Dr Apostolos Panagiotopoulos

The complex and varied relationship found in intermolecular interactions within the photo-active layers play a decisive role in determining photovoltaic energy conversion and overall device performance of organic solar cells (OSCs). Among different approaches, the ternary blend strategy serves as an effective technique to control the morphology within the active layer in OSCs. In this work, PM6:L8-BO is used as the main host system (binary) while the fullerene molecules PC61BM and PCBC6 are introduced to form ternary OSCs. The results highlight the important role of fullerenes to enhance the performance of binary non-fullerene acceptor-based cells by suppressing trap-assisted recombination and optimizing the active layer morphology. The improved film phase microstructure, enabled by fullerene derivatives with higher lowest unoccupied molecular orbital (LUMO) energy levels in comparison to the host acceptor (L8-BO), facilitates more efficient charge collection and reduced non-radiative recombination. This results in an increase in the fill factor (FF) and open circuit voltage (Voc) in the ternary OSCs. Consequently, power conversion efficiencies (PCEs) of binary OSCs were increased from 17.28% to 18.10% and 18.38% for the PC61BM- and PCBC6-based ternary OSCs, respectively. Furthermore, the addition of the fullerene molecules in the active layer provided the devices with enhanced long-term photo and thermal stability. The ternary OSCs demonstrated degradation pathways distinct to those of binary cells (ISOS-L1-I and ISOS-D2-I protocols), as identified through in-situ ultraviolet-visible (UV-Vis) absorption and Raman spectroscopy. Molecular dynamics (MD) simulations, for the first time, reveal the significant role of fullerene molecules as morphology regulators in non-fullerene acceptor (NFA)-based systems. Their presence ensures improved dispersion of blend components and promotes more uniform and isotropic thermal and mechanical behaviour. Finally, mini-modules with active areas of 3.8 cm² were fabricated, achieving PCEs of 12.90%, 13.32%, and 13.70% for the binary and ternary cells using PC61BM-and PCBC6-based ternary cells, respectively. Our results demonstrate that regulating the morphological of the photo-active layer in OSCs through fullerene incorporation reduces the non-radiative energy loss pathways, enabling high-efficiency, stable and scalable OSCs.

Although methylammonium lead iodide (CH 3 NH 3 PbI 3 ) perovskite has attracted enormous scientific attention over the last decade or so, important information on the charge extraction dynamics and recombination processes in perovskite devices is still missing. Herein we present a novel approach to evaluate the quality of CH 3 NH 3 PbI 3 layers, via in situ monitoring of the perovskite layer charge carrier dynamics during the thermal annealing crystallization process, by means of time-resolved femtosecond transient absorption spectroscopy (TAS). In particular, CH 3 NH 3 PbI 3 films were deposited on two types of polymeric hole transport layers (HTL), poly(3,4-ethylenedioxythiophene)-poly-(styrenesulfonate) (PEDOT:PSS) and poly-(triarylamine) (PTAA), that are known to provide different carrier transport characteristics in perovskite solar cells. In order to monitor the evolution of the perovskite charge carrier dynamics during the crystallization process, the so-formed CH 3 NH 3 PbI 3 /HTL architectures were studied in situ by TAS at three different annealing temperatures, i.e. , 90, 100 and 110 °C. It is revealed that the annealing time period required in order to achieve the optimum perovskite film quality in terms of the decay dynamics strongly depends on the annealing temperature, as well as, on the employed HTL. For both HTLs, the required period decreases as higher annealing temperature is used, while, for the more hydrophobic PTAA polymer, longer annealing periods were required in order to obtain the optimum charge carrier dynamics. The correlation of the TAS finding with the structural and morphological features of the perovskite films is analysed and provides useful insights on the charge extraction dynamics and recombination processes in perovskite optoelectronic devices.

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 as competitors to the dominant silicon solar cells technology. However, the fundamental principles in Physics, dictate that an excellent direct band gap material for photovoltaic applications must be also an excellent light emitter candidate. This has been realized for the case of perovskite-based light emitting diodes (LEDs) but much less for the case of the respective laser devices. Here, the strides, exclusively in lasing, made since 2014 are presented for the first time. The solution processability, low temperature crystallization, formation of nearly defect free, nanostructures, the long range ambipolar transport, the direct energy band gap, the high spectral emission tunability over the entire visible spectrum and the almost 100% external luminescence efficiency show perovskite semiconductors' potential to transform the nanophotonics sector. The operational principles, the various adopted material and laser configurations along the future challenges are reviewed and presented in this paper.

The application of ultraviolet ozone (UV-Ozone) treatment of thermally evaporated molybdenum oxide (MoOx) as a hole transport layer (HTL) in non-fullerene acceptor (NFA)-organic solar cells (OSCs) has markedly improved the charge carrier transport. As a result, we report the power conversion efficiency (PCE) of PM6:Y6-based OSCs has been improved from 14.26% for pristine to 15.06% for UV-Ozone-treated devices. This PCE enhancement is attributed to increased hole mobility, more balanced mobilities ratio and higher direct current (DC) conductivity. Additionally, the formation of a more favourable interface between MoOx and the PM6:Y6 due to the UV-Ozone exposure, resulted in longer charge carrier lifetimes. Light soaking experiments at 55 degrees C in a nitrogen environment demonstrated superior operational stability with pristine and UV-Ozone-treated MoOx, retaining 58% and 65% of their initial PCE after 100 hours, respectively. This stands in contrast to devices based on PEDOT:PSS that deteriorated to 23% of their initial PCE after half the time period. This strategy is an enabler towards simultaneous improvement in performance and stability compared to the control PEDOT:PSS-based cells, presenting high efficiency but significantly lower lifetime stability. The broad applicability of UV-Ozone treatment of thermally evaporated MoOx HTLs was further validated through the fabrication of OSCs with a PM6:L8-BO photoactive layer, achieving a peak PCE value of 16.85%. These findings indicate significant advancements in the use of transition metal oxides in NFA-based OSCs and highlight the potential for new device architectures for organic electronics.

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, we first report a solution processed hybrid mixed halide spin coated perovskite films (CH3NH3PbI3−xClx) that have been successfully applied as portable, flexible, self-powered, fast and sensitive hydrogen sensing elements, operating at room temperature. The minimum concentrations of H2 gas that could be detected was down to 10 ppm. This work provides a new pathway on gases interaction with perovskite materials, poses new questions that must be addressed regarding the sensing mechanisms involved. The utilization of halide perovskite sensing elements demonstrates their potential beyond solar cell applications.

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 extensive range of possible inorganic and hybrid perovskites coupled with their processing versatility and ability to convert external stimuli into easily measurable optical/electrical signals makes them an auspicious sensing element even for the high‐energy domain of the electromagnetic spectrum. Key to this is the ability of MHPs to accommodate heavy elements while being able to form large, high‐quality crystals and polycrystalline layers, making them one of the most promising emerging X‐ray and γ ‐ray detector technologies. Here, the fundamental principles of high‐energy radiation detection are reviewed with emphasis on recent progress in the emerging and fascinating field of metal halide perovskite‐based X‐ray and γ ‐ray detectors. The review starts with a discussion of the basic principles of high‐energy radiation detection with focus on key performance metrics followed by a comprehensive summary of the recent progress in the field of perovskite‐based detectors. The article concludes with a discussion of the remaining challenges and future perspectives. Metal halide perovskites have emerged as a promising family of electronic materials for application in optoelectronics. One area where scientific interest in these materials has been intensifying is high‐energy radiation detection. This review discusses the progress in the application of metal halide perovskites for direct & indirect X‐ray and Gamma‐ray detection.

Planar inverted lead halide photovoltaics demonstrate remarkable photoconversion properties when employing poly(triarylamine) (PTAA) as a hole transporting layer. Herein, we elucidate the effect of ambient ultraviolet (UV) degradation on the structural and operational stability of the PTAA hole transporter through a series of rigorous optoelectrical characterization protocols. Due attention was given to the interplay between the polymer and perovskite absorber, both within the framework of a bilayer structure and fully assembled solar cells. The obtained results imply that UV degradation exerts a major influence on the structural integrity of PTAA, rather than on the interface with the perovskite light harvester. Moreover, UV exposure induced more adverse effects on tested samples than environmental humidity and oxygen, contributing more to the overall reduction of charge extraction properties of PTAA, as well as increased defect population upon prolonged UV exposure. Operational stability and structural integrity of a poly(triarylamine) hole transporter and methylammonium lead halide absorber are investigated upon exposure to UV stress.

The urgency for a sustainable mitigation of the environmental impacts caused by climate change highlights the importance of renewable energy technologies to fight this challenge. Perovskite solar cells (PSCs) emerge as a promising alternative to traditional photovoltaic (PV) technologies due to their unprecedented increase in efficiency (currently peaking at 26.95%) and long-term stability proven by the successful completion of industry relevant International Electrotechnical Commission (IEC) testing standards. Flexible PSCs (f-PSCs) offer significant advantages such as lightweight and high power-per-weight ratio, mechanical flexibility, and a high throughput roll-to-roll (R2R) manufacturing. These make f-PSCs ideal for implementation in various applications areas, such as wearable electronics, portable devices, space PV, building- or automotive-integrated PVs, and more. Notably, efficiencies over 23% now mark a significant milestone for f-PSCs, demonstrating their competitiveness with traditional rigid solar panels. This review explores breakthroughs in f-PSCs, focusing on flexible substrates, electrode materials, perovskite inks, and encapsulation strategies. It also covers recent advancements and studies of f-PSCs fabricated by scalable deposition methods and emphasizes the importance of interfacial engineering and encapsulation in enhancing stability and durability. The review concludes with a summary of key findings, remaining challenges, and perspectives for the successful market uptake of f-PSCs.

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 (PSCs) 29.4 W/g, organic solar cells (OSCs) 32.07 W/g, and quantum dot solar cells 15.02 W/g, respectively. The record PPW values of OSCs and PSCs are approximately one order of magnitude higher compared to their inorganic ultrathin solar cells counterparts (approximately 3.2 W/g for CIGS and a-Si). This consists emerging PVs, very attractive for a variety of applications where the PPW is the key parameter. In particular, both OSCs and PSCs can be implemented in different scenarios of applications (indoor and biocompatible applications for OSCs and outdoor and high-energy radiation conversion conditions for the PSCs) due to their unique optoelectronic and physiochemical properties. Finally, our theoretical optical and electrical simulation and optimization study for the most promising and well-suited PV technologies showed an impressive maximum realistic theoretical PPW limit of 74.3 and 93.7 W/g for PSCs and OSCs, respectively. Our finding in the theoretical section shows that the experimental results achieved in the literature of PSCs and OSCs toward high PPW outputs is not quite close to the theoretical maximum (35% and 40% of the theoretical maximum for OSCs and PSCs, respectively), and thus, more work needs to be done to further increase the experimental PPW output of these promising PV technologies.

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 (PSCs) 29.4 W/g, Organic Solar Cells (OSCs) 32.07 W/g and Quantum Dot Solar Cells (QDSC) 15.02 W/g, respectively. The record PPW values of OSCs and PSCs are approximately one order of magnitude higher compared to their inorganic ultrathin solar cells counterparts (approx. 3.2 W/g for CIGS and a-Si). This consists emerging PVs, very attractive for a variety of applications where the PPW is the key parameter. In particular, both OSCs and PSCs can be implemented in different scenarios of applications (indoor and biocompatible applications for OSCs and outdoor and high-energy radiation conversion conditions for the PSCs) due to their unique optoelectronic and physiochemical properties. Finally, our theoretical optical and electrical simulation and optimization study for the most promising and well-suited PV technologies, showed an impressive maximum realistic theoretical PPW limit of 74.3 and 93.7 W/g for PSCs and OSCs, respectively. Our finding shows that the literature PSCs and OSCs towards high PPW outputs, is not quite close to the theoretical maximum and thus more work needs to be done to further increase the PPW output of these promising PV technologies.