RESUMEN
Hybrid organic-inorganic materials are a new class of materials used as interfacial layers (ILs) in polymer solar cells (PSCs). A hybrid material, composed of antimony as the inorganic part and diaminopyridine as the organic part, is synthesized and described as a new material for application as the electron extraction layer (EEL) in PSCs and compared to the recently demonstrated hybrid materials using bismuth instead of antimony. The hybrid compound is solution-processed onto the photoactive layer based on a classical blend, which is composed of a PTB7-Th low band gap polymer as the donor mixed with PC70BM fullerene as the acceptor material. By using a regular device structure and an aluminum cathode, the solar cells exhibited a power conversion efficiency of 8.42%, equivalent to the reference device using ZnO nanocrystals as the IL, and strongly improved compared to the bismuth-based hybrid material. The processing of extraction layers up to a thickness of 80 nm of such hybrid material reveals that the change from bismuth to antimony has strongly improved the charge extraction and transport properties of the hybrid materials. Interestingly, nanocomposites made of the hybrid material mixed with ZnO nanocrystals in a 1:1 ratio further improved the electronic properties of the extraction layers, leading to a power conversion efficiency of 9.74%. This was addressed to a more closely packed morphology of the hybrid layer, leading to further improved electron extraction. It is important to note that these hybrid EELs, both pure and ZnO-doped, also greatly improved the stability of solar cells, both under dark storage in air and under lighting under an inert atmosphere compared to solar cells treated with ZnO intermediate layers.
RESUMEN
Plasmonic nanocomposites based on well-dispersed silver nanocubes in poly(vinylpyrrolidone) are presented that are solution-processed into layers of varying volume fractions of nanocubes. We show that the high-energy modes of the nanocubes are almost insensitive to plasmonic coupling within the nanocube assemblies, leading to a linear increase in light absorption in the UV region with the nanocube densities. Concerning the main dipolar resonance mode at 450 nm, it is strongly affected by the formation of these assemblies, leading to an increased absorption in the UV region as well as a large absorption band in the visible region. Simulations of the optical response of the nanocube assemblies as a function of nanocube spacing and electric field polarization reveal that optical features in the visible region are due to intercube couplings at short intercube distances and parallel electric field orientation. In contrast, the additional plasmonic band in the UV region has its origin in residual dipolar oscillations of the nanocubes in combination with weak dipolar coupling for both parallel and transversal field polarizations. The combination of these effects leads to an enlarged absorption band in the UV region with nearly perfect light absorption of 98.8% at a high silver volume fraction of 8% that is accompanied by a very weak specular reflection of only 0.28%. Although such perfect absorption is usually observed only when nanocubes are assembled on a gold surface, nearly perfect absorption herein is achieved on a large palette of substrates including glass, plastic, and cheap metals such as aluminum, making it a promising approach for solution-processed robust and cheap quasi-perfect absorption coatings.
RESUMEN
Organic-inorganic hybrid materials composed of bismuth and diaminopyridine are studied as novel materials for electron extraction layers in polymer solar cells using regular device structures. The hybrid materials are solution processed on top of two different low band gap polymers (PTB7 or PTB7-Th) as donor materials mixed with fullerene PC70BM as the acceptor. The intercalation of the hybrid layer between the photoactive layer and the aluminum cathode leads to solar cells with a power conversion efficiency of 7.8% because of significant improvements in all photovoltaic parameters, that is, short-circuit current density, fill factor, and open-circuit voltage, similar to the reference devices using ZnO as the interfacial layer. However when using thick layers of such hybrid materials for electron extraction, only small losses in photocurrent density are observed in contrast to the reference material ZnO of pronounced losses because of optical spacer effects. Importantly, these hybrid electron extraction layers also strongly improve the device stability in air compared with solar cells processed with ZnO interlayers. Both results underline the high potential of this new class of hybrid materials as electron extraction materials toward robust processing of air stable organic solar cells.
RESUMEN
This work is focused on the study of the optical properties of silver nanostructures embedded in a polymer host matrix. The introduction of silver nanostructures in polymer thin films is assumed to result in layers having adaptable optical properties. Thin film layers with inclusions of differently shaped nanoparticles, such as nanospheres and nanoprisms, and of different sizes, are optically characterized. The nanoparticles are produced by a simple chemical synthesis at room temperature in water. The plasmonic resonance peaks of the different colloidal solutions range from 390 to 1300 nm. The non-absorbing, transparent polymer matrix poly(vinylpyrrolidone) (PVP) was chosen because of its suitable optical and chemical properties. The optical studies of the layers include spectrophotometry and spectroscopic ellipsometry measurements, which provide information about the reflection, transmission, absorption of the material as well as the complex optical indices, n and k. Finite difference time domain simulations of nanoparticles in thin film layers allow the visualization of the nanoparticle interactions or the electric field enhancement on and around the nanoparticles to complete the optical characterization. A simple analysis method is proposed to obtain the complex refractive index of nanospheres and nanoprisms in a polymer matrix.