This study explores the efficacy of solvent vapor annealing (SVA) in enhancing the performance of organic solar cells (OSCs) by mitigating charge recombination and improving charge extraction, which are prevalent issues limiting their efficiency. Focusing on an OSC blend with known suboptimal characteristics, we specifically examine the effects of SVA on the blend's morphology, optical properties, and charge dynamics. Notably, SVA treatment significantly increases the short-circuit current density (Jsc) from 17.24 +/- 1.66 mA cm-2 to 26.92 +/- 1.06 mA cm-2 for an optimal 30 s treatment. However, extended treatment durations inversely affect the Jsc, indicating the need for precise control of the SVA protocol. The treatment also induces shifts in the optical absorption spectra and morphological changes. The impact of improved optical properties on charge photogeneration was analyzed by transfer matrix method simulations, while transient absorption, transient photovoltage (TPV) and transient photocurrent measurements helped to understand the dynamics of charge recombination. Both features explain the increase in experimental cell performance. These findings bring light to the mechanisms behind the use of SVA to enhance OSC performance and underscore its potential by careful implementation of a simple post-processing technique.

Recent advances in donor and acceptor molecules have significantly enhanced the efficiency and competitiveness of organic solar cells. However, optimizing the interfaces remains a critical issue in increasing the photovoltaic performance, mainly to reduce charge accumulation between the hole transport layers (HTLs) and the active layer. In this work, the interface between PM6:Y6 (active layer) and PEDOT:PSS (HTL) has been modified with silver nanoparticles (AgNPs). These AgNPs have been synthesized in anhydrous chlorobenzene by laser ablation synthesis in solution (LASiS). The choice of chlorobenzene as the medium for the synthesis of NPs by LASiS allows direct deposition onto the HTL. Measurements performed using steady-state current-voltage (J-V), Photo-CELIV, and current/voltage transient (TPC/TPV) revealed enhanced and reproducible photovoltaic parameters. The AgNPs also improve the device stability and can also be used on top of other HTLs, such as Br-2PACz. Theoretical analyses were performed by fitting an analytical model to the experimental data of photocurrent, which showed that the AgNP layer reduced bimolecular recombination losses. These findings suggest that the AgNP-modified interface of the PEDOT:PSS/active layer is a promising and versatile strategy to optimize interfacial properties, thus minimizing recombination losses and enhancing the efficiency, reproducibility, and stability of organic solar cells.

A published theoretical approach for forecasting the photovoltaic behavior of D-A copolymers, relying on the frontier levels of donor-acceptor (D-A) type copolymer was tested experimentally. The pair [5,11-bis(2-ethylhexyl) dihydroindolo [3,2-b]-carbazole] (D)/[3,6-Bis(4-octylthiophen-2-yl)-1,2,4,5-tetrazine] (A) was chosen to prepare the DA copolymer (PIC-TTz), based on an extensive theoretical study that has considered 2080 DA possible combinations. The energy levels, estimated by cyclic voltammetry joined with absorption spectra revealed that the polymer have appropriate energy levels for organic photovoltaic application. Polymer photovoltaic devices based on blends of the copolymer and PC71BM showed a high open-circuit voltage (>0.9 V) under the illumination of AM 1.5 (100 mWcm(-2)). The determined power conversion efficiency (PCE) was 1.12 %, and this result is discussed in light of the photophysical behavior not considered in the theoretical approach. It was demonstrated that although promising, the theory can be used as a guide, but not enough to substitute bench work.

The increasing demand of renewable energy sources led researchers to investigate new materials and blends for energy generation and harvesting. In this context, the utilization of conjugated polymers has led to the development of optoelectronic devices that exhibit excellent response characteristics while remaining cost-effective and flexible. Moreover, blends can be produced in solution, using natural biopolymers aiming to produce electrodes for capacitors. For instance, the pseudocapacitive behavior of polyaniline (PANI) enables its application in high-power density supercapacitors. In this paper, PANI and Lignin blends were prepared and applied as an electrode in supercapacitors. Lignin, a naturally occurring biopolymer found in plants and commonly produced as a residue in the paper industry, was utilized in this study. The Lignin content was changed from 25 up to 75

Conjugated copolymers possess intriguing electronic characteristics that can be precisely modulated by manipulating their chemical structures. In this study, we explored two approaches for fine-tuning the energy levels of these copolymers: the incorporation of heterocyclic moieties between the donor and acceptor units, and the substitution of a chalcogen atom in the acceptor unit. Specifically, we investigated the insertion of a thiophene along the polymer backbone and the replacement of sulfur with selenium in the acceptor unit. A series of copolymers were synthesized and thoroughly characterized using both experimental and theoretical methods. Partial density distribution of states analysis revealed that the inclusion of a thiophene significantly altered the HOMO level. Furthermore, the resulting Eg exhibited a decrease of approximately 0.8-0.9 eV compared to the copolymer without thiophene, indicating an enhanced planarization of the chain and increased conjugation length. Experimental data obtained from cyclic voltammetry demonstrated that both the conjugation length and the chalcogen atom in the acceptor unit played crucial roles in controlling the energy levels of the HOMO and LUMO. These findings establish a clear correlation between the chemical structure and the properties of the copolymers, demonstrating the potential for precise control and tailoring of their electronic characteristics.

An overview is presented of experimental investigations during two decades at the Polymer Group Prof. Bernhard Gross in Sao Carlos, Brazil, on the properties of piezoelectric polymers. The paper is focused on innovations with the introduction of the constant current technique and corona triodes. Together with thermally stimulated depolarization and heat pulse techniques, the methods created in Sao Carlos were applied to characterize dielectric polymers whose piezoelectric and ferroelectric properties depended on polarization or space charge. Results on phase transitions and ferroelectric properties are described for polyvinylidene fluoride (PVDF) and its copolymers, with emphasis on the observation of metastable ferroelectric polarization. The precise characterization of ferroelectric-to-paraelectric phase transitions and the determination of the origin of piezoelectric activity required the combination of different techniques, which could only be done with the developments in instrumentation.

Spin coating has been the primary choice of deposition method used in the assembly of lab-scale perovskite solar cells. Other deposition methods are still lagging behind, both in terms of device efficiency and in the control of perovskite formation/morphology. Usually, improvements in these processes have been achieved with strategies that are not compatible with the industrial scale, either because of the use of hazardous solvents or due to the costly steps adopted. Here, we report the development of a route to prepare all layers of perovskite solar cells (except the electrodes) through the blade-coating technique, which is a scalable method and can be applied to produce large-area solar cells. We discuss how each process parameter affects the device performance and show that, by tuning the ink composition (i.e., solvent and lead precursors), it is possible to reduce the temperature of the deposition and achieve a perovskite layer with adequate grain size and good coverage of the substrate. With these modifications, a solar cell with a p-i-n configuration assembled in a dry air atmosphere with 15-20% humidity and using the blade coater at 50 degrees C delivered a maximum of 14.3% of efficiency.

We develop an analytical model for the photocurrent of organic solar cells based on carrier drift and including second-order charge recombination, in which the figure of merit theta(o) naturally appears. This approach provides expressions for the fill-factor-theta(o) and alpha-theta(o) relations, where a is the exponent of the function of the short-circuit current versus light intensity (J(SC) proportional to I-alpha). A correlation between the reduction factor of Langevin recombination and the dissociation probability of charge transfer states (P) is also discussed. Photocurrent curves of a polymer device obtained at different temperatures (100-300 K) are fitted by the model, whose fitting parameters are in agreement with the literature.

The goal of this work is to make a contribution to the complex subject of organic solar cells degradation when operating in contact with ambient air. For this we built solar cells of the bulk heterojunction type composed of PTB7-Th (poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yebenzo [1,2-b;4,5-b']dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno [3,4-b]thiophene)-2-carboxylate-2-6-diyl)]) and PC71BM ([6,6]-Phenyl-C71-butyric acid methyl ester), respectively, as donor and acceptor materials of electrons. We present a series of current-voltage curves (J-V), both in the dark and under illumination, initially with the device immersed in an inert atmosphere and then exposing it to the ambient environment. J-V curves is then analyzed in terms of the Mott-Gurney equation, for measurements in dark, and by an analytical expression for the photocurrent, which allow us to check how the charge carrier mobility and the non-geminate recombination coefficient vary with time of exposure to air. We conclude that the charge carrier mobility (mu) for cells made with the PTB7-Th:PC71BM blend varies very little when in contact with air, and similar influence is observed on the recombination coefficient (k), since the Langevin coefficient reduction factor (zeta) is about 0.2 when the device is in inert atmosphere, reaching a value of almost 0.9 when exposed to air for 43 h.

Polymer light-emitting electrochemical cells (PLECs) are organic electronic devices which operating mechanism depends on the injection and transport of electronic charge carrier and the electrochemical doping of the organic semiconductor. The details of the interactions between the salt (or its ions) and the semiconducting polymer composing the device active layer provide important information about the electronic processes associated to the device operation in steady-state. In this context, the present paper proposes a study where theoretical results from Density Functional Theory (DFT) were obtained for three different steady-state operational regimes: i) without external voltage, in which the undissociated salt molecules interact with uncharged semiconducting polymer; ii) for applied voltages lower than the device turn-on (VEg/e), in which the dissociated ions interact with charged semiconducting polymer. In addition, the theoretical results have been confronted with experimental results of PLECs fabricated using different salt concentrations. For both theoretical and experimental approaches, we considered lithium triflate as the salt compound and poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-vinylenephenylene)] (F8PV) as the semiconducting polymer. We observed substantial changes in the electronic structure of the systems at the different operating regimes, which were interpreted in terms of the electronic charge injection from the electrodes and the electrochemical doping of the semiconducting polymer.

The origin of capacitance peaks in C-V measurements often observed in organic thin-film diodes is still waiting for a definitive explanation. It has been reported that one of two-peak C-V detected in p-doped material based devices are caused by involuntary doping, while the second one is attributed to trapped carriers. In this study, we show a ITO/P3HT/Al diode exhibiting one C-V peak at approximately 0.48 V, in both non-exposed and air-exposed devices. The second peak, (around 1.5 V) arises when the device is exposed to air, and increases significantly with exposure time. We suggest that the second peak is originated by a volumetric p-doping of P3HT due to the action of oxygen and the formation of electrons deep traps. A simple model to explain the C-V experiments is presented and is in agreement with this hypothesis.

Much has been reported on the effects of air action on the physical entities related to the transport processes in organic solar cells, for example, the electronic mobility, the lifetime of the charge carriers and the recombination kinetics. These effects have a direct impact on the series and parallel resistances (Rs and Rsh) of the solar cell, but studies of the action of the air environment on these resistances have been little explored. Here we present an experimental study of the environment action on an ITO/PEDOT:PSS/PTB7-Th:PC71BM/Ca/Al device, exploring mainly the variation of the series and the shunt resistances with the air exposure time. We used the classical equation of the current–voltage of an equivalent circuit of a solar cell to fit the experimental results, and used Rs and Rsh as adjustment parameters. We also correlated these resistances with the fill factor by the help of an approach developed by M. A. Green in 1982.

We carried out synthesis of shape-controlled ZnO nanoparticles following a polyol route using either ethylene glycol (EG) or polyethylene glycol (PEG) as solvent, which exhibited wurtzite structures as identified by XRD patterns. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) analyses of the synthesized structures showed that the size and the shape are strongly dependent on the reaction medium, resulting in nanospheres, rods, hexagonal plates or sheets, which were characterized by different spectroscopy techniques such as: Raman scattering, x-ray photoelectron spectroscopy (XPS), UV–Vis and photoluminescence (PL). The Raman analysis showed that the resulting surface is passivated with acetate molecules and also monitored the presence of superficial defects, whose spectroscopic patterns (Raman spectroscopy) indicated that the passivation with acetate molecules reduces the number of defects, such as oxygen vacancies. This result was confirmed by XPS analyses that identified chemisorbed oxygen species onto the oxide surface and an oxygen-deficient component in the sample prepared as reference, without a passivation with EG or PEG. Photoluminescence results showed that the passivation, size and shape of the particles influenced the optical features, mainly at the emission at the green region of spectrum that has been related with surface defects. This green emission is favoured at the ZnO sample prepared without passivation and with large amount of defects. Current–voltage characteristic ( J – V ) of an inverted organic solar cell showed the potential application of these ZnO nanostructures as electron transport material in organic photovoltaic devices.

We describe a direct deposition method for the manufacture of 2D-colloidal crystal films on flexible substrates using a roll-to-roll technique (R2R). Suspensions of silica (SiO2) particles in ethanol with different concentrations and particle sizes (diameters between 150 nm and 520 nm) were prepared and directly deposited onto PET, ITO/PET and stainless steel substrates via wire-bar R2R. We propose an empirical equation that allows one to predict an optimal concentration of the colloidal suspension as a function of the processing parameters necessary to produce a colloidal monolayer. We argue that the development of a R2R coating technique for the fabrication of 2D nanostructures can overcome some technological obstacles that currently hinder the development of printed photonics, nanofabrication and colloidal lithography.

Harnessing solar energy with solar cells based on organic materials (in particular polymeric solar cells) is an attractive alternative to silicon-based solar cells due to the advantages of lower weight, flexibility, lower manufacturing costs, easier integration with other products, low environmental impact during manufacturing and operations and short energy payback times. However, even with the latest efficiencies reported up to 17%, the reproducibility of these efficiencies is not up to par, with a significant variation in the efficiencies reported across the literature. Since these devices are based on ultrathin multilayer organic films, interfaces play a major role in their operation and performance. This review gives a concise account of the major interfacial issues that are responsible for influencing the device performance, with emphasis on their physical mechanisms. After an introduction to the basic principles of polymeric solar cells, it briefly discusses charge generation and recombination occurring at the donor-acceptor bulk heterojunction interface. It then discusses interfacial morphology for the active layer and how it affects the performance and stability of these devices. Next, the formation of injection and extraction barriers and their role in the device performance is discussed. Finally, it addresses the most common approaches to change these barriers for improving the solar cell efficiency, including the use of interface dipoles. These issues are interrelated to each other and give a clear and concise understanding of the problem of the underperformance due to interfacial phenomena occurring within the device. This review not only discusses some of the implemented approaches that have been adopted in order to address these problems, but also highlights interfacial issues that are yet to be fully understood in organic solar cells.

We have performed a study on the effect of the 1,8-diiodooctane (DIO) additive on the performance of an organic bulk-heterojunction solar cell made with PTB7-Th:PC71BM nanostructured blend. The devices were fabricated using either pure chlorobenzene as solvent or mixed with 1,8-diiodooctane. Current-voltage measurements carried in dark, at different temperatures, were analyzed by the Mott-Gurney equation, in which the charge carrier mobility was obtained as fitting parameter. On the sequence, current-voltage curves recorded under 1 Sun illumination, also at different temperatures, were fitted by an analytical equation for the photocurrent, which took into account second-order kinetics for the bimolecular recombination. It is already known that DIO additive selectively dissolves the fullerene and reduces the domain sizes of PC71BM forming a donor-acceptor bicontinuous interpenetrating network, resulting in an increase of the device external quantum efficiency. From the adjustments obtained by the measurements in dark, and that of the photocurrent equation on the photovoltaic responses, we analyzed the effect of temperature on the charge carrier mobility mu and on the recombination reduction factor zeta. It was evident that the effect of DIO on the morphology of the active layer improves the conduction process by hopping, and decreases the recombination coefficient. This improvement of the photocurrent response is most probably due to the fragmentation of the PC71BM aggregates and their better permeation in the polymer matrix of PTB7-Th, which facilitates the dissociation of charge transfer states at PTB7-Th:PC71BM interfaces.

The electrical properties of poly(3-hexylthiophene) (P3HT) are very sensitive to the presence of oxygen, as well as in contact with several metals and oxides that are used as electrodes in organic devices. Such atoms and molecules have deleterious impact on the devices performance, normally causing the diminishing of their efficiency and operation lifetime. Therefore, understanding how those molecules, especially the oxygen, interact with the active layer is mandatory to prevent device degradation. Here we performed CELIV and dark Time-of-Flight measurements in a simplified diode structure ITO/P3HT/Ag before and after exposing the device to ambient air. The results analysis give evidence of a slow intake of oxygen molecules by diffusion, a deliberate filling of the generated oxygen traps by electrons and, consequently, a shift of the P3HT Fermi level toward the HOMO of P3HT. Finally the dynamics of hole extraction during CELIV measurements and their recovery are also discussed.

The low embodied energy within Organic Photovoltaics (OPVs) provides the technology with a characteristic that surpasses all other PV materials. In this work, all-conjugated block copolymers comprising of P3HT and PTB7-Th have been synthesized which enable even lower temperature processibility, thus reducing the embodied energy further. The all-conjugated block copolymers comprise of P3HT and poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b']dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl)] (PTB7-Th). To synthesis these, a narrow-distributed, monobrominated P3HT (M-n=7000, M-w/M-n=1.31) is synthesized by Grignard metathesis polymerisation. This is further reacted with distannyl and dibromo monomers of PTB7-Th by Stille step-growth polycondensation to provide the block copolymers of P3HT-b-PTB7-Th. In these reactions, block ratios are adjusted to 1 to 2 and 1 to 10 based on the numbers of the repeating units of the monomers (i.e. 3-hexylthiophene unit:two monomers of PTB7-Th=1:2 and 1:10). The block copolymer showed hole mobility of 5.9x10(-5) cm(2)/Vs. The highest power conversion efficiency of 3.6%, which was achieved with the photoactive layer processed at 60 degrees C, which is substantially lower than the annealing temperature needed for standard P3HT-based solar cells. Furthermore, the stabilised lifetime of encapsulated devices is enhanced compared to P3HT and PTB7-Th devices, with no drop in efficiency noted for 7 days after initial burn in process.

There is great interest on the study of the semiconductor/dielectric interface of organic field-effect transistors (OFETs), where a conducting channel is formed. Here, we use the interface selectivity, chemical sensitivity, and field-induced enhancement of sum-frequency generation (SFG) vibrational spectroscopy to probe interfacial molecular ordering and degradation processes in poly-3-hexylthiophene (P3HT) OFETs and also the electric field within their dielectric layer (poly(methyl methacrylate), PMMA). P3HT active layers fabricated by the Langmuir-Schaefer method are more orientationally ordered than spin-coated films. Upon electrical degradation of the device in ambient conditions, no noticeable changes were detected in the SFG spectra of the semiconductor/dielectric interface because the sensitivity of our experiment was not enough to detect degraded polymer chains due to loss of SFG electronic resonance enhancement. Perhaps for the same reason, we were also not able to detect any significant changes in the SFG spectra of the P3HT/dielectric interface upon charge accumulation induced by the gate bias. However, we found that upon polarizing the device, PMMA vibrational bands appeared due to field-induced reorientation of its polar groups. Therefore, SFG spectroscopy can be used to probe the electric field within the organic dielectric, including its sign, bringing the possibility of a complete device characterization by nonlinear spectroscopy/microscopy, mapping out the electric field both within the semiconductor and dielectric layers of the OFETs.