Effect of KOH treatment on structural and photovoltaic properties of ZnO nanorod arrays

ZnO nanorod arrays （NRs） were synthesized on the fluorine-doped SnO2 transparent conductive glass （FTO） by a simple chemical bath deposition （CBD） method combined with alkali-etched method in potassium hydroxide （KOH） solution. X-ray diffraction （XRD）, scanning electron microscopy （SEM） and current-voltage （I-V） curve were used to characterize the structure, morphologies and optoelectronic properties. The results demonstrated that ZnO NRs had wurtzite structures, the morphologies and photovoltaic properties of ZnO NRs were closely related to the concentration of KOH and etching time, well-aligned and uniformly distributed ZnO NRs were obtained after etching with 0.1 mol/L KOH for 1 h. ZnO NRs treated by KOH had been proved to have superior photovoltaic properties compared with high density ZnO NRs. When using ZnO NRs etched with 0.1 mol/L KOH for 1 h as the anode of solar cell, the conversion efficiency, short circuit current and open circuit voltage, compared with the unetched ZnO NRs, increased by 0.71%, 2.79 mA and 0.03 V, respectively.

Organic Photovoltaic Properties Based on Oligothiophenes

The ITO/5T/PCH/Al1 device has a short circuit current of 3.4 mA/cm^2, an open circuit voltage of 2.1 V, fill fact of 27.5 % and photoelectric conversion efficiency of 2.5 %.

Organic photovoltaic devices with high open-circuit voltage based on oligothiophene derivatives

For the purpose of developing organic photovoltaic devices with good performance characteristics, we have fabricated two devices using 4T-CHO, 5T-CHO and PTCDA. The ITO/4T-CHO/PTCDA/Al device has a Voc of 2.45 V and photoelectric conversion efficiency of 2.76%. The ITO/ST-CHO/PTCDA/Al device has a Voc of 2.1 3V and photoelectric conversion efficiency of 2.90%. The two devices have higher Voc （2.45 and 2.13 V）. It is possible that intennolecular hydrogen bonding between -CHO group of nT-CHO and carboxylic dianhydride of PTCDA contribute to enhance the efficiency by promoting interracial electron transfer and eliminating the subconducting band trap sites.

6AZO-CONTAINING SELF-ASSEMBLY ULTRA-THIN FILMS AND THEIR PHOTOVOLTAIC PROPERTIES

A kind of azo-containing resin(Azo-R)was synthesized by a simple way through the coupling reaction of 2-nitro-N-methyldiphenylamine-4-diazoresin(NDR)with phenol,and a new covalentely attached multilayer film from Azo-R asH-donor and photosensitive diazoresin,diphenylamine-4-diazoresin(DR)as H-acceptor via H-bonding attraction by self-assembly technique has been fabricated.Following the decomposition of diazonium group of DR under exposure to UVlight,the H-bonds between the layers of the film convert to covalent bonds and the film becomes very stable toward polarsolvents or electrolyte aqueous solutions.Thus the UV-irradiated azo-containing films can be used to measure photocurrentin a conventional three-electrode photoelectrochemical cell using KCl as supporting electrolyte.It was confirmed that theazo-containing multilayer film is responsible for the photocurrent generation.

Significant Enhancement in Photovoltaic Performances for C217-based Dye Sensitizers via Introducing Electron-withdrawing Substituents: a Theoretical Study

Dye-sensitized solar cells(DSSCs) are one of the most promising photovoltaic technologies, and the development of efficient dye sensitizers, especially inexpensive metal-free organic dyes, is always crucial for fabricating new DSSC devices. In this paper, a series of novel metal-free dyes with the D-A-π-A structure were designed by introducing electron-withdrawing substituents into the C217 molecular skeleton, and then their photovoltaic parameters were predicted by means of density functional theory(DFT) and time-dependent DFT(TD-DFT) calculations in combination with the Marcus charge transfer model. Our results showed that compared with C217, the introduction of trifluoromethyl(-CF3), cyano(-CN), and nitryl(-NO2) can efficiently narrow the HOMO-LUMO gap, and remarkably enhance the dye’s sunlight harvesting. With the(TiO2)38 cluster model, the photoelectric conversion efficiency(PCE) for the C217 dye was predicted to be up to 9.82%, which is in good agreement with the measured value(9.6%~9.8%), suggesting that our scheme used in this paper is reliable. Based on the same method, the PCE of most designed dyes was estimated to exceed over 10%, denoting that the molecular design strategy recommended by us in this work is reasonable. Especially, the PCE values of the dye 1, 4, and 6 were found to be as high as 14.75%, 16.02% and 15.75% respectively, suggesting that these three dyes are potential candidates as efficient sensitizers, and are worth further experimental study.

Correlation between the Low-Temperature Photoluminescence Spectra and Photovoltaic Properties of Thin Polycrystalline CdTe Films

A dominant intrinsic luminescence band, which is due to the surface potential barriers of crystalline grains, and an edge doublet, which arises as an LO-phonon repetition of the e-h band, has been revealed in the low-temperature photoluminescence spectra of fine-grained obliquely deposited films. Doping film with In impurity leads to quenching of the doublet band, while further thermal treatment causes activation of the intrinsic band, the half-width and the blue shift of the red edge of which correlates with the maximum value of anomalously high photovoltage generated by the film.

Rectifying and photovoltaic properties of ZnCo_2O_4/Si heterostructure grown by pulsed laser deposition

ZnCo2O4/Si heterostructures have been fabricated by a pulsed laser deposition method, and their transport behaviors and photovoltaic properties have been characterized. The ZnCo2O4/Si heterostructures show a good rectifying behavior at five different temperatures ranging from 50 K to 290 K. The measurements of the photovoltaic response reveals that a photovoltage of 33 mV is generated when the heterostructures are illuminated by a 532 nm laser of 250 mW/cm^2 and mechanically chopped at 2500 Hz. Both the photocurrent and the photovoltage clearly increase with the increase of the laser intensity at room temperature. However, the heterostructures＇ photovoltage peak decreases with the increase of the temperature. This work may open new perspectives for ZnCo2O4/Si heterostructure-based devices.

First principles study of the electronic structure and photovoltaic properties ofβ-CuGaO2 with MBJ+U approach

Based on the density functional theory,the energy band and electronic structure ofβ-CuGaO2 are calculated by the modified Becke-Johnson plus an on-site Coulomb U(MBJ+U)approach in this paper.The calculated results show that the band gap value ofβ-CuGaO2 obtained by the MBJ+U approach is close to the experimental value.The calculated results of electronic structure indicate that the main properties of the material are determined by the bond between Cu-3 d and O-2p energy levels near the valence band ofβ-CuGaO2,while a weak anti-bond combination is formed mainly by the O-2p energy level and Ga-4 s energy level near the bottom of the conduction band ofβ-CuGaO2.Theβ-CuGaO2 thin film is predicted to hold excellent photovoltaic performance by analysis of the spectroscopic limited maximum efficiency(SLME)method.At the same time,the calculated maximum photoelectric conversion efficiency of the ideal CuGaO2 solar cell is 32.4%.Relevant conclusions can expandβ-CuGaO2 photovoltaic applications.

Near-infrared double-cable conjugated polymers based on alkyl linkers with tunable length for single-component organic solar cells

The photovoltaic properties of double-cable conjugated polymers are significantly influenced by the length of the alkyl linkers that connect donor backbones and acceptor side units. In this study, a series of 2-(3-oxo-2,3-dihydroinden-1-ylidene)malononitrile(IC)-based double-cable polymers with alkyl linkers ranging from C_8H_(16)to C_(16)H_(32)(Px, x = 8, 10, 12, 14, 16) were synthesized for single-component organic solar cells(SCOSCs). Among these, the linker length x = 12(P12) is found to optimize the power conversion efficiencies(PCEs) in SCOSCs. Specifically, PCEs increase from P8 to P12 and then decline from P12to P16. Detailed investigations of optical absorption, charge transport, and morphology provide insights into the underlying factors contributing to these PCE variations. The findings indicate that the exceptional photovoltaic properties observed in P12 can be attributed to three key factors: A delicate balance between enhanced charge separation facilitated by the increased spacer length and reduced crystallinity resulting from longer spacers, higher charge mobilities, and well-balanced hole/electron transport characteristics. This study highlights the critical role of linker length in determining the photovoltaic properties of double-cable conjugated polymer-based SCOSCs and offers valuable guidance for the design of novel double-cable conjugated polymers.

Theoretical Prediction on Photovoltaic Properties of 4CI-BPPQ/ PC61BM System via Density Functional Theory Calculations

Designing and synthesizing high-performable electron donor materials are very important for fabricating organic solar cell devices with high power conversion efficiency （PCE）. In this work, quantum chemical and molecular dynamics calculations coupled with the Marcus-Hush charge transfer model were used to investigate the photovoltaic properties of 4Cl-BPPQ/PC61BM. Results reveal that 4Cl-BPPQ/PCrlBM system theoretically possesses a large open-circuit voltage （1.29 V）, high fill factor （0.90）, and over 9% PCE. Moreover, calculations also reveal that the 4Cl-BPPQ/PC61BM system has a middle-sized exciton binding energy （0.492 eV）, but relatively small charge-dissociation and charge-recombination reorganization energies （0.345 eV and 0.355 eV）. Based on the 4CI-BPPQ/PC61BM complex, the charge-dissociation rate constant, kdis, is estimated to be as large as 6.575× 10^12 s^-1, while the charge-recombination one, krec, is very small （〈 1.0 s^-1） under the same condition due to the very small driving force （AGree=-1.900 eV）. In addition, by means of an amorphous cell containing one hundred 4C1-BPPQ molecules, the hole carrier mobility of 4CI-BPPQ solid is estimated as high as 3.191 × 10^-3 cm^2·V^-1·s^-1. In brief, our calculation shows that 4Cl-BPPQ/PC61BM system is a very promising organic solar cell system, and is worth of making further device research by experiments.

Photovoltaic Properties of Thermally-Grown Selenium-Doped Silicon Photodiodes for Infrared Detection Applications

In this work, the photovoltaic properties of selenium-doped silicon photodiodes were studied. Influence of illumination of the impurity absorption range on the current-voltage and spectral characteristics of the fabricated device were considered. The photoresponse dependencies on the electric intensity, current, and radiation power at the sample were observed. Results obtained in this work showed that the current-sensitivity of the fabricated structures at the forward bias was rather higher than that of photoresistors. The photosensitivity and detectivity were up to 2.85 × 10^- 6 W.Hz^-1/2 and 2.1 × 10^11 cm.Hz^1/2w^-1, respectively.

Effect of Cl doping amount on the microstructure,photovoltaic properties and ferroelectric properties of Bi-based lead-free perovskite

Organic-inorganic hybrid perovskites with 3D perovskite structure have gained much attention as light harvesting materials in thinfilm photovoltaics.This is because of their outstanding light-absorption characteristics,charge-transport dynamics and their simple processability using lab-scale solution and vapor phase deposition techniques.However,the inherent instability and lead toxicity of lead-based PSCs are the major problems at present.Recent studies have shown that the(CH_(3)NH_(3)T_(3)Bi_(2)I_(9)(MBI)0D bismuth-based compound can be used as an optical absorption layer in solar cells.In this paper,the(CH_(3)NH_(3)T_(3)Bi_(2)I_(9)was doped with Cl
and a series of(CH_(3)NH_(3)T_(3)Bi_(2)I_(9-x)Cl_(x)films were prepared.The effects of different doping amounts on the microstructure,photovoltaic properties and ferroelectric properties were systematically investigated.Scanning electron microscope(SEM)and Atomic force microscope(AFM)analysis showed that with the increase of doping content,the density of the films increased and the roughness decreased.The photoelectric conversion efficiency of(CH_(3)NH_(3)T_(3)Bi_(2)I_(9-x)Cl_(x)raises with the increase of doping content.For example,the photoelectric conversion efficiency of(C_(H)3NH_(3)T_(3)Bi_(2)I_(3)Cl_(6)is 0.473%.We find that the leakage current descends into the increase in doping content,which may be due to the increase in the film density and the decrease of porosity.These research results have a positive effect on the development of Bi-based lead-free perovskite.

Recent Progress of Inorganic Hole-Transport Materials for Perovskite Solar Cells

Perovskite solar cells (PSCs) have achieved significant progress in the past decade and a certified power conversion efficiency (PCE) of 26.0% has been achieved.The widely used organic hole transport materials (HTMs) in PSCs are typically sensitive to the moisture environment and continuous light exposure.In contrast,the inorganic HTMs benefiting from their outstanding merits,such as excellent environmental stability,are considered as alternatives and have attracted much attention in PSCs.In this review,we provide a comprehensive summary of the fundamental properties and recent progress of inorganic HTMs in n-i-p and p-i-n structured PSCs.Additionally,we emphasize the importance of inorganic HTMs in the development of highly efficient and stable PSCs.

A-DA′D-A non-fullerene acceptors for high-performance organic solar cells

Since the world-record power conversion efficiency of 15.7%was achieved for organic solar cells(OSCs)in 2019,the newly developed non-fullerene acceptor(NFA)Y6 with an A-DA′D-A structure(A denotes an electron-accepting moiety,D denotes an electron-donating moiety)has attracted increasing attention.Subsequently,many new A-DA′D-A NFAs have been designed and synthesized,and the A-DA′D-A NFAs have played a significant role in the development of high-performance non-fullerene organic solar cells(NF-OSCs).Compared with the classical A-D-A-type acceptors,A-DA′D-A NFAs contain an electrondeficient core(such as benzothiadiazole(BT),benzotriazole(BTA),quinoxaline(Qx),or their derivatives)in the ladder-type fused rings to fine-tune the energy levels,broaden light absorption and achieve higher electron mobility of the NFAs.This review emphasizes the recent progress on these emerging A-DA′D-A(including Y-series)NFAs.The synthetic methods of DA′D-fused rings are introduced.The relationships between the chemical structure of the A-DA′D-A NFAs and the photovoltaic performance of the corresponding OSCs are summarized and discussed.Finally,issues and prospects for further improving photovoltaic performance of the OSCs are also proposed.

Slight Structural Disorder in Bithiophene-based Random Terpolymers with Improved Power Conversion Efficiency for Polymer Solar Cells

A series of random terpolymers P2-P5 were designed and synthesized by randomly embedding 5 mol%, 10 mol%, 15 mol% and 25 mol% feed ratios of low cost 2,2-bithiophene as the third monomer to the famous donor-acceptor （D-A） type copolymer PTBT-Th （P1）. All polymers showed similar molecular weight with number-average molecular weight （Mn） and weight-average molecular weight （Mw） in the range of （59-74） and （93-114） kg·mol-1, respectively, to ensure a fair comparison on the structure-property relationships. Compared with the control copolymer PTBT-Th, the random terpolymers exhibited enhanced absorption intensity in a wide range from 400 nm to 650 nm in both solution and film as well as in polymer/PC71BM blends. From grazing incident wide-angle X-ray diffraction （GIWAXS）, compared with the regularly alternated copolymer PTB7-Th, the random terpolymers demonstrated mild structural disorder with reduced （100） lamellar stacking and slightly weakened （010） π-π stacking for the polymers as well as slightly reduced PC71BM aggregation in polymer/PC71BM blends. However, the measured hole mobility for terpolymers （（1.20-3.73） × 10 -4 cm2·V-1·s-1） was evaluated to be comparable or even higher than 1.35 × 10 -4 cm2·V-1 ·s-1 of the alternative copolymer. Enhanced average power conversion efficiency （PCE） from 7.35% to 8.11% and 7.79% to 8.37% was observed in both conventional and inverted device architectures from copolymer P1 to terpolymers P4, while further increasing the 2,2-bithiophene feed ratio decreased the PCE.

Dye-sensitized solar cells based on functionalized truxene structure

Three new metal-free organic dyes （TX1, TX2 and TX3） based on truxene core structure, with triphenylamine as the electron donor, thiophene as the n spacers, and cyanoacetic acid or rhodanine-3- acetic acid as the electron acceptor are designed and synthesized. Their UV-vis absorption spectra, electrochemical and photovoltaic properties were investigated. The cyanoacrylic acid is verified to be a better acceptor unit （meanwhile the anchoring group） compared to the rhodanine-3-acetic acid. And also, two anchoring groups in TX2 could provide stronger adsorption ability on the TiO2 surface. In addition, the EIS results indicate a slower charge recombination processes for TX2. As a result, dye TX2 bearing two cyanoacetic acid outperforms the other two dyes, exhibiting the photo-conversion efficiency of 2.64%, with Jsc = 5.09 mAcm^-2, Voc = 729 mV, FF = 71.1.

The effect of dispersion of TiO_2 nanoparticles on preparation of flexible dye-sensitized photoanodes

Generally, nanoparticles are easy to aggregate due to their nano sizes, which influence the physical and chemical properties. In this work, a dispersion treatment of the TiO2 nanoparticles with different average sizes was employed to improve the disper- sion of TiO2 nanoparticles, in order to prepare flexible photoanodes for dye-sensitized solar cells （DSCs） with novel photovol- talc properties at a low temperature. The effects of dispersion treatment on the dispersion of TiO2 nanoparticles, including the viscosities of the binder-free TiO2 paste, the morphologies and textural properties of nanoparticle-TiO2 films, and the photo- voltaic properties of the flexible DSCs, were investigated. Flexible indium-tin oxide （ITO）-coated polyethylene naphthalate （PEN） substrates with sputter deposited Pt were employed as the transparent flexible counter electrodes. A short-circuit photo- current density of 9.62 mA·cm^-2, an open-circuit voltage of 0.757 V, a fill factor of 0.589 and an overall light-to-energy con- version efficiency of 4.29% for the flexible DSCs under AM1.5 illumination of 100 mW·cm^-2 were obtained with dispersion treatment. A 30.8% increment of the energy conversion efficiency for DSCs made by dispersion treatment was obtained com- pared with that made without dispersion treatment.