Zhan'ao Tan

High‐Performance Inverted Polymer Solar Cells with Solution‐Processed Titanium Chelate as Electron‐Collecting Layer on ITO Electrode

High-performance inverted polymer solar cells (PSCs) with solution-processed titanium chelate TIPD as electron collecting layer are reported. The power conversion efficiency (PCE) of the inverted PSC with a-TIPD buffer layer with thermal annealing at 150 °C for 10 min reached 7.4% under the illumination of AM1.5, 100 mW/cm(2), which is increased by 16% in comparison with that (6.4%) of the device in the conventional structure. The PCE of 7.4% is the highest among the inverted PSCs reported so far in the literature.

Near‐Band‐Edge Electroluminescence from Heavy‐Metal‐Free Colloidal Quantum Dots

The band-edge electroluminescence (EL) of colloidal QDs of cadmium compounds, i.e., Cd(S,Se,Te), exhibits sizetunable spectral emission (450–760 nm) and narrow bandwidth (FWHM ∼ 30–40 nm), allowing for the design and fabrication of color-saturated red, green and blue (RGB) QD-LEDs with simple device confi gurations and high spectral purities that outperform those of liquid crystal displays and organic light emitting diodes. The maximum brightness of RGB QD-LEDs has improved by three orders of magnitude in less than one decade and exceeds 15 000 cd/m 2 for red emitters, corresponding to a current effi ciency of ∼ 2.3 cd/A. [ 15 ] With mercury and lead saltsbased colloidal nanocrystals (HgTe and Pb(S,Se)), the emission

Solution-processable metal oxides/chelates as electrode buffer layers for efficient and stable polymer solar cells

The interfaces between the electrodes and the photoactive layer significantly influence the efficiency and stability of polymer solar cells (PSCs). By choosing suitable interfacial materials, the energetic barrier height at the interface could be reduced to form an ohmic contact with less series resistance, inducing high charge collection efficiency of the corresponding electrodes for holes or electrons. Solution-processable metal compounds, especially metal oxides and transition metal chelates, have the advantages of high charge carrier mobility, suitable work function, low cost, and high environmental stability, which make them attractive for applications as cathode and anode interfacial materials for efficient and stable PSCs. In this paper, we reviewed the recent progress on solution processable metal oxides and metal chelates as buffer layers in conventional and inverted PSCs. In the introduction section, we introduced the operating principles of conventional and inverted PSCs, followed by introducing the energy levels, optical properties, processing methods and characterization techniques of the buffer layers. In the second and third parts, we reviewed recent progress in materials for both anode and cathode buffer layers. Finally, we drew a conclusion and gave a perspective. We believe that solution-processable metal oxides and metal chelates will play a key role as buffer layers in the future fabrication of large area and flexible PSCs with high performance and long term stability.

Efficient all-polymer solar cells based on blend of tris(thienylenevinylene)-substituted polythiophene and poly[perylene diimide-alt-bis(dithienothiophene)]

A narrow band-gap alternating copolymer of perylene diimide and bis(dithienothiophene) (2) and a polythiophene derivative substituted by a tris(thienylenevinylene) conjugated side chain (4) are used as acceptor and donor, respectively, in all-polymer solar cells (SCs). The optimized device based on the blend of 4 and 2 in the ratio 3:1 (w/w) gives a short circuit current (Jsc) of 5.02 mA cm−2 and a power conversion efficiency of 1.48%, under simulated AM 1.5 illumination at 100 mW cm−2. These values are among the highest values reported for all-polymer SCs.

Bright Multicolor Bandgap Fluorescent Carbon Quantum Dots for Electroluminescent Light‐Emitting Diodes

Multicolor bandgap fluorescent carbon quantum dots (MCBF-CQDs) from blue to red with quantum yield up to 75% are synthesized using a solvothermal method. For the first time, monochrome electroluminescent light-emitting diodes (LEDs) with MCBF-CQDs directly as an active emission layer are fabricated. The maximum luminance of blue LEDs reaches 136 cd m-2 , which is the best performance for CQD-based monochrome electroluminescent LEDs.

Efficient and stable polymer solar cells with solution-processed molybdenum oxide interfacial layer

We report efficient and stable polymer solar cells (PSCs) based on poly(3-hexylthiophene) and various fullerene derivatives using solution processed, cost effective molybdenum oxide (s-MoOx) as an anode interfacial layer. The chemical structure of the obtained s-MoOx was characterized by FTIR and XPS. The s-MoOx layer exhibits high light transmittance and effective hole collection properties. The PSCs with the s-MoOx anode buffer layer show enhanced performance in comparison with PEDOT:PSS modified devices. The power conversion efficiency of the PSC based on P3HT:IC70BA with the s-MoOx anode buffer layer reached 6.57% under an illumination of AM1.5G at 100 mW cm−2. In addition, compared with PEDOT:PSS modified devices, PSCs with the s-MoOx anode buffer layer exhibit a much superior stability and longer lifetime.

A Hyperbranched Conjugated Polymer as the Cathode Interlayer for High‐Performance Polymer Solar Cells

An alcohol-soluble hyperbranched conjugated polymer HBPFN with a dimethylamino moiety is synthesized and used as a cathode interlayer. A PCE of 7.7% is obtained for PBDTTT-C-T/PC71 BM based solar cells. No obvious interfacial dipole is found at the interface between the active layer and HBPFN however, an interfacial dipole with the cathode could be one of the reasons for the enhanced performance.

Molecular Design toward Efficient Polymer Solar Cells with High Polymer Content

A novel polythiophene derivative, PBT1, was designed, synthesized, and applied in polymer solar cells (PSCs). This work provides a successful example of using molecular structure as a tool to realize optimal photovoltaic performance with high polymer content, thus enabling the realization of efficient photoabsorption in very thin films. As a result, an efficiency of 6.88% was recorded in a PSC with a 75 nm active layer.

Significant improvement of photovoltaic performance by embedding thiophene in solution-processed star-shaped TPA-DPP backbone

Solution-processed star-shaped triphenylamine (TPA) derivatives and dialkylated diketopyrrolopyrrole (DPP)-based small molecules have been widely studied because they both yield promising photon-to-electron conversion. However, the power conversion efficiency (PCE) of covalent star-shaped TPA-DPP derivatives is still very low. To design star-shaped TPA-DPP derivatives with better photovoltaic performance, we embedded a thiophene ring in between the TPA and DPP units, namely TPA-T-DPP, and reported the comparative studies of the optoelectronic and photovoltaic properties of TPA-DPP and TPA-T-DPP. Benefiting from the covalent thiophene bridges, compared to the TPA-DPP solid film, the TPA-T-DPP film showed enhanced light-harvesting ability, for instance, an improved absorptivity (Abs. = 1.72/100 nm vs. 1.23/100 nm), a broader absorption band (131 nm vs. 107 nm) and a narrower band gap (1.86 eV vs. 1.91 eV), from cyclic voltammetry. Studies on the photovoltaic properties revealed that the best TPA-T-DPP:PC71BM based device showed a dramatically enhanced PCE of 2.95%, increased by 2.14 times with respect to the efficiency of the best TPA-DPP based device (1.38%). The improvement of PCE also was observed in the small molecule:PC61BM based devices (1.81% vs. 1.13%). Test of the hole mobilites of the active layer provided further insight into the impact of the embedded thiophene units. The hole mobility of the TPA-T-DPP:PC71BM blended films was higher by about one order of magnitude (1.16 × 10−2 cm2 V−1 s−1) than that of the TPA-DPP:PC71BM blended films (3.85 × 10−3 cm2 V−1 s−1). These results clearly indicated that embedding the thiophene ring enlarged the conjugation, thus enhanced the light-harvesting ability and hole mobility, while further significantly improving the device performance. Additionally, TPA-T-DPP was also used as the electron-acceptor material, and the best P3HT:TPA-T-DPP based device exhibited a very high open-circuit voltage (1.14 V), which was among the highest values reported for single-layered OSC devices.

White light from polymer light-emitting diodes: Utilization of fluorenone defects and exciplex

A white light polymer light-emitting diode was demonstrated with a double layer configuration: poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (poly-TPD) blended with poly(N-vinylcarbazole) as both hole-transporting layer and electron-blocking layer, blue-emissive poly(9,9-dihexylfluorene-alt-co-2,5-dioctyloxy-para-phenylene) (PDHFDOOP) blended with green-emissive poly[6,6′-bi-(9,9′-dihexylfluorene)-co-(9,9′-dihexylfluorene-3-thiophene-5′-yl)] as an emissive layer. By annealing the emissive layer at a relatively high temperature, fluorenone defects were generated into PDHFDOOP, which formed an exciplex with poly-TPD, as a red emitter. The devices exhibit a maximum brightness of ∼4800cd∕m2 and a maximum luminous efficiency of ∼3cd∕A. Moreover, the Commission Internationale de L’Eclairage coordinates of the emitted light is close to that of pure white light and is insensitive to the applied voltages.