Enhancement Of Open-circuit Voltage Research Articles

Role of cation-mediated recombination in perovskite solar cells

The origin of the hysteresis in the current–voltage (J–V) characteristics in perovskite solar cells (PSCs) is one of the most debated topics of recent years. Hysteretic effects are connected with the slow redistribution of ionic defects during the voltage sweep. Existing literature focuses on the potential screening due to accumulated ions, solely, while neglecting the possibility of charge trapping and subsequent recombination via ions. We investigate the role of cation-mediated recombination of ions using time-dependent drift–diffusion simulations in MAPbI3 PSCs. Slow-moving cations are considered as traps for the electrons. Trapped electrons can subsequently recombine non-radiatively with holes. We analyze the role of the cation-mediated trapping and its parameters (capture coefficient, cation energy, ion mobility) as well as the scan rate on the device performance. For shallow cation energies, a decrease in open-circuit voltage and slight enhancement in hysteresis is observed. Deep cation energies lead to a substantial deterioration of device performance and large hysteresis enhancement. The presented study emphasizes the importance of considering the interaction of ions with charge carriers beyond the simple electrostatic models to improve our understanding of PSCs.

Tailoring multifunctional passivation molecules with halogen functional groups for efficient and stable perovskite photovoltaics

The ionic nature of hybrid perovskites indicates the existence of inevitable and multi-type defects. Design of effective passivation molecules becomes a vital means to suppress charge recombination and reduce the voltage loss in perovskite solar cells. However, most of the reported passivation molecules show single effect and the passivation mechanism of molecules with multiple functional groups is unclear. Herein, on the premise of making sure the combined passivation effect of amine, carbonyl group and benzene ring, we tailored multifunctional passivation molecules (4-fluorobenzamide and 4-chlorobenzamide) by introducing halogen functional group. After employing high-electronegativity halogen groups, the hydrogen bond with organic cations and ionic bond with Pb2+ were formed, which is the key to prevent defect regeneration and ion migration. The perovskites with halogenated passivation molecules displayed reduced trap densities and increased carrier lifetimes. Finally, multifunctional passivation molecules can not only effectively heal defects but also improve the stability of perovskite materials. The optimal devices with 4-fluorobenzamide achieved a 5.6% enhancement of open-circuit voltage (Voc) and the power conversion efficiency yielded to 21.35%. Our findings confirm the enhanced passivation based on the multiple functional groups combination and provide a guideline for new multifunctional passivation molecules in perovskite photovoltaics.

Relieving unwanted strain

Solar Cells Although the α-phase of formamidinium lead iodide (FAPbI3) has a suitable bandgap for use in solar cells, it must be stabilized with additional cations. These compositions can adversely affect the bandgap and produce lattice strain that creates trap sites for charge carriers. Kim et al. found that substituting small, equimolar amounts of cesium and methylenediammonium cations for formamidinium reduced the lattice strain and trap densities. The enhancement in open-circuit voltage led to a certified power conversion efficiency of 24.4%, and encapsulated devices retained 90% of their initial efficiency after 400 hours of maximal power point operating conditions. Science , this issue p. [108][1] [1]: /lookup/doi/10.1126/science.abc4417

First theoretical framework of Z-shaped acceptor materials with fused-chrysene core for high performance organic solar cells.

Chrysene core containing fused ring acceptor materials have remarkable efficiency for high performance organic solar cells. Therefore, present study has been carried out with the aim to design chrysene based novel Z-shaped electron acceptor molecules (Z1-Z6) from famous Z-shaped photovoltaic material FCIC (R) for organic photovoltaic applications. End-capped engineering at two electron-accepting end groups 1,1-dicyanomethylene-3-indanone of FCIC is made with highly efficient end-capped acceptor moieties and impact of end-capped modifications on structure-property relationship, photovoltaic and electronic properties of newly designed molecules (Z1-Z6) has been studied in detail through DFT and TDDFT calculations. The efficiencies of the designed molecules are evaluated through energy gaps, exciton binding energy along with transition density matrix (TDM) analysis, reorganizational energy of electron and hole, absorption maxima and open circuit voltage of investigated molecules. The designed molecules exhibit red-shift and intense absorption in near-infrared region (683-749nm) of UV-Vis-NIR absorption spectrum with narrowing of HOMO-LUMO energy gap from 2.31eV in R to 1.95 in eV in Z5. Moreover, reduction in reorganization energy of electron from 0.0071 (R) to 0.0049 (Z5), and enhancement in open circuit voltage from 1.08V in R to 1.20V in Z5 are also observed. Twisted Z-shape of designed molecules prevents self-aggregation that facilitates miscibility of donor and acceptor. Low values of binding energy, excitation energy, and reorganizational energy (electron and hole) suggest that novel designed molecules offer high charge mobilities as compared to FCIC. Our findings indicate that these novel designed molecules can display better photovoltaic parameters and are suitable candidates if used in organic solar cells.

Enhanced output performance of flexible piezoelectric energy harvester by using auxetic graphene films as electrodes

We demonstrate an effective approach to enhance the output performance of a flexible piezoelectric energy harvester by using flexible electrodes with negative Poisson's ratio (NPR). The relationship between open-circuit voltage and Poisson's ratio of electrodes is established theoretically by deriving the analytical expression. It reveals a continuous increasing trend in open-circuit voltage with the decrease in Poisson's ratio of the electrodes. Further, graphene-assembled macro-film (GAMF), an NPR material with excellent flexibility and high conductivity, is used as the electrodes to fabricate flexible piezoelectric energy harvesters. Compared with the energy harvesters using silver electrode, the harvesters made by GAMF electrodes, with an NPR of −0.39, achieve nearly 1.7-times enhancement in open-circuit voltage and 1.6-times in short-circuit current for output performance. The experimental results are highly consistent with the simulation results, indicating that the GAMF has great prospects in developing flexible piezoelectric energy harvesters with enhanced electrical output performance.

Enhanced stability and photovoltaic performance of planar perovskite solar cells through anilinium thiobenzoate interfacial engineering

Organic-inorganic halide perovskite absorbers remain top contenders for current photovoltaic technologies owing to their ability to attain high efficiency at relatively low cost. However, commercialization of perovskite solar cells remains difficult due to their poor long-term stability. Such instability is commonly attributed to the ease in defect formation within the polycrystalline absorber film as well as at the surfaces between the layers, acting as recombination centers, reducing the overall performance of the device. Introduction of suitable interfacial layers has proven effective in defect passivation, allowing enhanced device stability and improving photovoltaic performance. In this study, a novel anilinium thiobenzoate (ATB) interlayer is deposited between the perovskite/hole transport layer (HTL) interface. Since ATB contains functional groups such as sulfur and ammonium, favourable coordination with under-coordinated lead ions on the perovskite film allows significant reduction in recombination losses and enhancement of open-circuit voltage from 1.05 to 1.11 V. Apart from the paramount efficiency of 19.33%, the 10 mg/mL ATB passivated device also shows exceptional long-term stability whereby 92% of initial efficiency is retained despite storage in ambient conditions for 150 days. Hence, results from this study highlights the importance of device passivation in attaining superior device performance and long-term stability.

Effects of Mg% on open circuit voltage and short circuit current density of Zn1-xMgxO/Cu2O heterojunction thin film solar cells, processed using electrochemical deposition and spin coating

Zn1-xMgxO/Cu2O/Ag solar cells were fabricated upon fluorine doped tin oxide coated soda lime glass substrate with varying percentage of Mg mol% doping in zinc oxide (ZnO) layer. Short circuit current density & open circuit voltages of the fabricated cells were investigated. Optimum doping with Mg improved the transparency of ZnO layer which helped in increasing the short circuit current density of solar cells. An enhancement of open circuit voltage was observed with increase in x, which was investigated using X-ray photoelectron spectroscopy and the results revealed that with increase in x, there was a decrease in conduction band offset between Zn1-xMgxO and cuprous oxide layers. From UV-Visible transmittance spectra, it was observed that with Mg doping in ZnO nanostructure, optical losses were reduced which resulted in increase in Short circuit current density. The objective of this study was to investigate and develop a technology for fabrication of solar cells that is both cost effective and easy to produce.

Aminonaphthoquinones as photosensitizers for mesoporous ZnO based dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) were fabricated on mesoporous ZnO using different novel 2R-(n-alkylamino)-1,4-naphthoquinone photosensitizers, viz; HA3; (2-propylamine-1,4-naphthoquinone), HA4; (2-butylamino-1,4-naphthoquinone), BrA3; (2-bromo-3-propylamino-1,4-naphthoquinone), BrA4; (2-bromo-3-butylamino-1,4-naphthoquinone). The crystallinity, morphology, optical, and electrochemical properties of the photosensitizers loaded ZnO were investigated by FE-SEM, UV–visible spectroscopy and J-V characteristics. Scanning electron micrograph (FE-SEM) indicates the surface morphologies of ZnO structures. A broad band of photosensitizers in UV region assigned to π → π∗ transition while a visible region band assigned to n → π∗ charge transfer transition. Powder XRD pattern of mesoporous ZnO on fluorine-doped tin oxide (FTO) confirmed the presence of single-phase hexagonal wurtzite structure, without the impurity phase. DSSCs based on mesoporous ZnO electrodes were fabricated using these photosensitizers with an impressive power conversion efficiency of 0.12, 0.09, 0.13, and 0.20% obtained for HA3, HA4, BrA3 and BrA4 photosensitizers. The current-voltage measurements of DSSCs based on mesoporous ZnO showed an enhancement of open-circuit voltage (Voc) from 0.29 to 0.33V. It confirms its active role photosensitizers for the energy barrier leading to a decrease in recombination losses. The unique mesoporous ZnO acts as the template for photogenerated charges and forms a barrier to reduce the recombination rate of the photoinjected electron-hole pairs at the electrode−electrolyte interface.

Double‐Layer electron transporting layer for efficient lead sulfide quantum dots solar cells

Herein, for the first time, the role of double-layer electron transporting layer (ETL), i.e. ZnO/SnO 2 on the efficiency of lead sulfide quantum dots solar cells is demonstrated. Using this approach, a device with power conversion efficiency of 10.6% is achieved mainly due to the enhancement of open circuit voltage ( V OC ). The authors reduce the loss-in-potential by 80 mV using ZnO/SnO 2 double-layer ETL.

In brief

PAGE 771 Researchers from Vietnam present a study on how multiple users affect the performance of NOMA networks over α−κ−μ fading channels. The exact expressions in terms of ergodic capacities and outage probabilities are derived, along with a comparison with OMA under such shadowed fading. PAGE 787 A study into how double-layer electron transporting layers affects the efficiency of lead sulfide quantum dots solar cells is presented. A device with power conversion efficiency of 10.6% is achieved due to the enhancement in open circuit voltage. The loss-in-potential is reduced by 80 mV by use of the double-layer ZnO/SnO2 electron transporting layer. Ergodic Rate (BCPU) versus the average transmit SNR. PAGE 753 A correction algorithm for time-interleaved analog-to-digital converters (TIADAC) in order to solve the problem of calibration failure caused by frequency timing mismatch exceeding sub-Nyquist frequency is presented. The proposed technique consumes less hardware and works well without employing a band-pass filter or reference channel. Simulations show the calibration is effective throughout the entire Nyquist band of TIADC. Schematic of PbS QDs solar cell fabricated on ZnO/SnO2 ETL. PAGE 780 A novel out-of-plane integration of multilayer strip resonators is proposed. The structure retains the merit of traditional in-plane integrated devices whilst achieving the same amount of coupling with smaller horizontal space between resonators. Overall a 52.4% reduction in size is achieved whilst comparable performance is maintained. Block diagram of improved calibration direction correction algorithm. PAGE 782 German and British researchers present an implementation of two amplifiers in a commercial, flexible a-IGZO TFT technology. The amplifiers significantly outperform previously flexible a-IGZO TFT amplifiers in terms of bandwidth, gain-bandwidth product, unity-gain frequency, power consumption and area. The input sensitivity of a-IGZO TFT wireless systems can be increased considerably by using the amplifier circuit. Measurement of re-designed band-pass filter, samples in inset photograph. Schematic of CS amplifier.

Improved interfacial property by small molecule ethanediamine for high performance inverted planar perovskite solar cells

Abstract We report a simple and effective method to realize desirable interfacial property for inverted planar perovskite solar cells (PSCs) by using small molecule ethanediamine for the construction of a novel polyelectrolyte hole transport material (P3CT-ED HTM). It is found that P3CT-ED can not only improve the hole transport property of P3CT-K but also improve the crystallinity of adjacent perovskite film. In addition, the introduction of ethanediamine into P3CT realigns the conduction and valence bands upwards, passivates surface defects and reduces nonradiative recombination. As a consequence, compared to P3CT-K hole transport layer (HTL) based devices, the average power conversion efficiency (PCE) is boosted from 17.2% to 19.6% for the counterparts with P3CT-ED, with simultaneous enhancement in open circuit voltage and fill factor. The resultant device displays a champion PCE of 20.5% with negligible hysteresis.

Simulating the effect of adding BSF layers on Cu2BaSnSSe3 thin film solar cells

In this paper, the device characteristics of Cu2BaSnSSe3 (CBT(S,Se3)) solar cells have been simulated using SCAPS-1D. The simulated results have been validated by comparison with the experimental data reported in the literature. For improving the cell performance and boosting the efficiency, adding different Back Surface Field (BSF) layers is suggested on the absorber layer. Inserting a BSF layer with optimum parameters causes enhancement of open-circuit voltage (VOC), in particular, causes better efficiency on the cell's performance. For this purpose, we optimize the MoSe2 layer, which is formed at the interface between CBT(S,Se3) absorber layer and Mo back contact. Investigation of MoSe2 helps us to represent optimum ranges for bandgap (Eg), electron affinity (χ), charge carrier density, thickness, the mobility of electron and hole (μe and μh) and the effective density of states of conduction band and valence band (NC and NV) of a material to choose as a BSF layer which can be inserted in CBT(S,Se3) solar cells and other types of cells like CZTSSe, perovskite and CIGS. Based on the optimum parameters for an appropriate BSF layer, Cu2BaSnSSe3 solar cell has been simulated by inserting SnS as a BSF layer, and the results indicated improvement in the cell's parameters. We recorded PCE = 7.31%, VOC = 0.867 V, JSC = 16.986 mA/cm2, and FF = 49.63%.

High-Efficiency Perovskite Quantum Dot Hybrid Nonfullerene Organic Solar Cells with Near-Zero Driving Force.

To take advantages of the intense absorption and fluorescence, high charge mobility, and high dielectric constant of CsPbI3 perovskite quantum dots (PQDs), PQD hybrid nonfullerene organic solar cells (OSCs) are fabricated. Addition of PQDs leads to simultaneous enhancement of open-circuit voltage (VOC ), short-circuit current density (JSC ), and fill factor (FF); power conversion efficiencies are boosted from 11.6% to 13.2% for PTB7-Th:FOIC blend and from 15.4% to 16.6% for PM6:Y6 blend. Incorporation of PQDs dramatically increases the energy of the charge transfer state, resulting in near-zero driving force and improved VOC . Interestingly, at near-zero driving force, the PQD hybrid OSCs show more efficient charge generation than the control device without PQDs, contributing to enhanced JSC , due to the formation of cascade band structure and increased molecular ordering. The strong fluorescence of the PQDs enhances the external quantum efficiency of the electroluminescence of the active layer, which can reduce nonradiative recombination voltage loss. The high dielectric constant of the PQDs screens the Coulombic interactions and reduces charge recombination, which is beneficial for increased FF. This work may open up wide applicability of perovskite quantum dots and an avenue toward high-performance nonfullerene solar cells.

Influence of the Carrier Selective Front Contact Layer and Defect State of a-Si:H/c-Si Interface on the Rear Emitter Silicon Heterojunction Solar Cells

In this research, simulations were performed to investigate the effects of carrier selective front contact (CSFC) layer and defect state of hydrogenated amorphous silicon passivation layer/n-type crystalline silicon interface in silicon heterojunction (SHJ) solar cells employing the Automat for Simulation of hetero-structure (AFORS-HET) simulation program. The results demonstrated the effects of band offset determined by band bending at the interface of the CSFC layer/passivation layer. In addition, the nc-SiOx: H CSFC layer not only reduces parasitic absorption loss but also has a tunneling effect and field effect passivation. Furthermore, it increased the selectivity of contact. In the experimental cell, nc-SiOx:H was used as the CSFC layer, where efficiency of the SHJ solar cell was 22.77%. Our investigation shows that if a SiOx layer passivation layer is used, the device can achieve efficiency up to 25.26%. This improvement in the cell is mainly due to the enhancement in open circuit voltage (Voc) because of lower interface defect density resulting from the SiOx passivation layer.

3D Structural Optimization of Zinc Phthalocyanine-Based Sensitizers for Enhancement of Open-Circuit Voltage of Dye-Sensitized Solar Cells

We designed and synthesized two zinc phthalocyanine sensitizers (PcS27 and PcS28), substituted with branched or cyclic alkoxy chains, to investigate the structural effect of peripheral alkyl chains on the performance of dye-sensitized TiO2 solar cells. The bulky cyclic alkyl chains of PcS28 decreased the adsorption density of PcS28 on the TiO2 electrode, while the terminal branches of alkoxy chains of PcS27 did not influence the adsorption density in comparison to the previously published PcS20 with linear alkoxy chains. Under one sun conditions, PcS27 cells exhibited higher open-circuit voltage but a slightly lower energy conversion efficiency, 6.0% less than PcS20. These results suggest that the small alternation of alkoxy chains resulted in decreasing electron pushing ability of peripheral phenoxy units, giving lower short-circuit current.

Cu2O-HTM/SiO2-ETM assisted for synthesis engineering improving efficiency and stability with heterojunction planar perovskite thin-film solar cells

Perovskite solar cells (PSCs) have been made eligible for proficient power conversion efficiency (PCE) by optimizing the perovskite film’s morphology, formation, interfaces, and charge collection for increased effectiveness. This paper applied a new method for Cu2O/methylammonium lead iodide (MAPbI3)/SiO2 structure with heterojunction PSCs. This paper developed a novel synthesis engineering method for thin Cu2O hole-transporting material layer (HTML) and ultrathin SiO2 electron-transporting material layer (ETML). Cu2O HTML and SiO2 ETML could improve the PCE and carrier charge for recombination and recollection. The architecture includes a reduced film thickness by hetero-contact synthesis engineering, which resulted in an impactful enhancement of open-circuit voltage (Voc). The stable Voc effect was induced by constructing the interfilm of Cu2O and SiO2 between the main CH3NH3PbI3 layers, which transported electrons/electron holes, resulting in an excellent PCE of 18.4%. The fabrication showed that inorganic materials can be applied for the potential interfacial engineering of perovskite-based solar cells.

Device simulation of 17.3% efficient lead-free all-perovskite tandem solar cell

Present research paper brings forth the results of simulation-based studies carried out on all-perovskite tandem (both top and bottom subcells made up of perovskites) multijunction devices. The all-perovskite tandem structure presented in this work employs a wide bandgap perovskite, i.e., Cs2AgBi0.75Sb0.25Br6 (1.8 eV) and a narrow bandgap perovskite, i.e., FACsPb0.5Sn0.5I3 (1.2 eV) as top and bottom cell respectively. An additional merit of the reported work is projection of lead (Pb)-free perovskite, Cs2AgBi0.75Sb0.25Br6 and low Pb content-based perovskite, FACsPb0.5Sn0.5I3 based tandem solar cell. The viability of proposed tandem design is performed in two steps firstly, 1.8 eV perovskite-based top cell is simulated and calibrated to fit the state-of-the-art conversion efficiency of 10.1%, and then, 1.2 eV perovskite-based bottom cell is simulated to have a calibrated efficiency of 14.2%. After calibrating the standalone (top and bottom) subcells, both the devices are evaluated for tandem configuration. The current matching conditions between the top and bottom cell is obtained at different thicknesses of the absorber layer in both top and bottom subcell. The optimized thickness for perovskite, 380 nm for top cell and 400 nm for bottom cell are obtained for tandem configuration. Top and bottom cells (fed with the filtered spectrum) reflect the conversion efficiency of 10.01% and 7.36%, respectively. Overall, tandem design showed a conversion efficiency of 17.3% owing to an enhancement in open-circuit voltage (VOC), which is 1.83 V.

Impact of RbF-PDT on Cu(In,Ga)Se2 solar cells with CdS and Zn(O,S) buffer layers

Alkali-fluoride post-deposition treatments (PDTs) of Cu(In,Ga)Se2 (CIGS) absorbers have repeatedly resulted in device efficiency improvements, observed mainly due to an open-circuit voltage (Voc) enhancement. Replacement of the CdS buffer layer with a higher band gap alternative can increase the short-circuit current density (Jsc) and also eliminate the use of Cd. In many alternative-buffer attempts, however, the Jsc gain was accompanied by a Voc loss, resulting in some degree of performance loss. In order to better understand the impact of RbF-PDT, we analyze a combination of experimental devices produced in the same in-line CIGS run with and without RbF-PDT in combination with chemical-bath-deposited CdS and Zn(O,S) buffers. Low-temperature current–voltage curves indicate a difference in Rb impact on the CIGS/CdS and CIGS/Zn(O,S) p-n junctions. For example, the diode-current barrier which creates a rollover often observed in RbF-treated CIGS/CdS current–voltage curves is significantly reduced for the CIGS/Zn(O,S) junction. Although the RbF-PDT had a positive impact on both junction partner combinations, the CIGS/Zn(O,S) devices' Voc and fill factor (FF) benefited stronger from the RbF treatment. As a result, in our samples, the Jsc and FF gain balanced the Voc loss, thus reducing the efficiency difference between cells with CdS and Zn(O,S) buffers.

Inverted rear-heterojunction GaInP solar cells using Te memory effect

Tellurium allows attaining heavy n-type doping levels in GaAs, which is suited to achieve very low contact resistivities in solar cells. Besides, it modifies the energy bandgap of MOVPE-grown GaInP by reducing the group-III sublattice ordering and presents a strong memory effect which induces residual n-type doping in subsequent layers, potentially detrimental to the performance of the solar cell. In this work, we present an inverted rear-heterojunction GaInP solar cell that employs a thick Te-doped GaInP layer as absorber, with a doping profile obtained exclusively by controlling the memory effect of Te coming from the preceding growth of a heavily doped GaAs contact layer. In this way, GaInP is partially disordered with the use of no additional surfactant, leading to an increase in the solar cell bandgap of around 35 meV as compared to traditional samples doped with silicon. In the proof-of-concept experimental devices developed so far, the use of a rear-heterojunction configuration and the bandgap increase results in a global open-circuit voltage enhancement of 109 mV. The photocurrent decreases by 1.32 mA/cm2, mostly due to the bandgap blue-shift, with about 0.35 mA/cm2 attributable to lower carrier collection efficiencies. These preliminary results are discussed by analyzing the I-V curve parameters and quantum efficiencies of a Te-doped rear-heterojunction, a Si-doped rear-heterojunction and a Si-doped front-junction solar cell. An additional advantage is that the emitter sheet resistance is reduced from 551 to 147 Ω/□, which offers potential for higher efficiencies through lower front grid shadowing factors, as demonstrated with the concentrator measurements presented.

Advanced partial nucleation for single-phase FA0.92MA0.08PbI3-based high-efficiency perovskite solar cells

To date, extensive research has been carried out, with considerable success, on the development of high- performance perovskite solar cells (PSCs). Owing to its wide absorption range and remarkable thermal stability, the mixed-cation perovskite FA x MA1− x PbI3 (formamidinium/methylammonium lead iodide) promises high performance. However, the ratio of the mixed cations in the perovskite film has proved difficult to control with precursor solution. In addition, the FA x MA1− x PbI3 films contain a high percentage of MA+ and suffer from serious phase separation and high trap states, resulting in inferior photovoltaic performance. In this study, to suppress phase separation, a post-processing method was developed to partially nucleate before annealing, by treating the as-prepared intermediate phase FAI-PbI2-DMSO (DMSO: dimethylsulfoxide) with mixed FAI/MAI solution. It was found that in the final perovskite, FA0.92MA0.08PbI3, defects were substantially reduced because the analogous molecular structure initiated ion exchange in the post-processed thin perovskite films, which advanced partial nucleation. As a result, the increased light harvesting and reduced trap states contributed to the enhancement of open-circuit voltage and short-circuit current. The PSCs produced by the post-processing method presented reliable reproducibility, with a maximum power conversion efficiency of 20.80% and a degradation of ~30% for 80 days in standard atmospheric conditions.