-substituted analogue (PTB7). The corresponding bulk heterojunction composites display the same order of relative thermal stabilities, i.e., PTB7-Th:PC71BM (1:1.5) > PTB7:PC71BM (1:1.5), which interestingly is also the order of lifetime stabilities reported in the literature for the corresponding OPV devices. These results suggest that simple and rapid thermogravimetry tests might be used as a valid rapid screening test to infer on the relative lifetime stability of OPV devices. [ABSTRACT FROM AUTHOR]

Polymer solar cells (PSCs) have gained immense research interest in the recent years predominantly due to low-cost, solution process-ability, and facile device fabrication. However, achieving high stability without compromising the power conversion efficiency (PCE) serves to be an important trade-off for commercialization. In line with this, we demonstrate the significance of incorporating a CsI/ZnO bilayer as electron transport layer (ETL) in the bulk heterojunction PSCs employing low band gap polymer (PTB7) and fullerene (PC 71 BM) as the photo-active layer. The devices with CsI/ZnO interlayer exhibited substantial enhancement of 800% and 12% in PCE when compared to the devices with pristine CsI and pristine ZnO as ETL, respectively. Furthermore, the UV and UV-ozone induced degradation studies revealed that the devices incorporating CsI/ZnO bilayer possess excellent decomposition stability (∼23% higher) over the devices with pristine ZnO counterparts. The incorporation of CsI between ITO and ZnO was found to favorably modify the energy-level alignment at the interface, contributing to the charge collection efficiency as well as protecting the adjacent light absorbing polymer layers from degradation. The mechanism behind the improvement in PCE and stability is analyzed using the electrochemical impedance spectroscopy and dark I–V characteristics. [ABSTRACT FROM AUTHOR]

Abstract: We have developed two new electron acceptors NAP‐C60 and N4 derived from naphthalene and fluorene, respectively for solution processed organic solar cells. In the case of NAP‐C60, [6, 6]‐phenyl C61‐butyric acid methyl ester (PC61BM) basic structure is modified by replacing its phenyl group with naphthalene group; while in the case of N4, diaryl fullerene structure was modified using fluorene group. The UV‐visible spectra of the molecules show strong absorption in the UV region. Cyclic‐voltammetry measurements yielded the highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels of N4 and NAP‐C60 molecules as (‐5.63 eV, −3.69 eV) and (5.80 eV, −3.70 eV), respectively. The best solar cell devices made from PTB7:NAP‐C60 and PTB7:N4 bulk composite films resulted in power conversion efficiencies of 4.1 and 4.3 %, respectively. The diarylmethanofullerene derivative N4 shows a higher open circuit voltage compared to the methanofullerene derivative NAP‐C60, attributed to low lying LUMO levels of N4. [ABSTRACT FROM AUTHOR]

In this article, we attempt to demonstrate a way of tackling one of the biggest challenges in the path of commercialization of organic solar cells, the initial photo-degradation of the cells known as “burn-in”. The “burn-in” phenomenon is most prominent during the first few hours of device operation under illumination and responsible for losing 25% or more fraction of the initial efficiency. To address this major issue, we have studied photo degradation of inverted organic solar cells with plain Zinc Oxide (ZnO) and Aluminum doped ZnO (AZO) as an electron transport layer over a short time period of 5 h during which the degradation is most severe. The study has been done on two different device structures containing both crystalline and amorphous polymers (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}{3-fluoro-2-[(2 ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl}), respectively). Application of an AZO layer as the electron transport layer resolves the issue of photo-degradation in both cases, regardless of the polymer used in the active layer. AZO layer is found to provide less charge accumulation and better charge extraction at cathode/active layer interface. Mott-Schottky analysis shows modification of cathode interfacial layer work function and enhancement of open-circuit voltage due to the introduction of doped ZnO as electron transport layer. The exaltation persists even after the ageing of the devices. The devices with AZO layer retain their initial efficiency (almost 100%) even after photo-degradation while the device with pristine ZnO layer loses up to 60% of the initial efficiency. [ABSTRACT FROM AUTHOR]

Polymer solar cells (PSCs) are considered as one of the most promising low-cost alternatives for renewable energy production with devices now reaching power conversion efficiencies (PCEs) above the milestone value of 10%. These enhanced performances were achieved by developing new electron-donor (ED) and electron-acceptor (EA) materials as well as finding the adequate morphologies in either bulk heterojunction or sequentially deposited active layers. In particular, producing adequate vertical concentration gradients with higher concentrations of ED and EA close to the anode and cathode, respectively, results in an improved charge collection and consequently higher photovoltaic parameters such as the fill factor. In this review, we relate processes to generate active layers with ED–EA vertical concentration gradients. After summarizing the formation of such concentration gradients in single layer active layers through processes such as annealing or additives, we will verify that sequential deposition of multilayered active layers can be an efficient approach to remarkably increase the fill factor and PCE of PSCs. In fact, applying this challenging approach to fabricate inverted architecture PSCs has the potential to generate low-cost, high efficiency and stable devices, which may revolutionize worldwide energy demand and/or help develop next generation devices such as semi-transparent photovoltaic windows. [ABSTRACT FROM AUTHOR]

The use of fullerene as acceptor limits the thermal stability of organic solar cells at high temperatures as their diffusion inside the donor leads to phase separation via Ostwald ripening. Here it is reported that fullerene diffusion is fully suppressed at temperatures up to 140 °C in bulk heterojunctions based on the benzodithiophene-based polymer (the poly[[4,8-bis[(2-ethylhexyl)oxy]-benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]-thieno[3,4-b]thiophenediyl]], (PTB7) in combination with the fullerene derivative [6,6]-phenyl-C71-butyric acid methyl ester (PC70BM). The blend stability is found independently of the presence of diiodooctane (DIO) used to optimize nanostructuration and in contrast to PTB7 blends using the smaller fullerene derivative PC70BM. The unprecedented thermal stability of PTB7:PC70BM layers is addressed to local minima in the mixing enthalpy of the blend forming stable phases that inhibit fullerene diffusion. Importantly, although the nanoscale morphology of DIO processed blends is thermally stable, corresponding devices show strong performance losses under thermal stress. Only by the use of a high temperature annealing step removing residual DIO from the device, remarkably stable high efficiency solar cells with performance losses less than 10% after a continuous annealing at 140 °C over 3 days are obtained. These results pave the way toward high temperature stable polymer solar cells using fullerene acceptors. [ABSTRACT FROM AUTHOR]

Semitransparent organic solar cells are a promising approach to smart window applications and building integration. Here, we demonstrate a high performance semitransparent organic solar cell that incorporates the low bandgap polymer, PTB7, in the photoactive layer and a simple, non-patterned Dielectric/Metal/Dielectric or D/M/D anode (MoO 3 /Ag/MoO 3 ). The combination of excellent photovoltaic properties of PTB7:PC 71 BM based solar cell and transparency of the MoO 3 /Ag/MoO 3 anode resulted in an impressive power conversion efficiency of 5% at 18.3% visible light transmission. By tuning the active layer and outer MoO 3 layer thicknesses, devices with ∼25% average visible transmission were fabricated, which is considered as a benchmark transmittance for window applications. Transfer matrix modelling (TMM) was used to optimise the active layer and electrode thickness in terms of the optical field in the active layer. Additionally, the color rendering ability was found to be dependent on the active layer thickness, as well as the electrode. Device properties were studied from the perspectives of color rendering property, photovoltaic performance and theoretical optical field distribution. [ABSTRACT FROM AUTHOR]

The chemical degradation of the Poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5- b' ]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4- b ]thiophenediyl]] or ‘ PTB7’ has been studied using X-ray Photoelectron Spectroscopy (XPS). This material system appears to be intrinsically unstable especially when illuminated in air and XPS studies confirm the rapid photo-degradation is related to changes in chemical structure of the polymer. In particular, XPS spectra show an initial reduction in relative C C intensity, suggests loss of the alkoxy side chains. This is followed by a dramatic increase in the level of oxygen-bonded species, especially C O at ∼286.5 eV and C(=O)O at 289.2 eV, indicative of COOH and OH group formation, and oxidation of S. The XPS results support the view that using processing additives reduces the chemical stability of the polymer and provides insight into strategies to improve molecular design to ensure higher chemical stability. [ABSTRACT FROM AUTHOR]

Two new perylenediimides (PDIs) have been developed for use as electron acceptors in solution-processed bulk heterojunction solar cells. The compounds were designed to exhibit maximal solubility in organic solvents, and reduced aggregation in the solid state. In order to achieve this, diphenylphenoxy groups were used to functionalize a monomeric PDI core, and two PDI dimers were bridged with either one or two thiophene units. In photovoltaic devices prepared using PDI dimers and a monomer in conjunction with PTB7, it was found that the formation of crystalline domains in either the acceptor or donor was completely suppressed. Atomic force microscopy, X-ray diffraction, charge carrier mobility measurements and recombination kinetics studies all suggest that the lack of crystallinity in the active layer induces a significant drop in electron mobility. Significant surface recombination losses associated with a lack of segregation in the material were also identified as a significant loss mechanism. Finally, the monomeric PDI was found to have sub-optimum LUMO energy matching the cathode contact, thus limiting charge carrier extraction. Despite these setbacks, all PDIs produced high open circuit voltages, reaching almost 1 V in one particular case.

This paper reports a ZnO Nanoparticles (NPs)/CH 3 NH 3 PbI 3 /PTB7/MoO 3 /Ag inverted structure based UV–visible-Near Infrared (NIR) broadband photodetector fabricated on the fluorine-doped tin oxide (FTO) coated glass substrate. ZnO NPs layer acts as the electron transport layer (ETL), CH 3 NH 3 PbI 3 acts as the active layer, PTB7 acts as the hole transport layer (HTL) and MoO 3 is used to optimize the recombination current in the proposed photodetector structure. Spin coating method has been used for depositing the layers of ZnO NPs, CH 3 NH 3 PbI 3 and PTB7 in the proposed structure while the MoO 3 layer has been grown by the thermal evaporation method. The optical measurements over 350–850 nm wavelength range give the maximum photoresponsivity, detectivity and external quantum efficiency (EQE) of ∼0.36 A/W, ∼7.8x1012 Jones and ∼83.67% under −2 V, respectively. The proposed photodetector gives a rise time and fall time of 81 ms and 75 ms, respectively. [ABSTRACT FROM AUTHOR]

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Indene-C 60 bisadduct (ICBA) is one of the rare acceptors which can supersede commonly used phenyl-C71-butyric acid methyl ester (PCBM70) in enhancing the performance of bulk heterojunction (BHJ) solar cells owing to its shallower lowest unoccupied molecular orbital (LUMO) level. However, ICBA tends to decrease the photocurrent for most of the low band-gap polymers synthesized to date. Here we examine the interaction of ICBA with the one of the popular low band-gap polymers poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl) carbonyl] thieno[3,4- b ]thiophenediyl]] (PTB7), at femtosecond level, to explore key dynamics governing the operation of BHJ cells involving ICBA. The photo-physics of binary and ternary systems based on PTB7 coupled with PCBM70 and/or ICBA are studied by means of transient absorption spectroscopy (TAS) and electrochemical impedance spectroscopy (EIS) and supported by morphology analysis. Our study suggests that both inefficient charge-separation and poor charge transport of ICBA is responsible for relatively low photocurrent generation. [ABSTRACT FROM AUTHOR]

It has been well known that incorporation of nano-heterostructures of various metals, semiconductors and dielectric materials in the active layer of organic solar cells (OSCs) helps in improving power conversion efficiency (PCE). In the present study, we demonstrated microwave synthesis of CdS nanoparticles (NPs) for their application in one of most efficient OSCs consisting of poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl] [3-fluoro-2-[(2-ethylhexyl)carbonyl] thieno[3,4-b]thiophenediyl]] (PTB7): [6,6]-phenyl C 71 -butyric acid methyl ester (PCBM) photoactive blend. This is crucial to fully explore the promising features of low cost and scalability in organic-inorganic hybrid solar cells. Synthesized CdS NPs are slightly elongated and highly crystalline with their absorption lies in the visible region as confirmed by High resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), UV–Vis absorption spectroscopy studies. Our experimental results for the devices in an inverted geometry having a structure ITO/ZnO/PTB7: CdS: PCBM/MoO 3 /Ag has shown increase in Jsc and PCE by nearly 10%. However, it was observed that this increase is only when NPs were added in the low concentration in active layer. UV–Vis absorption spectroscopy, Photoluminescence (PL) and atomic force microscopy (AFM) studies were carried out in order understand the device performance. [ABSTRACT FROM AUTHOR]

Among the new materials currently employed as electron donor element in active layers of organic solar cells (OSCs), PTB7 holds the best results. It has been extensively studied and now there is a search for new derivatives to improve its properties. In this work, a set of 24 polymers derived from polythieno[3,4-b]-thiophene-co-benzodithiophene (PTB7) was studied theoretically, using chemical modifications in the benzodithiophene (BDT) moiety of the PTB7 monomeric units. After evaluations of the electronic and optical properties, including the open circuit voltage and exciton dissociation and recombination conditions, the results indicate that employing chlorine as substituent yields the most promising material for application in active layers together with Phenyl-C 61 -Butyric-Acid-Methyl-Ester (PCBM) as electron acceptor material. [ABSTRACT FROM AUTHOR]

Optical sensing from the near ultra-violet to the visible range of light is very important for industrial process monitoring, health care, and life science. Here, we present organic photodiodes (OPD), operating between 300 and 750 nm wavelength fabricated in bottom absorption geometry with the semiconducting polymer blend PTB7:PC 71 BM. A maximal responsivity of ~ 100 mA/W at 630 nm with 54 mW/cm 2 light intensity has been achieved at room temperature. An approach to improve the on/off-ratio (light to dark) by modifying the absorption layer thickness has been investigated. The dark current decreases with the thickness of polymer blend PTB7:PC 71 BM. The transient response for OPD rise- and fall-time is in the μs regime, with an on/off-ratio of four orders of magnitude at − 2 V bias. The rise of responsivity is tunable by increasing the absorption layer thickness and shows a dependency in relation to dark current and transient response. [ABSTRACT FROM AUTHOR]

Performance losses and aging mechanisms are investigated in state-of-the-art PTB7:PC70BM solar cells. Inverted devices incorporating a vanadium pentoxide (V2O5) top contact have efficiencies of 8%. After aging the unencapsulated devices, no changes are observed in the open circuit voltage ( Voc) or short circuit current ( Jsc); however, the fill factor (FF) drops from 0.7 to 0.61. An s-shape initially appears in the J- V curve after aging, which can be reduced by cycling through the J- V curve under illumination. This is discussed in context of the redox properties of V2O5. With impedance spectroscopy, it is demonstrated that changes to the contact interfaces are completely reversible and not responsible for the performance loss. Intensity modulated photocurrent spectroscopy combined with device modeling reveals that the loss in FF is due to trap formation in the active layer. Additionally it is observed that the performance of pristine devices is limited by optical absorption in the thin active layer and the build-up of space charge which hinders carrier extraction. [ABSTRACT FROM AUTHOR]

Formic acid (FA) was used as a novel additive in bulk heterojunction (BHJ) solar cells, which contains blends of poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophene-4,6-diyl]] (PTB7) and [6,6]-phenyl-C71-butyric acid methyl ester (PC 71 BM). The effect of FA on the performance of PTB7:PC 71 BM based BHJ solar cells is investigated. By the incorporation of FA, the device with the ratio of 6 vol % shows the best power conversion efficiency (PCE) of 9.04%, along with the short-circuit current density ( J sc ), open-circuit voltage ( V oc ), and fill factor (FF) being 24.11 mA/cm 2 , 0.72 V, and 52.11%, respectively. Experimental results suggest that FA has a strong influence on charge carrier dynamics with a significant increase in J sc by ∼65% and the dramatically enhanced PCE is mainly due to the increase of absorption and exciton generation of the active layers and the improved charge-carrier mobility of the devices. [ABSTRACT FROM AUTHOR]

Active layer thickness-dependent internal quantum efficiencies (IQE) of photocurrent within bulk heterojunction organic photovoltaic (OPV) devices were characterized. These active layers consisted of an electron-donating narrow band-gap polymer and an electron-accepting fullerene derivative. In order to calculate IQE spectra as a function of active layer thickness, incident photon-to-current conversion efficiency (IPCE) spectra and internal absorptance spectra of active layers with various thicknesses were estimated in these solar cell devices. The transfer matrix method (TMM) was used to calculate the internal absorptance spectra of active layers by using experimental optical constants of thin layers typical for these types of OPV devices including narrow band-gap polymer blend film. In addition, spatially resolved absorptance spectra were used to analyze obtained IPCE spectra as well as OPV device parameters (e.g., short circuit current density) at various active layer thicknesses. Finally, charge-carrier-collecting probability as a function of active layer thickness was suggested with which the relationship between initial exciton generation and final power conversion efficiency can be more quantitatively described. [ABSTRACT FROM AUTHOR]

We report on bulk-heterojunction solar cells fabricated based on ternary mixed solutions of two donors of poly[[4,8-bis[(2-ethylhexyl)oxy]benzo [1,2-b:4,5-b’] dithiophene-2, 6-diyl] [3-fluoro-2- [(2-ethylhexyl) carbonyl]thieno[3,4-b]-thiophenediyl] (PTB7) and [N-9’-heptadecanyl-2,7-carbazole-alt-5,5-(4’,7’-di-2-thienyl-2’,1’,3’-benzothiadiazole)] (PCDTBT), and an accepter of [6,6]-phenyl C71butyric acid methyl ester (PC71BM). The solar cells had a glass/ITO/NiO/PTB7:PCDTBT:PC71BM/LiF/Al structure. Solar cells containing a 1-2% PCDTBT weight fraction showed a noticeable improvement in short circuit current density (Jsc), fill factor (FF), and power conversion efficiency (PCE). Solar cells with a 2% PCDTBT weight fraction exhibited an open circuit voltage (Voc) of 0.77 V,Jscof 13 mA/cm2, FF of 0.42, and PCE of 4.23%. Possible mechanisms for the solar cell performance improvement by the introduction of the small amount of PCDTBT in the PTB7:PC71BM active layer was discussed based on the active layer morphology changes and carrier transport mechanisms. [ABSTRACT FROM AUTHOR]

Nickel oxide (NiO) has become attractive as a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT :PSS) substitute in solar cells’ hole transport layers (HTLs). However, solar cells with NiO HTLs based on poly[[4,8-bis[(2-ethylhexyl)oxy]benzo [1,2-b:4,5-b′]dithiophene-2,6-diyl] [3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]-thiophenediyl] (PTB7) and [6,6]-phenyl C71butyric acid methyl ester (PC71BM) remain poorly characterized. We report the effects of NiO-layer thickness on the performance of glass/ITO/NiO/PTB7:PC71BM/LiF/Al-structured solar cells. Thickness was optimized by changing nickel acetate tetrahydrate concentration in 2-methoxyethanol solution used for spin-coating deposition. We achieved a power conversion efficiency of 5.14% at 0.2 M of nickel acetate tetrahydrate. Solar cells with NiO HTLs exhibited improved long-term reliability. [ABSTRACT FROM AUTHOR]

We report the fabrication of polymer/inorganic hybrid solar cells (HSCs) based on CdSe nanorods (NRs) and the semiconducting polymer PTB7. The power conversion efficiency of HSCs can be significantly enhanced by engineering the polymer/nanocrystal interface with ethanedithiol (EDT) and 1,4-benzenedithiol (1,4-BDT) treatments and reached 2.58% and 2.79%, respectively. These results were preferable to that of a pyridine-coated NR-based device (1.75%). This improvement was attributed to the thiol groups of EDT and 1,4-BDT, which can tightly coordinate the Cd ions to form Cd-thialate on CdSe NR surfaces, thereby effectively passivating the NR surface and reducing the active layer defects. Therefore, the rate of exciton generation and dissociation was enhanced and led to the improvement of the device performance. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

We studied the performance over time of opaque and semi-transparent PTB7:PC71BM bulk hetero-junction solar cells. For unsealed inverted configuration cells we observe that when the isolation from the environment is improved, the degradation observed is dominated by one single exponential decay. We demonstrate that a dielectric multilayer stack of approximately 550 nm provides an isolation that increases the lifetime of the cell close to ten times. In that event the fill factor appears to be the PV parameter dominating cell degradation resulting from a decrease in the shunt resistance. An Impedance analysis we performed indicates that a Warburg element, attributed to the presence of slowly moving charges such as heavy ions, must be included in the description of the experimental data. The contribution from such element increases as the cell degrades in good agreement with a degradation dominated by the corrosive effects from external agents reaching the active layer of the device. [ABSTRACT FROM AUTHOR]