yao Lu

Cooperative Plasmonic Effect of Ag and Au Nanoparticles on Enhancing Performance of Polymer Solar Cells

This article describes a cooperative plasmonic effect on improving the performance of polymer bulk heterojunction solar cells. When mixed Ag and Au nanoparticles are incorporated into the anode buffer layer, dual nanoparticles show superior behavior on enhancing light absorption in comparison with single nanoparticles, which led to the realization of a polymer solar cell with a power conversion efficiency of 8.67%, accounting for a 20% enhancement. The cooperative plasmonic effect aroused from dual resonance enhancement of two different nanoparticles. The idea was further unraveled by comparing Au nanorods with Au nanoparticles for solar cell application. Detailed studies shed light into the influence of plasmonic nanostructures on exciton generation, dissociation, and charge recombination and transport inside thin film devices.

Understanding Low Bandgap Polymer PTB7 and Optimizing Polymer Solar Cells Based on It

Solution processed single junction polymer solar cells (PSCs) have been developed from less than 1% power conversion efficiency (PCE) to beyond 9% PCE in the last decade. The significant efficiency improvement comes from progress in both rational design of donor polymers and innovation of device architectures. Among all the novel high efficient donor polymers, PTB7 stands out as the most widely used one for solar cell studies. Herein the recent development of PTB7 solar cells is reviewed. Detailed discussion of basic property, structure property relationship, morphology study, interfacial engineering, and inorganic nanomaterials incorporation is provided. Possible future directions for further increasing the performance of PTB7 solar cells are discussed.

High-performance ternary blend polymer solar cells involving both energy transfer and hole relay processes

The integration of multiple materials with complementary absorptions into a single junction device is regarded as an efficient way to enhance the power conversion efficiency (PCE) of organic solar cells (OSCs). However, because of increased complexity with one more component, only limited high-performance ternary systems have been demonstrated previously. Here we report an efficient ternary blend OSC with a PCE of 9.2%. We show that the third component can reduce surface trap densities in the ternary blend. Detailed studies unravel that the improved performance results from synergistic effects of enlarged open circuit voltage, suppressed trap-assisted recombination, enhanced light absorption, increased hole extraction, efficient energy transfer and better morphology. The working mechanism and high device performance demonstrate new insights and design guidelines for high-performance ternary blend solar cells and suggest that ternary structure is a promising platform to boost the efficiency of OSCs.

Synthesis and Photovoltaic Effect in Dithieno[2,3‐d:2′,3′‐d′]Benzo[1,2‐b:4,5‐b′]dithiophene‐Based Conjugated Polymers

The recent surge of enthusiasm in bulk-heterojunction (BHJ) organic photovoltaics (OPVs) is driven by their potential for fabricating fl exible and light-weight solar cells via facile, lowcost solution processing techniques. [ 1 ] New materials are crucial in order for OPVs to mature fully from research and development into cost effective products. The power conversion effi ciency (PCE) of large-area OPV solar cells is still inferior to the corresponding inorganic devices and should be continuously improved through major advances in new materials and enhancing our understanding of structure-property relationships. [ 2– 6 ]

The Role of N-Doped Multiwall Carbon Nanotubes in Achieving Highly Efficient Polymer Bulk Heterojunction Solar Cells

This paper reports an improved solar cell performance of 8.6% by incorporation of N-doped multiwall carbon nanotubes (N-MCNTs) into BHJ solar cells composed of PTB7 and PC71BM. It was demonstrated for the first time that incorporation of N-MCNTs leads to not only increased nanocrystallite sizes but also smaller phase-separated domain sizes of both PTB7 copolymers and PC71BM from X-ray scattering study. The results show that N-MCNTs could serve as both exciton dissociation centers and charge transfer channels. The enhanced charge dissociation probabilities and effective charge carrier lifetime in the active layer material offer evidence to support the conclusion that N-MCNTs facilitated charge separation and transport.

Dielectric Interface Effects on Surface Charge Accumulation and Collection towards High-Efficiency Organic Solar Cells

This paper reports the experimental studies on the effects of dielectric thin-film on surface-charge accumulation and collection by using capacitance-voltage (C-V) measurements under photoexcitation. The dielectric thin-films with different surface polarizations are used with inverted device architecture based on the common photovoltaic PTB7:PC71BM film. In the C-V measurements, the peak-voltage shift with light intensity, namely, Vpeak shift, is particularly used to determine the surface-charge accumulation. We find that the Vpeak shows a smaller shift with light intensity when a higher surface polarization of dielectric thin-film is used. This means that a higher surface polarization of dielectric thin-film can decrease the surface-charge accumulation at electrode interface. However, a lower surface polarization of dielectric thin-film leads to a larger shift with light intensity. This implies that a lower surface polarization of dielectric thin-film corresponds to a larger surface-charge accumulation. ...

Optical properties of low bandgap copolymer PTB7 for organic photovoltaic applications

We used both cw and transient spectroscopies for studying the optical properties and photoexcitations in the low bandgap copolymer PTB7 that has been used in organic photovoltaic applications (OPV). Surprisingly we observed two primary photoexcitations that are generated within ~150 fs (our time resolution); we identify them as singlet exciton (S1) and triplet-pair (1TT). The singlet exciton has been considered to be the only primary photoexcitation in regular π-conjugated polymers and is related with a transient absorption band that peaks at an energy value close to the exciton binding energy (~0.4 eV in PTB7). The TT pair is a novel photoexcitation species in low band-gap π-conjugated copolymers. It has an absorption band close to that of isolated triplet exciton, and may readily dissociate at the donoracceptor interfaces in the PTB7/fullerene blend. This finding may explain the underlying mechanism for the high obtained power conversion efficiency in OPV devices based on the PTB7 copolymer.