George Kakavelakis

Hellenic Mediterranean University · Department of Electronics Engineering

The electronic and material properties of graphene have been explored in a number of electronic and optoelectronic devices among them the organic and metal – halide perovskite solar cells. At present, graphene based technology is considered to have the greatest potentialities for applications. More over graphene related materials offer graphene cha...

Solution-processed organic–inorganic lead halide perovskite solar cells (PSCs) are considered as one of the most promising photovoltaic technologies thanks to both high performance and low manufacturing cost. However, a key challenge of this technology is the lack of ambient stability over prolonged solar irradiation under continuous operating cond...

Organic-inorganic lead halide based perovskite solar cells are considered as one of the most promising third generation photovoltaic technologies, since within a few years of focused research efforts, have already presented certified efficiencies overcoming 22%. The high performance together with the low fabrication cost, make this technology compe...

The development of large-scale production methods of two-dimensional (2D) crystals, with on-demand control of the area and thickness, is mandatory to fulfill the potential applications of such nanomaterials for photovoltaics. Inverted bulk heterojunction (BHJ) organic solar cell (OSC), that exploits a polymer-fullerene binary blend as the active ma...

Reduced graphene oxide (rGO) is added in the [6,6]-Phenyl-C61-butyric acid methyl ester (PCBM) electron transport layer (ETL) of planar inverted perovskite solar cells (PSCs), resulting in a power conversion efficiency (PCE) improvement of ≈12%, with a hysteresis-free PCE of 14.5%, compared to 12.9% for the pristine PCBM based device. The universal...

Ultrathin, solution-processed emerging solar cells with high power-per-weight (PPW) outputs demonstrate unique potential for applications where low weight, high power output, and flexibility are indispensable. The following perspective explores the literature of emerging PVs and highlights the maximum reported PPW values of perovskite solar cells (...

Heating adversely affects solar cells performance and reliability. Here, we propose a transparent multispectral photonic electrode placed on top of the glass substrate of solar cells, which simultaneously reduces the device solar heating and enhances its efficiency. Specifically, the proposed photonic electrode, composed of a low resistivity metal...

Ultrathin, solution-processed emerging solar cells with high power-per-weight (PPW) outputs demonstrate unique potential for applications where low weight, high power output, and flexibility are indispensable. The following perspective explores the literature of emerging PVs and highlights the maximum reported PPW values of Perovskite Solar Cells (...

Layered material heterostructures (LMHs) can be used to fabricate electroluminescent devices operating in the visible spectral region. A major advantage of LMH-light emitting diodes (LEDs) is that electroluminescence (EL) emission can be tuned across that of different exciton complexes (e.g. biexcitons, trions, quintons) by controlling the charge d...

Metal halide perovskites (MHPs) have shown an incredible rise in efficiency, reaching as high as 25.7%, which now competes with traditional photovoltaic technologies. Herein, we excluded CsX and RbX, the most commonly used cations to stabilize FAPbI3, from the bulk of perovskite thin films and applied them on the surface, as passivation agents. Ext...

Although it has been recently demonstrated that the laser-assisted (LA) crystallization process leads to the formation of perovskite absorber films of superior photovoltaic performance compared to conventional thermal annealing (TA), the physical origin behind this important discovery is missing. In this study, CH$_3$NH$_3$PbI$_3$ perovskite thin f...

Metal halide perovskites (MHPs) have emerged as a frontrunner semiconductor technology for application in third generation photovoltaics while simultaneously making significant strides in other areas of optoelectronics. Photodetectors are one of the latest additions in an expanding list of applications of this fascinating family of materials. The e...

Hydrogen (H2) is a well-known reduction gas and for safety reasons is very important to be detected. The most common systems employed along its detection are metal oxide-based elements. However, the latter demand complex and expensive manufacturing techniques, while they also need high temperatures orUVlight to operate effectively. In this work, we...

Solution-processed, lead halide-based perovskite solar cells have recently overcome important challenges, offering low-cost and high solar power conversion efficiencies. However, they still undergo unoptimized light collection due mainly to the thin (∼350 nm) polycrystalline absorber layers. Moreover, their high toxicity (due to the presence of lea...

Hydrogen (H2) is a well-known reduction gas and for safety reasons is very important to be detected. The most common systems employed along its detection are metal oxide-based elements. However, the latter demand complex and expensive manufacturing techniques, while they also need high temperatures or UV light to operate effectively. In this work,...

The construction of low cost, printable compatible, solution processed, of high performance, stable solar cells is one of the scientific milestones of the next ten years. The discovery of graphene launched a new era in the materials science, and the research implemented in the exceptional properties of the two-dimensional (2D) materials. The chemic...

Solution-processed, lead halide-based perovskite solar cells have overcome important challenges over the recent years, offering low-cost and high solar power conversion efficiencies. However, they still undergo unoptimized light collection due mainly to the thin (~350 nm) polycrystalline absorber layers. Moreover, their high toxicity (due to the pr...

Inorganic and organic-inorganic (hybrid) perovskite semiconductor materials have attracted worldwide scientific attention and research effort as the new wonder semiconductor material in optoelectronics. Their excellent physical and electronic properties have been exploited to boost the solar cells efficiency beyond 23% and captivate their potential...

Inorganic and organic – inorganic (hybrid) perovskite semiconductor materials have attracted the worldwide scientific attention and research effort as the new wonder material in optoelectronics. Their excellent physical and electronic properties have been exploited to boost the solar cells efficiency beyond 23% and captivate their potential as comp...

Although it has been recently demonstrated that the laser-assisted (LA) crystallization process leads to the formation of perovskite absorber films of superior photovoltaic performance compared to conventional thermal annealing (TA), the physical origin behind this important discovery is missing. In this study, CH3NH3PbI3 perovskite thin films have...

This work is part of the interlaboratory collaboration to study the stability of organic solar cells containing PCDTBT polymer as a donor material. The varieties of the OPV devices with different device architectures, electrode materials, encapsulation, and device dimensions were prepared by seven research laboratories. Sets of identical devices we...

Stability of organic solar cells with PCDTBT donor polymer: An interlaboratory study – ERRATUM - Laura Ciammaruchi, Ricardo Oliveira, Ana Charas, Tulus, Elizabeth von Hauff, Giuseppina Polino, Francesca Brunetti, Rickard Hansson, Ellen Moons, Miron Krassas, George Kakavelakis, Emmanuel Kymakis, José G. Sánchez, Josep Ferre-Borrull, Lluis F. Marsal,...

In this Research News, the authors summarize the work that has been done on the utilization of 2D materials beyond graphene in the electron transport layer (ETL) and hole transport layer (HTL) selected of metal halide perovskite solar cells (PSCs). On the one hand, the impact of such materials in the stability of PSCs under operational conditions i...

Metal halide based perovskite solar cells are considered among the most promising photovoltaic technologies already presenting certified efficiencies surpassing 22%. The high performance and the low fabrication cost, makes this technology competitive with state-of-the-art thin film photovoltaics. However perovskite solar cells present some striking...

Hybrid lead halide spin coated perovskite films have been successfully tested as portable, flexible, operated at room temperature, self-powered and ultra-sensitive ozone sensing elements. The electrical resistance of the hybrid lead mixed halide perovskite (CH3NH3PbI3−xClx) sensing element, was immediately decreased when exposed to an ozone (O3) en...

CH3NH3PbI3 perovskite thin films have been deposited on glass/indium tin oxide (ITO)/Hole Transport Layer (HTL) substrates, utilizing two different materials as the HTLs. In the first configuration the super hydrophilic polymer poly (3,4-ethylenedioxythiophene)-poly (styrenesulfonate), known as PEDOT:PSS, was employed as the HTL material, while on...

The systematic optimization of the chemical structure of low-bandgap (LBG) donor-acceptor polymeric semiconductors is a challenging task for which accurate guidelines are yet to be determined. Several different structural and molecular parameters are crucial ingredients for obtaining LBG polymers that simultaneously possess high power conversion ef...

Recently, the study of ternary organic solar cells (OSCs) has attracted the efforts of the scientific community, leading to significantly higher performance due to the enhanced harvesting of incoming irradiation. Here, for the first time, and in order to promote this OSC architecture, we review the progress implemented by the application of two-dim...

In this work, the addition of different types (Au, Ag and Al) of metal nanoparticles (NPs) in the PEDOT:PSS hole transport layer of inverted perovskite solar cells was systematically studied. The Ag and Au NP incorporation led to the highest power conversion efficiency improvement, while the Al NP-based devices showed significantly improved stabili...

Interfaces between perovskite solar cell (PSC) layer components play a pivotal role in obtaining high-performance premium cells and large-area modules. Graphene and related two-dimensional materials (GRMs) can be used to “on-demand” tune the interface properties of PSCs. We successfully used GRMs to realize large-area (active area 50.6 cm2) perovsk...

Since the isolation of free standing graphene in 2004, graphene research has experienced a phenomenal growth. Due to its exceptional electronic, optical and mechanical properties, it is believed to be the next wonder material for optoelectronics. The enhanced electrical conductivity, combined with its high transparency in visible and near-infrared...

This work proposes a new perovskite solar cell structure by including lithium-neutralized graphene oxide (GO-Li) as the electron transporting layer (ETL) on top of the mesoporous TiO2 (m-TiO2) substrate. The modified work-function of GO after the intercalation of Li atoms (4.3 eV) exhibits a good energy matching with the TiO2 conduction band, leadi...

A new light trapping architecture to enhance the power conversion efficiency of organic photovoltaics is proposed and implemented. In article number 1501640, Emmanuel Kymakis and co-workers demonstrate that the incorporation of gold nanorods inside the rear buffer layer, leads to the redistribution of photons inside the active medium mainly through...

The effective utilization of work-function (WF) tuned solution processable graphene-based derivatives as both hole and electron transport layers in organic photovoltaic (OPV) devices is demonstrated. The systematic tuning of the functionalized graphene oxide (GO) WF took place by either photochlorination for WF increase, or lithium neutralization f...

A powerful insight into the structural and interfacial properties of post-fabricated bulk heterojunction (BHJ) organic photovoltaic (OPV) devices is reported. The nanoscale local structure of integrated devices is revealed by combined X-ray diffraction (XRD) and fluorescence (XRF) investigations. A comparative study is performed on devices using gr...

A graphene-based porphyrin molecule (GO-TPP) was synthesized by covalent linkage of graphene oxide (GO) with 5-(4-aminophenyl)-10,15,20-triphenyl porphyrin (TPP-NH2). The yielded graphene-based material is a donor-acceptor (D-A) molecule, exhibiting strong intermolecular interactions between the GO core (A) and the covalently anchored porphyrin mol...

The effects of incorporating uncapped aluminum (Al) nanoparticles (NPs), fabricated by laser ablation in liquid, in the hole transport layer (HTL) of organic photovoltaic devices were systematically investigated. The integration of Al NPs in the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hole transport layer resulted in 8.7...

There has been a lot of interest regarding the influence of active-layer-incorporated plasmonic nanoparticles (NPs) in the performance of bulk heterojunction organic photovoltaic (OPV) devices, while both an increase and decrease in performance have been reported. In this paper, following a systematic approach, we demonstrate strong evidence of the...

A laser-based patterning technique—compatible with flexible, temperature-sensitive substrates—for the production of large area reduced graphene oxide micromesh (rGOMM) electrodes is presented. The mesh patterning can be accurately controlled in order to significantly enhance the electrode transparency, with a subsequent slight increase in the sheet...

A photochemical route for the facile synthesis of tunable bandgap graphene- based derivatives from graphene oxide (GO) through controlled laser irradiation in liquid phase is presented. The method is facile and fast, yielding these materials within 2 h and with excellent long-term stability. It makes use of photogenerated-solvated electrons that gi...

Lithium-neutralized graphene oxide (GO-Li) was spin coated between the photoactive layer and the metal oxide electron-transporting layer (ETL) as an additional interlayer in organic photovoltaic devices. The introduction of GO-Li leads to a superior interface between the ETL and the photoactive layer. Combined with the reduced work function (WF) of...

Enhancement in the efficiency of air processed bulk heterojunction photovoltaic devices is demonstrated via the addition of highly stable uncapped gold (Au) and aluminum (Al) nanoparticles (NPs) into the photoactive layer. An enhancement in conversion efficiency by 15% is observed, which can be attributed to Localised Surface Plasmon Resonance effe...

Enhancement of both the efficiency and stability of bulk heterojunction photovoltaic devices is demonstrated by the addition of highly stable Al NPs, generated via laser ablation, into the photoactive layer. An efficiency enhancement of 30% is demonstrated, which can be attributed to multiple scattering effects and enhanced structural stability of...

Enhancement of both the efficiency and stability of bulk heterojunction photovoltaic devices is demonstrated by the addition of highly stable Al NPs, generated via laser ablation, into the photoactive layer. An efficiency enhancement of 30% is demonstrated, which can be attributed to multiple scattering effects and enhanced structural stability of...