We studied the thermoelectric properties of a diketopyrrolopyrrole-based semiconductor (PDPP3T) via a precisely tuned doping process using Iron (III) chloride. In particular, the doping states of PDPP3T film were linearly controlled depending on the dopant concentration. The outstanding Seebeck coefficient of PDPP3T assisted the excellent power factors (PFs) over 200 μW m−1K−2 at the broad range of doping concentration (3–8 mM) and the maximum PF reached up to 276 μW m−1K−2, which is much higher than that of poly(3-hexylthiophene), 56 μW m−1K−2. The high-mobility of PDPP3T was beneficial to enhance the electrical conductivity and the low level of total dopant volume was important to maintain high Seebeck coefficients. In addition, the low bandgap PDPP3T polymer effiectively shifted its absorption into near infra-red area and became more colorless after doping, which is great advantage to realize transparent electronic devices. Our results give importance guidance to develop thermoelectric semiconducting polymers and we suggest that the use of low bandgap and high-mobility polymers, and the accurate control of the doping levels are key factors for obtaining the high thermoelectric PF.

While the outstanding charge transport and sunlightharvesting properties of porphyrin molecules are highly attractive as active materials for organic photovoltaic (OPV) devices, the development of ntype porphyrin-based electron acceptors has been challenging. In this work, we developed a high-performance porphyrin-based electron acceptor for OPVs by substitution of four naphthalene diimide (NDI) units at the perimeter of a Zn-porphyrin (P Zn ) core using ethyne linkage. Effective πconjugation between four NDI wings and the P Zn core significantly broadened Q-band absorption to the near infrared region, thereby achieving the narrow band gap of 1.33 eV. Employing a windmill-structured tetra-NDI substituted P Zn -based acceptor (P Zn -TNDI) and mid-band gap polymer donor (PTB7-Th), the bulk heterojunction OPV devices achieved a power conversion efficiency (PCE) of 8.15% with an energy loss of 0.61 eV. The PCE of our P Zn -TNDI-based device was the highest among the reported OPVs using porphyrin-based acceptors. Notably, the amorphous characteristic of P Zn -TNDI enabled optimization of the device performance without using any additive, which should make industrial fabrication simpler and cheaper.

Porphyrin derivatives have recently emerged as hole transport layers (HTLs) because of their electron-rich characteristics. Although several successes with porphyrin-based HTLs have been recently reported, achieving excellent solar cell performance, the chances to improve this further by molecular engineering are still open. In this work, Zn porphyrin (PZn)-based HTLs were developed by conjugating fluorinated triphenylamine (FTPA) wings at the perimeter of the PZn core for low-temperature perovskite solar cells (L-PSCs). The fluorinated PZn-HTLs (PZn–2FTPA and PZn–3FTPA) exhibited superior HTL properties compared to the nonfluorinated one (PZn–TPA). Moreover, their deeper highest occupied molecular orbital energy levels were beneficial for boosting open-circuit voltages, and their enhanced face-on stacking improved the hole transport properties. The L-PSC using PZn–2FTPA achieved the highest performance of 18.85%. Thus far, this result is one of the highest reported power conversion efficiencies among the PSCs using porphyrin-based HTLs.

Small-bundled single-walled carbon nanotube (SSWCNT) nanocomposite films with two different conjugated polymers were facilely prepared by using a micronizing mill. The influence of the difference in the electronic structures and molecular orientations of poly­(3-hexylthiophene) (P3HT) and poly­(diketopyrrolo­pyrrole–selenophene) (PDPPSe) on the thermoelectric properties of polymer/SSWCNT nanocomposites was systematically investigated. Planar-shaped PDPPSe with stronger π–π interaction, compared to that in P3HT, naturally forms a dense surface microstructure with SSWCNT by easily wrapping the SSWCNT surface. Furthermore, the inherent crystalline orientation of PDPPSe effectively enhances the electrical conductivity of the SSWCNT nanocomposite film by inducing the alignment of SSWCNT bundles in an in-plane direction. In the electronic structure of the composite, PDPPSe lowers the interfacial energy barrier between the polymer and SSWCNT to induce the carrier-filtering effect, which can facilitate charge transport from the polymer to SSWCNT. The PDPPSe/SSWCNT nanocomposite exhibits a considerably increased electrical conductivity of 537.7 S cm–1 and a higher Seebeck coefficient of 62.5 μV K–1 compared to those of the P3HT/SSWCNT nanocomposite. The optimized power factor of the PDPPSe/SSWCNT nanocomposite is 210 μW m–1 K–2, which is about 10 times higher than that of the P3HT/SSWCNT nanocomposite. The thermoelectric generator fabricated from PDPPSe/SSWCNT displays a high open-circuit voltage (V oc) of 8.5 mV and short-circuit current (I sc) of 162.8 μA, resulting in a maximum output power of 0.35 μW at ΔT = 10 °C.

The susceptibility of porphyrin derivatives to light‐harvesting and charge‐transport operations have enabled these materials to be employed in solar cell applications. The potential of porphyrin derivatives as hole‐transporting materials (HTMs) for perovskite solar cells (PSCs) has recently been demonstrated, but knowledge of the relationships between the porphyrin structure and device performance remains insufficient. In this work, a series of novel zinc porphyrin (PZn) derivatives has been developed and employed as HTMs for low‐temperature processed PSCs. Key to the design strategy is the incorporation of an electron‐deficient pyridine moiety to down‐shift the HOMO levels of porphyrin HTMs. The porphyrin HTMs incorporating diphenyl‐2‐pyridylamine (DPPA) have HOMO levels that are in good agreement with the perovskite active layers, thus facilitating hole transfers from the perovskite to the HTMs. The DPPA‐containing zinc porphyrin‐based PSCs gave the best performance, with efficiency levels comparable to those of PSCs using spiro‐OMeTAD, a current state‐of‐the‐art HTM. In particular, PZn–DPPA‐based PSCs show superior air stability, in both doped and undoped forms, to spiro‐OMeTAD based devices.

No abstract

The development of n-type porphyrin acceptors is challenging in organic solar cells. In this work, we synthesized a novel n-type porphyrin acceptor, PZn-TNI, via the introduction of the electron withdrawing naphthalene imide (NI) moiety at the meso position of zinc porphyrin (PZn). PZn-TNI has excellent thermal stability and unique bimodal absorption with a strong Soret band (300–600 nm) and weak Q-band (600–800 nm). The weak long-wavelength absorption of PZn-TNI was completely covered by combining the low bandgap polymer donor, PTB7-Th, which realized the well-balanced panchromatic photon-to-current conversion in the range of 300–800 nm. Notably, the one-step reaction of the NI moiety from a commercially available source leads to the cheap and simple n-type porphyrin synthesis. The substitution of four NIs in PZn ring induced sufficient n-type characteristics with proper HOMO and LUMO energy levels for efficient charge transport with PTB7-Th. Fullerene-free organic solar cells based-on PTB7-Th:PZn-TNI were investigated and showed a promising PCE of 5.07% without any additive treatment. To the best of our knowledge, this is the highest PCE in the porphyrin-based acceptors without utilization of the perylene diimide accepting unit.