Maximum Power Conversion Efficiency Research Articles

Theoretical analysis of the relationship between color and efficiency of the opaque and semitransparent organic photovoltaics

Organic Photovoltaics (OPVs) can be employed on the surfaces of buildings and vehicles owing to its semi-transparent, flexible, and colorful properties. The variety of colors in OPVs improves its aesthetic appearance, besides improving the power conversion efficiency (PCE). This study addresses the relationship between color and efficiency of the opaque or semitransparent devices. By splitting the visual light into wavelength bands, viz. 425–475 nm and 550–600 nm, that are sensitive to the human eyes, accurate color and maximum efficiency has been first obtained in OPVs. The maximum PCE is 33.8% and 33.1% for the opaque and semitransparent devices, respectively. The relative luminosity also affects the PCE of OPVs. While the relative luminosity increases from 0 to 1, the PCE decreases from 33.7% to 13.2% and from 26.4% to 10.2%, for the white opaque and colorless semitransparent OPVs, respectively. Hence the proposed method can be employed to design the OPVs with higher theoretical efficiency and desired accurate color.

High-performance and high-stability LaVO3/Si solar cells through employing thickness-controlled LaVO3 and a titanium oxide passivation layer

LaVO3 is well known as a promising material for use in photovoltaic devices because of its high absorption of visible light. Here, we report on the photovoltaic parameters and photostability of LaVO3/Si/TiOx solar cell devices. In this work, the photovoltaic parameters of the device are controlled via the thickness (t) of the LaVO3 layer; such control is possible because the transmittance, absorbance, and reflectance of this layer are dependent on its thickness. TiOx passivation is also used to reduce the recombination loss at the back surface. Furthermore, TiOx passivation improves the power conversion efficiency (PCE) by blocking recombination at the Si/metal interface. The LaVO3/Si/TiOx cells exhibit a maximum PCE of 6.78% at t = 70 nm. The PCE of the device shows only a 9% decrease after continuous 500 h irradiation at an intensity of 100 mW cm−2 at a temperature of 60 °C and 30–35% relative humidity, suggesting excellent long-term stability.

Defect Passivation for Kesterite CZTSSe Solar Cells via In Situ Al2O3 Incorporation into the Bulk CZTSSe Absorber

A method for in situ Al2O3 incorporation into a Cu2ZnSn(S,Se)4 (CZTSSe) absorber and its effect on solar cell performance is reported. Al2O3‐incorporated CZTSSe films can be prepared by spraying a precursor solution containing Al metal salt dissolved together with Cu, Zn, and Sn metal salts and thiourea. X‐ray photoemission spectroscopy (XPS) and field‐emission transmission electron microscopy (FESEM) reveal the existence of an Al2O3 phase in the CZTSSe film. X‐ray diffraction (XRD) and Raman spectroscopy indicate that Al2O3 incorporation (Al: 0%–2%) does not have a noticeable effect on the crystallization process through postselenization and does not change the lattice parameters of the selenized CZTSSe. However, optimal Al2O3 incorporation is found to reduce the defect level and defect density, as confirmed by various characterization methods, such as 442 nm Raman spectroscopy, photoluminescence, admittance spectroscopy, and temperature‐dependent current density measurements. In addition, Al2O3 incorporation reduces the Urbach energy and back‐contact barrier height. Al2O3 incorporation is found to induce enhancement of Na and O concentrations in the absorber, which facilitates defect passivation effects. Owing to the observed beneficial effects of Al2O3 incorporation, the device performance is significantly enhanced, achieving a maximum power conversion efficiency of 11.76%.

Multi-junction cascade 905 nm vertical cavity surface emitting lasers with high power density

Aiming at three-dimensional (3D) sensing applications such as LiDAR, high power density five-junction cascaded vertical cavity surface emitting lasers (VCSELs) with 905 nm wavelength are designed and fabricated. The maximum power conversion efficiency is 55.2% for an individual VCSEL emitter with 8 μm oxide aperture. And the maximum slope efficiency of the device is 5.4 W/A, which is approximately 5 times that of traditional single-junction VCSEL with the same aperture. Under the condition of narrow pulse (pulse width 5.4 ns, duty cycle 0.019%) injection, the peak output power of 19-element array (20 μm oxidation aperture for each element) reaches 58.3 W, and the corresponding power density is as high as 1.62 kW/mm<sup>2</sup>. The devices with various apertures (8–20 μm) are characterized. The results show that the maximum slope efficiencies of all these devices are greater than 5.4 W/A and the maximum PCE is higher than 54%. These high-performance VCSEL devices can be used as ideal light sources for 3D sensing applications such as LiDAR.

Fabrication of high-efficiency PET polymer-based flexible dye-sensitized solar cells and tapes via heat sink-supported thermal sintering of bilayer TiO2 photoanodes

This work introduces a new type of high temperature material processing technique for the preparation of a bilayer TiO2-coated ITO PET polymer photoanode of flexible dye-sensitized solar cells producing a maximum power conversion efficiency of 6.33%.

Zn-doped CdS/CdSe as efficient strategy to enhance the photovoltaic performance of quantum dot sensitized solar cells

Metal ion doping is a suitable approach for optimizing quantum dots (QDs), which can change the recombination dynamics and charge separation of QDs via creating electronic states within their band gap, and improve their optical and electrical properties. In this work, the transition metal Zn-doped CdS and CdSe QDs are performed by SILAR (successive ionic layer adsorption and reaction) method. And the sensitized solar cells (QDSSCs) based on the Zn-doped CdS and CdSe QDs are assembled. The effect of Zn-doping concentration on the optical properties and charge carrier transport characteristics of photoanodes is investigated. Based on these QDs sensitized TiO2 photoanodes, the assembled QDSSCs with Zn-dopant of a molar concentration of 1.6 mol % exhibited a maximum power conversion efficiency (PCE) of 5.59 %, which is increased by 26.76 % in comparison with that of the QDSSC (4.41%) without Zn-doping. The significantly enhanced PCE of QDSSCs was attributed to improved current density and open-circuit voltage, particularly arising from enhanced light absorbance by narrowing the band gap with the midgap states and upshift of Fermi level promoted by the high electrons concentration due to the ionization of Zn impurities. In addition, the Zn-doping contributes to attenuation of the interfacial charge recombination rate and prolongs the electron lifetime, resulting in more efficient charge collection in QDSSCs.

Synthesis and photophysical properties of N-alkyl dithieno[3,2-b:2',3'-d]pyrrole based donor/acceptor-π-conjugated copolymers for solar-cell application.

Two kinds of donor–acceptor π-conjugated copolymer based on poly{[N-hexyl-dithieno(3,2-b:2′,3′-d)pyrrole-2,6-diyl]alt-[isoindigo]} (PDTP-IID) and poly{[N-hexyl-dithieno(3,2-b:2′,3′-d)pyrrole-2,6-diyl]alt-[thiazol-2,5-diyl]} (PDTP-Thz) were investigated. These copolymers were synthesized via a Stille coupling reaction. The results showed the structure–property relationships of different donor–acceptor (D–A) combinations. The polymer structures and photophysical properties were characterized by 1H NMR, TGA, DSC, UV-vis absorption spectroscopy, AFM, CV, and XRD measurement. Through UV-vis absorption and cyclic voltammetry (CV) measurements, it showed that the copolymers exhibit not only a low bandgap of 1.29 eV and 1.51 eV but also a deep highest occupied molecular orbital (HOMO) of −5.49 and −5.11 eV. Moreover, photovoltaic properties in combination with the fullerene derivatives were investigated. The device based on the copolymers with PC71BM exhibited higher maximum power conversion efficiency and higher maximum short-circuit current density of 0.23% with 1.64 mA cm−2 of PDTP-IID:PC71BM and 0.13% with 1.11 mA cm−2 of PDTP-Thz:PC71BM than those of the copolymers with PC61BM. Measurements performed for N-hexyl-dithieno(3,2-b:2′,3′-d)pyrrole-based copolymers proved the potential of these polymers to be applied in optoelectronic applications.

Optimization of Hole and Electron Transport Layer for Highly Efficient Lead-Free Cs2TiBr6-Based Perovskite Solar Cell

The methylammonium lead halide solar cell has attracted a great deal of attention due to its lightweight, low cost, and simple fabrication and processing. Despite these advantages, these cells are still far from commercialization because of their lead-based toxicity. Among lead-free perovskites, cesium-titanium (IV) bromide (Cs2TiBr6) is considered one of the best alternatives, but it faces a lack of higher PCE (power conversion efficiency) due to the unavailability of the matched hole and electron transport layers. Therefore, in this study, the ideal hole and electron transport layer parameters for the Cs2TiBr6-based solar cell were determined and discussed based on a simulation through SCAPS-1D software. It was observed that the maximum PCE of 20.4% could be achieved by using the proper hole and electron transport layers with optimized parameters such as energy bandgap, electron affinity, doping density, and thickness. Unfortunately, no hole and electron transport material with the required electronic structure was found. Then, polymer NPB and CeOx were selected as hole and electron transport layers, respectively, based on their closed electronic structure compared to the simulation results, and, hence, the maximum PCE was found as ~17.94% for the proposed CeOx/Cs2TiBr6/NPB solar cell.

Nanocrystalline Sb-doped-BaSnO3 perovskite electron transport layer for dye-sensitized solar cells

Undoped and Sb-doped BaSn(1-x)SbxO3 (x = 0, 0.01 and 0.03) perovskite nanoparticles are synthesized using a facile peroxide-precipitate method and annealed at 900 °C for 2 h in air. Rietveld refinement of X-ray diffraction data indicates single-phase cubic structure which also corroborates with transmission electron microscopy data. Reduction in reflectance intensity and optical bandgap is observed with Sb-doping. Dye-sensitized solar cell fabricated using nanocrystalline BaSn(1-x)SbxO3 at x = 0.01 as electron transport layer shows maximum power conversion efficiency of 4.06% and short-circuit current density of 9.97 mAcm−2, substantiating the electrochemical impedance data.

Mechanochemistry Advances High-Performance Perovskite Solar Cells.

A prerequisite for commercializing perovskite photovoltaics is to develop a swift and eco-friendly synthesis route, which guarantees the mass production of halide perovskites in the industry. Herein, a green-solvent-assisted mechanochemical strategy is developed for fast synthesizing a stoichiometric δ-phase formamidinium lead iodide (δ-FAPbI3 ) powder, which serves as a high-purity precursor for perovskite film deposition with low defects. The presynthesized δ-FAPbI3 precursor possesses high concentration of micrometer-sized colloids, which are in favor of preferable crystallization by spontaneous nucleation. The resultant perovskite films own preferred crystal orientations of cubic (100) plane, which is beneficial for superior carrier transport compared to that of the films with isotropic crystal orientations using "mixture of PbI2 and FAI" as precursors. As a result, high-performance perovskite solar cells with a maximum power conversion efficiency of 24.2% are obtained. Moreover, the δ-FAPbI3 powder shows superior storage stability for more than 10 months in ambient environment (40± 10% relative humidity), being conducive to a facile and practical storage for further commercialization.

P-Tetrafluorophenylene Divinylene-Bridged Nonfullerene Acceptors as Binary Components or Additives for High-Efficiency Organic Solar Cells

In this study, we designed, synthesized, and characterized an A-D-A'-D-A-type indacenodithienothiophene (IDTT)-based molecular acceptor that exhibited a broader absorption range and higher lowest unoccupied molecular orbital energy level with a nearly comparable band gap compared to a well-known electron acceptor IT-M. The designed electron-deficient molecular acceptor FB-2IDTT-4Cl with a fluorinated benzene tether (FB), that is, p-tetrafluorophenylene divinylene, demonstrated long-wavelength absorption and high hole and electron charge mobility in the thin films blended with the electron donor PBDB-T for an inverted organic photovoltaic (OPV) binary device, resulting in a maximum power conversion efficiency (PCE) of 11.4%. Such a performance is comparably as high as that of the device with PBDB-T:IT-M, and particularly, it was 18.8% higher than that of the devices with ITIC-4Cl as the acceptor (PCE 9.1% ± 0.5%) and 24.9% higher than that of the devices with the thiophene-flanked benzothiadiazole-bridged acceptor CNDTBT-IDTT-FINCN (PCE 9.01% ± 0.13%). Furthermore, varying the illumination intensity from 200 to 2000 lux increased the Jsc and Voc values as well as the FF values, thus leading to increased PCE levels. In addition, the best PCE of the PM6:Y6 device with 1% FB-2IDTT-4Cl as additives was 16.9%. Our stability test showed that the PM6:Y6 standard device efficiency downgraded very soon either at room temperature or under thermal-annealing conditions. However, with the addition of 1% FB-2IDTT-4Cl as additives, the device efficiency still can be maintained at 90-95% in 500 h at room temperature and 95% at 20 h and 85-95% in 45 h at an annealing temperature of 80 °C. These findings demonstrate FB-2IDTT-4Cl to be a promising candidate as an electron acceptor with a fluorinated π-bridging fused-ring design for OPV applications.

Hot-Casting and Anti-solvent Free Fabrication of Efficient and Stable Two-Dimensional Ruddlesden-Popper Perovskite Solar Cells.

Owing to the durable environmental stability and tunable photophysical properties of the two-dimensional Ruddlesden-Popper (2D RP) perovskite, it has a great potential in stable perovskite solar cells (pero-SCs). However, almost efficient 2D RP pero-SCs are prepared by the hot-casting or anti-solvent assisted spin-coating method, which greatly limits their applications. Herein, a multifunctional strategy through introducing a novel organic salt, benzimidazolium iodide (BnI), as a spacer and KI as an additive is reported to successfully fabricate a high-quality Bn-based 2D RP perovskite film in the hot-casting and anti-solvent free spin-coating method. The entire conjugated backbone of benzimidazolium is expected to enhance charge carrier transport within the 2D RP perovskite film. And KI can lead to a preferred orientation and less defects in the 2D RP perovskite film. Then, a maximum power conversion efficiency (PCE) of 15.12% is obtained, which is the highest performance for 2D RP perovskite devices without the hot-casting or anti-solvent method. The unsealed device maintains 92.1% of its original performance when kept in air (40-45% relative humidity) for 720 h and 87.9% of the initial performance after 528 h of heating at 85 °C.

Graded Morphologies and the Performance of PffBT4T-2OD:PC71BM Devices Using Additive Choice.

The impact of several solvent processing additives (1-chloronaphthalene, methylnaphthalene, hexadecane, 1-phenyloctane, and p-anisaldehyde), 3% v/v in o-dichlorobenzene, on the performance and morphology of poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3‴-di(2-octyldodecyl)-2,2′,5′,22033,5″,2‴-quaterthiophen-5,5‴-diyl)] (PffBT4T-2OD):[6,6]-phenyl-C71-butyric acid methyl ester (PC71BM)-based polymer solar cells was investigated. Some additives were shown to enhance the power conversion efficiency (PCE) by ~6%, while others decreased the PCE by ~17–25% and a subset of the additives tested completely eliminated any power conversion efficiency and the operation as a photovoltaic device. Grazing-Incidence Wide Angle X-ray Scattering (GIWAXS) revealed a clear stepwise variation in the crystallinity of the systems when changing the additive between the two extreme situations of maximum PCE (1-chloronaphthalene) and null PCE (hexadecane). Small-Angle Neutron Scattering (SANS) revealed that the morphology of devices with PCE ~0% was composed of large domains with correlation lengths of ~30 nm, i.e., much larger than the typical exciton diffusion length (~12 nm) in organic semiconductors. The graded variations in crystallinity and in nano-domain size observed between the two extreme situations (1-chloronaphthalene and hexadecane) were responsible for the observed graded variations in device performance.

Copper (I) selenocyanate (CuSeCN): Eco-friendly solution-processable deposition of hole transport layer for organic solar cells

Recently, a lot of research on solution-processable deposition of copper (I) thiocyanate (CuSCN) as an efficient hole transport layer (HTL) for solar cells has been reported. Herein, we report the higher chalcogen analogue copper (I) selenocyanate (CuSeCN), as efficient HTL for organic solar cells. Eco-friendly and inexpensive DMSO and DMF solvents were used for solution-processable deposition of CuSeCN thin films. The optical, electrical, and morphological properties of the HTL were studied using UV–vis-NIR spectroscopy, cyclic voltammetry, and scanning electron microscopy. Density functional theory calculations were performed to understand the HOMO level and band gap of the HTL. Two different concentrations of CuSeCN solution (DMSO and DMF) were used for HTL deposition for fabrication of photovoltaic devices. Photovoltaic devices were fabricated with a simple device geometry ITO/CuSeCN/PCDTBT:PC71BM/Al and maximum power conversion efficiencies were achieved up to 3.92% and 4.03% using DMSO and DMF as deposition solvents, respectively under ambient conditions, which are comparable to devices made by PEDOT:PSS and MoOx as HTLs under identical conditions.

Insight into the role of selenization time for highly efficient Mn doped Cu2ZnSn(S,Se)4 thin film based solar cells

In this study, manganese (Mn) doped Cu2ZnSn(S,Se)4 (CMZTSSe) absorption layer films were prepared using a sol–gel method followed by a selenization treatment in a selenium environment. In this paper, we discuss the impact of annealing time on the structure, morphology, and properties of CMZTSSe absorption layer films. The crystal quality of the CMZTSSe films increased, and the major Se occupied the position in CMZTSSe with the increase of the annealing time. When the annealing time was 15 min, a smooth and dense film was obtained. The band gap of CMZTSSe was adjusted between 1.19 and 1.09 eV by adjusting the post-annealing time. The influence mechanisms of the annealing time on the performance of a solar cell were investigated by systematically learning the variation in the shunt resistance (RSh) and series resistance (RS) with the microstructure of the CMZTSSe films selenized at different times. The results showed that the power conversion efficiency (PCE) initially increased and then decreased when the annealing time was increased from 10 to 20 min. The VOC, JSC, and FF have similar change regularity with that of the PCE. At an annealing time of 15 min, the CMZTSSe film had the best crystal quality, RS was at minimum, and RSh was at maximum. The CMZTSSe device achieved a maximum PCE of 4.27%, VOC was 382 mV, JSC was 26.35 mA/cm 2, and FF was 42.34%.

Efficiency and Stability Enhancement of Perovskite Solar Cells Utilizing a Thiol Ligand and MoS2 (100) Nanosheet Surface Modification

Surface modification of perovskite films using a combination of 1-dodecanethiol (DT) and MoS2 nanosheets is investigated for perovskite solar cells. This surface modification is studied for two different types of perovskites, one with triple cations (CsFAMA) and one with double cations (FAMA), resulting in solar cell devices with power conversion efficiency (PCE) values of 18–19 and >20%, respectively. In both cases, stability enhancement is observed with DT and MoS2 surface modification using three different stability tracking protocols. The results reveal that by including DT and MoS2, the device retains 92% of its highest efficiency after 2200 h in dark (in air), while the standard device retained only 72%. Moreover, after light cycling, the device with DT and MoS2 retained 80%, and the standard device retained 55% of its maximum PCE. Moreover, these surface modifications gave rise to 58% decrease in the number of short-circuited devices and more reproducible results. Different characterizations revealed that the stability and efficiency enhancement is mainly due to reduced interface trap densities, improved charge transfer, and longer charge carrier lifetime. Moreover, the DT and MoS2 modifications induce hydrophobicity with an average contact angle over 80°.

Research on the Performance of Nuclear Battery with SiC-Schottky and GaN-PIN Structure

The fabrication and experimental research of a GaN-Positive-Intrinsic-Negative (GaN-PIN) betavoltaic nuclear battery driven by an 63Ni radioisotope source and an SiC-Schottky betavoltaic nuclear battery driven by an 147Pm radioisotope source are introduced. The self-absorption effects of radioisotope sources (63Ni, 147Pm) are explored and analyzed by Monte Carlo simulation. The SiC-Schottky and GaN-PIN betavoltaic cells were fabricated, where the GaN-PIN devices include different areas, absorption layer thicknesses, and electrode structures. And the measured I–V results show that the power density of the GaN-PIN nuclear battery can exceed 4.3 nW/cm2, the open-circuit voltage can reach 1.25 V, and the energy conversion efficiency can reach 2.3%. And for the SiC-Schottky betavoltaic battery, the maximum output power and energy conversion efficiency are 0.67 pW/cm2 and 0.024%, respectively.

Similarity principle based multi-physical parameter unification and comparison in salinity-gradient osmotic energy conversion

Nanofluidic osmotic energy conversion has the potential of directly converting renewable salinity-gradient energy into electricity. Existing research mainly focuses on the ion selectivity and robustness of nanoporous membranes. However, the multi-physical governing parameters of salinity-gradient osmotic energy conversion have never been unified and compared. In the current study, a similarity principle is constructed for ion selective transport in nanofluidic channel through dimensionless analysis, which lays a theoretical foundation for experimental design and data analysis to develop engineering correlations in osmotic energy conversion under a salinity-gradient. The derived dimensionless governing parameters are grouped into four categories with different physical meanings including ion driving source, ion selectivity, ion transport characteristics, and nanoporous membrane configuration. Particularly, a key dimensionless governing parameter named “IonS” is developed for ion selectivity of nanofluidic channel, indicating that the ion selectivity has a positive linear correlation with the nanochannel surface charge density and a negative linear correlation with ion concentration and nanofluidic channel radius. Considering the similarity phenomena in salinity-gradient osmotic energy conversion, future experimental burden is dramatically alleviated. In addition, a sensitivity analysis using Taguchi method is carried out to evaluate the dominance order of multi-physical parameters in salinity-gradient osmotic energy conversion. The ion concentration and nanofluidic channel radius are found to be dominant for maximum output power and energy conversion efficiency because of their significant influences on the thickness of electric double layer and its overlapping degree. The current dimensionless analysis based similarity principle and sensitivity analysis of multi-physical parameters offer an intrinsic insight for ion selective transport in nanofluidic channels, contributing to the development of salinity-gradient osmotic energy conversion for practical applications.

Growth and photovoltaic device using Cu3VS4 films prepared via co-sputtering from Cu–V and V targets

CVS (Cu3VS4) materials have the potential to become a new generation of thin film solar cell absorber materials, due to the availability of the constituent materials and a nearly ideal energy gap (1.3–1.5eV). In this study, we investigated the effects of co-sputtering using targets of Cu–V and V and various sulfurization temperatures to produce thin films of various Cu/V ratios. In experiments, CVS films with a high Cu/V ratio presented large surface grains of Cu2-XS with the appearance of secondary phases (CuS, Cu1.8S, Cu2S, and Cu0.7V2.3S4) during H2S sulfurization process. A low Cu/V ratio with high sulfurization temperature produced nearly single-phase CVS. The optimal CVS absorber layer was prepared using a Cu/V ratio of 2.76 with sulfurization for 20 min at a temperature of 550 °C. A prototype CVS thin film solar cell achieved a maximum power conversion efficiency of 3.11%.

Surface dipole assisted charge carrier extraction in inverted architecture perovskite solar cells

Engineering the energetics of perovskite solar cells through the introduction of surface dipoles that assist with charge carrier extraction is a promising route to enhance the device performance without altering other device layers or fabrication parameters. In this work, we introduce four different derivatives of dicationic phosphonium-bridged ladder stilbenes (PYMC) in inverted perovskite solar cells with the device structure of ITO/Meo-2pacz/perovskite/PYMC/phenyl-C61-butyric acid methyl ester (PCBM)/bathocuproine/Ag. We show that the derivatives introduce a dipole at the perovskite/PCBM interface, which for derivatives with suitable energy levels can enhance the charge carrier extraction, leading to a quenched photoluminescence of perovskite thin films and an improved photovoltaic performance. As a result, both a higher average and maximum power conversion efficiency could be achieved and an overall better device reproducibility. This work highlights the significant potential of energetics engineering between perovskites and transport layers in perovskite solar cells for highly efficient photovoltaic devices.