A star-shaped conjugated molecule featuring a triazole core and diketopyrrolopyrrole branches is an efficient electron-selective interlayer for inverted polymer solar cells

A novel triazole-cored, star-shaped, conjugated molecule (TDGTPA) has been synthesized for use as an electron-selective interlayer in inverted polymer solar cells (PSCs). This star-shaped molecule comprised a triazole unit as the central core, 2,5-thienyl diketopyrrolopyrrole units as π-conjugated bridges, and tert-butyl-substituted triphenylamine units as both end groups and donor units. The inverted PSC had the device structure indium tin oxide/ZnO/TDGTPA/poly(3-hexylthiophene) (P3HT)/fullerene derivative (PC₇₁BM)/MoO₃/Ag. Inserting TDGTPA as the electron-selective layer enhanced the compatibility of the ZnO-based electron transport layer and the P3HT:PC₇₁BM blend-based photoactive layer. The low energy of the lowest unoccupied molecular orbital (−3.98 eV) of TDGTPA was favorable for electron transfer from the photoactive layer to the ZnO layer, thereby enhancing the photovoltaic performance of the PSC. The photo-conversion efficiency of the device incorporating TDGTPA as the electron-selective layer was 15.8% greater than that of the corresponding device prepared without it.

A novel triazole-cored, star-shaped, conjugated molecule (TDGTPA) has been synthesized for use as an electron-selective interlayer in inverted polymer solar cells (PSCs).

Embedding a Diketopyrrolopyrrole-Based Cross-linking Interfacial Layer Enhances the Performance of Organic Photovoltaics

In this study, we prepared DPPBTDA, a diketopyrrolopyrrole-based small molecule presenting a terminal cross-linkable azido group, as a cathode modifying layer for organic photovoltaics (OPVs) having the inverted device structure glass/indium tin oxide/zinc oxide (ZnO) with or without the interfacial layer (IFL)/active layer/MoO₃/Ag. The active layer comprising a blend of poly[4,8-bis(5-(2-ethylhexyl)thien-2-yl)benzo[1,2- b;4,5- b']dithiophene-2,6-diyl- alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4- b]thiophene)-2-carboxylate-2,6-diyl] (PTB7-Th) as the electron donor and [6,6]-phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM) as the electron acceptor. Atomic force microscopy, space-charge-limited current mobility, surface energy, electron spectroscopy for chemical analysis depth profile, ultraviolet photoelectron spectroscopy analysis, and OPV performance data revealed that the surface status of ZnO changed after inserting the DPPBTDA/PCBM hybrid IFL and induced an optimized blend morphology, having a preferred gradient distribution of the conjugated polymer and PC₇₁BM, for efficient carrier transport. The power conversion efficiency (AM 1.5 G, 1000 W m^-2) of the device incorporating the hybrid IFL increased to 9.4 ± 0.11% from 8.5 ± 0.15% for the preoptimized PTB7-Th/PCBM device (primarily because of an enhancement in the fill factor from 68.7 ± 1.1 to 72.1 ± 0.8%).

Design and synthesis of N-substituted perylene diimide based low band gap polymers for organic solar cell applications

In this study, we report on the synthesis and device studies of a series of new copolymers containing N-substituted perylene dimide and dioctylfluorene units as part of the main backbone. A facile synthetic approach avoiding non-selective bromination was used to synthesize the monomer M1 by the reaction of perylene-3,4,9,10-tetracarboxylic dianhydride with 2-amino-7-bromo-9,9-dioctylfluorene. The copolymers P1 and P2 were synthesized by Suzuki polycondensation of M1 with 2,2′-(9,9-dioctyl-9H-fluoren-2,7-diyl)bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolane) M2 and 9-(heptadecan-9-yl)-2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9H-carbazole M3, respectively. The copolymer P3 was synthesized by direct arylation polymerization of M1 with 4,7-bis(4-octylthiophen-2-yl)benzo[c]-1,2,5-thiadiazole M4. All the copolymers showed thermal stability greater than 380 °C as evidenced from thermogravimetric analysis. The copolymers exhibited a narrow optical band gap (1.80–2.08 eV) with their UV-visible absorption spectra extending up to the NIR region and they are found to be suitable for use in OSC applications. The molecular weights of the polymers P1–P3 were found to be in the range of 10.68 to 16.02 kg mol⁻¹ as measured from GPC analysis. The surface morphology of the active layers based on P1/P2/P3:P3HT blend films was investigated by AFM and the rms values from height images range from 0.65 to 2.90 nm. The polymers were blended with P3HT to fabricate BHJ solar cells in three different weight ratios i.e. 1 : 1, 1.5 : 1 and 2 : 1 and the best power conversion efficiency was observed for the binary film of P3:P3HT blend device in a 1 : 1 weight ratio which reached up to 1.96% with a V_oc of 0.55 V, J_sc of 10.12 mA cm⁻² and FF of 34.63% which is among the highest reported for BHJ solar cells with N-substituted PDI based acceptors.

Newly designed N-substituted perylene diimide based acceptor copolymers have been characterized and tested for organic solar cells with P3HT in different weight ratios.

Oleylamine-functionalized graphene oxide as an electron block layer towards high-performance and photostable fullerene-free polymer solar cells

Oleylamine-functionalized graphene oxide (GO) has a shallower energy level of conduction band (E_CB) and a deeper energy level of the valence band (E_VB) as compared to common hole extraction layer (HEL) materials, which make the electron block layer (EBL). Photoluminescence, X-ray photoelectron spectroscopy (XPS), and current density-voltage (J-V) curves with a large reverse bias voltage range obtained under dark conditions are used to determine whether GO layers play important roles in blocking the electron transport to the MoO₃/Ag composite anode and prevent MoO₃ diffusion into a photoactive layer under light illumination. Moreover, GO inserted between a photoactive layer and an HEL enhances charge carrier transport and collection and avoids the monomolecular recombination between the photoactive layer and HEL. Photovoltaic parameters and photostability measurements of inverted and forward PSCs have shown that upon introduction of GO, the performance and photostability of PSCs are improved. On adding GO to PSCs, the power conversion efficiency (PCE) increases approximately 5% and 4% and reduces the decay ratio to approximately 50% and 65% of the initial value for the inverted and forward PSCs, respectively.

Improved electron extraction by a ZnO nanoparticle interlayer for solution-processed polymer solar cells

Solvent effect on hole-blocking layers based on ZnO nanoparticles is investigated for solution-processed polymer solar cells. Incorporation of the dense ZnO nanoparticle interlayer leads to enhanced PCEs in PTB7-Th:PC₇₁BM solar cells from 8.4% to 9.2% with improved stability.

Recent Development of Plasmonic Resonance-Based Photocatalysis and Photovoltaics for Solar Utilization

Increasing utilization of solar energy is an effective strategy to tackle our energy and energy-related environmental issues. Both solar photocatalysis (PC) and solar photovoltaics (PV) have high potential to develop technologies of many practical applications. Substantial research efforts are devoted to enhancing visible light activation of the photoelectrocatalytic reactions by various modifications of nanostructured semiconductors. This review paper emphasizes the recent advancement in material modifications by means of the promising localized surface plasmonic resonance (LSPR) mechanisms. The principles of LSPR and its effects on the photonic efficiency of PV and PC are discussed here. Many research findings reveal the promise of Au and Ag plasmonic nanoparticles (NPs). Continual investigation for increasing the stability of the plasmonic NPs will be fruitful.