Chen Weijie

Publication date: 16 January 2019

Source: Joule, Volume 3, Issue 1

Author(s): Xiaoyan Du, Thomas Heumueller, Wolfgang Gruber, Andrej Classen, Tobias Unruh, Ning Li, Christoph J. Brabec

Context & Scale

Summary

Graphical Abstract

The effect of grain cluster size on back‐contact perovskite solar cells is investigated. It is found that the photovoltaic performance correlates positively with the perovskite grain cluster size. This is attributed to the reduced charge recombination and more efficient charge injection accompany perovskite films with larger grains.

Abstract

Incorporating interdigitated back‐contact electrodes into organic–inorganic halide perovskite solar cells overcomes the optical losses and low architectural defect tolerance present in conventional “sandwich” cell configurations. However, other factors limit device performance in back‐contact architectures, such as the short charge‐carrier diffusion length within the perovskite film relative to the electrode spacing. As charge‐carrier diffusion length is crystal‐size related, in order to understand the effect of perovskite morphology on the performance of back‐contact perovskite solar cells (bc‐PSCs), perovskite films with four different grain cluster sizes, i.e., large, medium, small, and extra small, are fabricated via a solvent annealing approach. Crystallization of the perovskite is found to be closely related to the surface chemistry and topography of the substrate. The bc‐PSC photovoltaic performance correlates positively with the perovskite grain cluster size. Through a detailed analysis of transient photovoltage decay measurements, time‐resolved photoluminescence, and space charge‐limited current measurements, the effect of defect densities associated with grain cluster boundaries is elucidated.

Graphene‐based solar cells and photodetectors (PDs) have received burgeoning exploration. The Fermi level of graphene can be dynamically tuned by coating quantum dots (QDs), where optical absorption of graphene can also be decided by specified kind of QDs. The fundamental physical interaction between QDs and graphene is addressed and summarized. The applications of QDs/graphene‐based PDs and solar cells are highly expected.

Abstract

Graphene with a series of neoteric electronic and optical properties is an intriguing building block for optoelectronic devices. Over the past decade, graphene‐based solar cells (SCs) and photodetectors (PDs) which can convert light signals to electrical signals have received burgeoning exploration. However, limited light absorption hampers the performance of these devices. Quantum dots (QDs) possess a strong confinement effect, a large exciton energy, and long exciton lifetime, enhancing the interaction between incident light and graphene. Especially, as the density of states near the Dirac point of graphene is ultralow, it is easy to modify the Fermi level of graphene by inserting quantum dots at the interface between graphene and light, thereby enhancing the performance of graphene‐based optoelectronic devices. The characteristics of QDs and crucial physical mechanisms of the interaction and energy transfer in QDs/graphene nanohybrids are systematically addressed. The factors influencing the efficiency of energy transfer are also analyzed quantitatively. Moreover, the experimental process of QD‐enhanced technologies for SCs, photoconductors, phototransistors, and photodiode PDs is reviewed. Eventually, a conclusion is given and the remaining challenges and future development for QDs/2D materials hybrid systems is discussed. Possible steps toward large‐scale commercial applications and integration into optoelectronic networks are suggested.

A nonfullerene semitransparent tandem organic solar cell is fabricated by combining a medium‐bandgap photoactive layer based on P3TEA:FTTB‐PDI₄ and a narrow‐bandgap PTB7‐Th:IEICS‐4F blend as front and back subcells, respectively. As a result of matching current generation, a high efficiency of 10.5% is realized with a decent average transmittance of 20%.

Abstract

Semitransparent organic solar cells have great potential for building integrated photovoltaics and power‐generating windows owing to their advantages of light weight, mechanical flexibility, and color tunability. However, the performance of previous semitransparent organic solar cells have been limited by their relatively weak optical absorptions. In this paper, an efficient nonfullerene semitransparent tandem organic solar cell that exhibits a broad absorption from 300 to 1000 nm is reported. The rear subcell is based on a narrow‐bandgap nonfullerene acceptor named IEICS‐4F that exhibits a strong crystallinity and high electron mobility. As a result, the IEICS‐4F‐based single‐junction opaque and semitransparent organic solar cells yield high efficiencies of 10.3% and 7.5%, respectively. To further enhance light harvesting of the single‐junction semitransparent organic solar cells while maintaining a decent transmittance, a semitransparent tandem organic solar cell is fabricated by incorporating a medium‐bandgap P3TEA:FTTB‐PDI₄ blend as the front subcell. A high efficiency of 10.5% is recorded with an average transmittance of 20%.

Unique J‐architecture from a new fused ring–based nonfullerene acceptor is demonstrated. The well correlations between the single crystal data and the graze‐incidence X‐ray diffraction (GIXRD) data give a clear picture of the acceptor molecule packing in the donor:acceptor blend films and the assignments of the well often used GIXRD signals. A power conversion efficiency of 10.5% is obtained.

Abstract

An interesting and important question emerges with the rapid advances of the highly efficient fused‐ring nonfullerene acceptors; that is, how the acceptor molecules form aggregates in its blended film with a donor polymer/small molecule so as to offer highly efficient exciton diffusion and electron transport? To answer this question, a new acceptor molecule, 3,9‐bis(5‐methylene‐4‐one‐6‐(1,1‐dicyanomethylene)‐cyclopenta[c]thiophen‐2,8‐dimethyl)‐5,5,11,11‐tetrakis(4‐n‐hexylphenyl)‐dithieno[2,3‐d:2′,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene (ITCT‐DM), is designed and synthesized herein and its unique interpenetrating J‐architecture is presented in which the acceptor molecules form compacted and displaced ππ‐stacks with the distances of 3.1−4.2 Ǻ. Again the crystal structure data are correlated with the grazing‐incidence X‐ray diffraction (GIXRD) data of the pure acceptor and its polymer:acceptor blended films, which gives a clearer picture about the origins of the acceptor's GIXRD signals in both the pure and its blended films. Again, these results unveil the key roles of the uses of 1,8‐diiodooctane (DIO) and thermal annealing treatment in optimizing the acceptor phase morphologies in the donor:acceptor blended film, and the combination of the thermal annealing and DIO treatment leads to obtain higher crystallinity for both the donor and acceptor phases, more compacted packing, and finer morphologies. A power conversion efficiency of 10.5% is obtained.

A novel concept for the formation of the hole selective layer in efficient perovskite solar cells is presented. Carbazole‐based material is synthesized and used for the formation of a self‐assembled monolayer on top of the indium tin oxide transparent conductive substrate. Power conversion efficiency as high as 17.8% is achieved.

Abstract

The unprecedented emergence of perovskite‐based solar cells (PSCs) has been accompanied by an intensive search of suitable materials for charge‐selective contacts. For the first time a hole‐transporting self‐assembled monolayer (SAM) as the dopant‐free hole‐selective contact in p–i–n PSCs is used and a power conversion efficiency of up to 17.8% with average fill factor close to 80% and undetectable parasitic absorption is demonstrated. SAM formation is achieved by simply immersing the substrate into a solution of a novel molecule V1036 that binds to the indium tin oxide surface due to its phosphonic anchoring group. The SAM and its modifications are further characterized by Fourier‐transform infrared and vibrational sum‐frequency generation spectroscopy. In addition, photoelectron spectroscopy in air is used for measuring the ionization potential of the studied SAMs. This novel approach is also suitable for achieving a conformal coverage of large‐area and/or textured substrates with minimal material consumption and can potentially be extended to serve as a model system for substrate‐based perovskite nucleation and passivation control. Further gains in efficiency can be expected upon SAM optimization by means of molecular and compositional engineering.

In-situ cross-linking strategy for efficient and operationally stable methylammoniun lead iodide solar cells

In-situ cross-linking strategy for efficient and operationally stable methylammoniun lead iodide solar cells, Published online: 18 September 2018; doi:10.1038/s41467-018-06204-2

Graphdiyne‐ZnO composite material is prepared via a simple method and studied in detail. Zn and O atoms can coordinate bonding with graphdiyne, thus forming the CZn bond and CO bond, respectively, which improves the morphology and electrical conductivity of the interfacial layer. Polymer solar cells based on the nanocomposites obtain an enhanced power conversion efficiency of 11.2% compared with the devices with ZnO‐only (10%).

Graphdiyne‐ZnO (GDZO) composite material is prepared via a simple method and studied in detail for the first time. The transmission electron microscopy, Raman spectroscopy and X‐ray photoelectron spectroscopy (XPS) analyses confirm the formation of an adduct between GD and ZnO. Then the interaction between ZnO and GD is further investigated by first‐principles calculations. It is found that the Zn and O atom can coordinate bonding with GD, thus forming the CZn bond and CO bond, respectively. Polymer solar cells are fabricated based on the nanocomposites for the first time and an enhanced power conversion efficiency of 11.2%, compared with the devices with ZnO‐only (10%), is obtained. Simultaneously, the resultant devices show better stability, whether in glove box or in atmosphere, with humidity of 90%. The investigation of exciton generation rate, ideal current‐voltage model, and impedance spectra verify that the introduction of GDZO not only accelerates electron transfer but also reduces charge recombination occurring at the interface. The results indicate that GDZO is a promising electron transport material to enhance solar cell performance and presents a large potential for optoelectronic applications as well.