ZnO Nanorods as Antireflective Coatings for Industrial‐Scale Single‐Crystalline Silicon Solar Cells

In this work, both planar and textured, industrial scale (156 mm × 156 mm) single‐crystalline silicon (Si) solar cells have been fabricated using zinc oxide (ZnO) nanorods as antireflection coating (ARC). ZnO nanorods were grown in a few minutes via hydrothermal method within a commercially available microwave oven. Relative improvement in excess of 65% in the reflectivity was observed for both planar and textured Si surfaces. Through ZnO nanorods, effective lifetime (τ_eff) measurements were presented to investigate the surface passivation property of such an ARC layer. ZnO nanorods increased the τ_eff from 9 to 71 μs at a carrier injection level of 10¹⁵ cm^?3. Increased carrier lifetime revealed the passivation effect of the ZnO nanorods in addition to their ARC property. 33% and 16% enhancement in the photovoltaic conversion efficiency was obtained in planar and textured single‐crystalline solar cells, respectively. Our results reveal the potential of ZnO nanorods as ARC that can be deposited through simple solution‐based methods and the method investigated herein can be simply adapted to industrial scale fabrication.     

Realization of radial p-n junction silicon nanowire solar cell based on low-temperature and shallow phosphorus doping

A radial p-n junction solar cell based on vertically free-standing silicon nanowire (SiNW) array is realized using a novel low-temperature and shallow phosphorus doping technique. The SiNW arrays with excellent light trapping property were fabricated by metal-assisted chemical etching technique. The shallow phosphorus doping process was carried out in a hot wire chemical vapor disposition chamber with a low substrate temperature of 250°C and H₂-diluted PH₃ as the doping gas. Auger electron spectroscopy and Hall effect measurements prove the formation of a shallow p-n junction with P atom surface concentration of above 10²⁰ cm⁻³ and a junction depth of less than 10 nm. A short circuit current density of 37.13 mA/cm² is achieved for the radial p-n junction SiNW solar cell, which is enhanced by 7.75% compared with the axial p-n junction SiNW solar cell. The quantum efficiency spectra show that radial transport based on the shallow phosphorus doping of SiNW array improves the carrier collection property and then enhances the blue wavelength region response. The novel shallow doping technique provides great potential in the fabrication of high-efficiency SiNW solar cells.     

Impacts of Post-metallisation Processes on the Electrical and Photovoltaic Properties of Si Quantum Dot Solar Cells

As an important step towards the realisation of silicon-based tandem solar cells using silicon quantum dots embedded in a silicon dioxide (SiO₂) matrix, single-junction silicon quantum dot (Si QD) solar cells on quartz substrates have been fabricated. The total thickness of the solar cell material is 420 nm. The cells contain 4 nm diameter Si quantum dots. The impacts of post-metallisation treatments such as phosphoric acid (H₃PO₄) etching, nitrogen (N₂) gas anneal and forming gas (Ar: H₂) anneal on the cells’ electrical and photovoltaic properties are investigated. The Si QD solar cells studied in this work have achieved an open circuit voltage of 410 mV after various processes. Parameters extracted from dark I–V, light I–V and circular transfer length measurement (CTLM) suggest limiting mechanism in the Si QD solar cell operation and possible approaches for further improvement.     

A novel method for crystalline silicon solar cells with low contact resistance and antireflection coating by an oxidized Mg layer

One of the key issues in the solar industry is lowering dopant concentration of emitter for high-efficiency crystalline solar cells. However, it is well known that a low surface concentration of dopants results in poor contact formation between the front Ag electrode and the n-layer of Si. In this paper, an evaporated Mg layer is used to reduce series resistance of c-Si solar cells. A layer of Mg metal is deposited on a lightly doped n-type Si emitter by evaporation. Ag electrode is screen printed to collect the generated electrons. Small work function difference between Mg and n-type silicon reduces the contact resistance. During a co-firing process, Mg is oxidized, and the oxidized layer serves as an antireflection layer. The measurement of an Ag/Mg/n-Si solar cell shows that V _oc, J _sc, FF, and efficiency are 602 mV, 36.9 mA/cm², 80.1%, and 17.75%, respectively. It can be applied to the manufacturing of low-cost, simple, and high-efficiency solar cells.     

Preparation and characterization of Ag2ZnSn(S,Se)4 and its application in improvement of power conversion efficiency of Cu2ZnSn(S,Se)4-based solar cells

We fabricated high-quality n-type Ag₂ZnSnSe₄ (AZTSe) film with kesterite structure by using a simple solution method. A Cu₂ZnSnSe₄ (CZTSe)/AZTSe-based solar cell was designed and prepared by inserting AZTSe layer between CZTSe and CdS of the traditional CZTSe-based solar cell. Compared with the traditional device, an increase from 337 to 432 mV in open circuit voltage (V_oc) and an accompanying rise from 3.40% to 4.72% in power conversion efficiency (PCE) were observed. To well understand the PCE improvement of the CZTSe/AZTSe-based solar cells, we calculated the band alignments of CZTSe/AZTSe and CZTSe/CdS heterojunctions using first-principles calculations, demonstrating that the CZTSe/AZTSe and CZTSe/CdS interfaces have type-II and type-I band alignments, respectively. Moreover, the band offset of AZTSe/CdS is lager than the one of CZTSe/CdS. Combined with the calculation results, the mechanism of influence of the AZTSe on the PCE improvement is discussed in detail. Our conclusions show that the addition of the AZTSe layer is a potentially applicable method to obtain CZTSe-based solar cells with higher V_oc and PCE.     

Enhanced light absorption of amorphous silicon thin film by substrate control and ion irradiation

Large-area periodically aligned silicon nanopillar (PASiNP) arrays were fabricated by magnetic sputtering with glancing angle deposition (GLAD) on substrates coated by a monolayer of close-packed polystyrene (PS) nanospheres. The structure of PASiNP arrays could be manipulated by changing the diameter of PS nanospheres. Enhanced light absorptance within a wavelength range from 300 to 1,000 nm was observed as the diameter of nanopillars and porosity of PASiNP arrays increased. Meanwhile, Xe ion irradiation with dose from 1 × 10¹⁴ to 50 × 10¹⁴ ions/cm² was employed to modify the surface morphology and top structure of thin films, and the effect of the irradiation on the optical bandgap was discussed.

PACS code

81.15.Cd; 78.66.Jg; 61.80.Jh     

Novel Polymeric Metal Complexes for Dye Sensitizer: Synthesis and Photovoltaic Performances

Four novel polymeric metal complexes with a D–A–π–A motif, BDTT-PY-Cd, BDTT-PY-Zn, BDTT-PY-Cu and BDTT-PY-Ni, were designed, synthesized and characterized. These polymeric metal complexes were made up with Cd(II), Zn(II), Cu(II), Ni(II) complexes, thienylbenzo-[1,2-b:4,5-b'] dithiophene (BDTT) and the 8-quinolinol derivative, which were used severally as dye sensitzers’ auxiliary electron acceptors (A), electron donor (D) and π bridges as well as the acceptors (A). Under AM 1.5 irradiation (100 mW cm^?2), the devices of dye sensitized solar cells (DSSC) based on four polymer complexes exhibited short-circuit photocurrent densities (J_sc) of 17.45 mA cm^?2, 14.75 mA cm^?2, 13.94 mA cm^?2 and 12.00 mA cm^?2, as well as attractive power conversion efficiencies (PCE) of were 9.73%, 8.02%, 6.82% and 6.12%, respectively. The photovoltaic conversion efficiency (PCE) and short-circuit photocurrent density (J_sc) of BDTT-PY-Cd, BDTT-PY-Zn, BDTT-PY-Cu and BDTT-PY-Ni decrease in order because the radius and charge number of the metal ion affect the strength of the coordination bond between the metal ion and the ligand. These results provides a new way of development for efficient and stable dye sensitizers in the future.

     

Si/PEDOT:PSS core/shell nanowire arrays for efficient hybrid solar cells

A solution filling and drying method has been demonstrated to fabricate Si/PEDOT:PSS core/shell nanowire arrays for hybrid solar cells. The hybrid core/shell nanowire arrays show excellent broadband anti-reflection, and resulting hybrid solar cells absorb about 88% of AM 1.5G photons in the 300-1100 nm range. The power conversion efficiency (PCE) of the hybrid solar cell reaches 6.35%, and is primarily limited by direct and indirect interfacial recombination of charge carriers.     

TiO2/ZnO double-layer broadband antireflective and down-shifting coatings for solar applications

Making full use of sunlight in solar cells requires reducing the reflection of light and minimizing spectral mismatch. Here, a TiO₂/ZnO double-layer coating with both wider band antireflection and down-shifting performance was prepared. TiO₂ sols and ZnO nanoparticles were synthesized via the sol-gel method and then successively coated on the surface of the Si substrate by dip-coating. Computational simulations were used to obtain the optimal refractive index and thickness of the coatings. In the experiments, the thicknesses of the TiO₂ and ZnO coatings were adjusted by changing the lifting speed, and the refractive index of the TiO₂ and ZnO coatings were adjusted by adding the porosity inducing agent and varying the concentration of the solution. The TiO₂/ZnO coating reduces the reflectivity of the silicon substrate by 24.97% in the 400–1100 nm band, and the ZnO nanoparticles can convert light at approximately 345 nm–527 nm, reducing the spectral mismatch of the solar cell. The photocurrent of solar cells coated with TiO₂/ZnO coatings was markedly improved, with an increase of 29% in the average photocurrent at 300–800 nm. Herein, TiO₂/ZnO coatings have the potential to benefit the development of multifunctional coatings that are important for improving the efficiency of solar cells.     

Optimizing performance parameters of graphene–silicon and thin transparent graphite–silicon heterojunction solar cells

We investigated heterojunctions of Si with large-area high-quality monolayer and multi-layer graphene, as well as thin transparent graphite. We show that by controlling the transmittance and sheet resistance of large-area graphitic electrodes, it is possible to obtain solar cells with power conversion efficiency (PCE) exceeding 3% without any doping requirements. Our calculations indicate that such junctions can form extremely robust interfaces with near-100% internal quantum efficiency. Under optimized doping conditions, power conversion efficiencies increase almost universally by a factor of 2.5. Optimized conditions for reproducibly obtaining cells with PCE > 5% are presented, with the best PCE obtained ∼7.5% with short-circuit current density exceeding 24 mA/cm².     

Optimization of TiO2 paste concentration employed as electron transport layers in fully ambient air processed perovskite solar cells with a low-cost architecture

The optimization of thickness and surface roughness of the TiO₂ layer as an efficient electron transporting layer (ETL) plays a significant role on the performance improvement of perovskite solar cells (PSCs). In the present investigation, TiO₂ pastes synthesized with various concentrations under hydrothermal conditions were utilized to deposit the TiO₂ films of tunable porosities as the ETLs of PSCs. Also, the PSCs were fabricated with a structure of FTO/block-TiO₂ (b-TiO₂)/m-TiO₂/CH₃NH₃PbI₃ (MAPbI₃)/CuInS₂ (CIS)/carbon as a low-cost architecture. Moreover, the effect of the TiO₂ paste concentration was studied on the performances of PSCs under fully ambient conditions. The optimal TiO₂ layer was constructed with 20 wt% TiO₂ paste concentration, which resulted in the formation of a hole‐free, smooth, and compact ETL layer. The champion perovskite solar cell fabricated with the 20 wt% TiO₂ paste concentration showed the highest power conversion efficiency (PCE) of 13.09% (J_SC = 20.80 mA cm^?2, V_OC = 0.98 V and FF = 0.64) but the champion PSC device made with the 10 wt% TiO₂ paste exhibited the lowest PCE = 8.05% (J_SC = 19.83 mA cm^?2, V_OC = 0.91 V and FF = 0.45). These results illustrated that the optimal 20 wt% TiO₂ paste caused ～163% enhancement in the PCE of the device. Consequently, it could be suggested for application in fabrication of cost-effective and large scale PSCs.     

Air fabrication of SnO2 based planar perovskite solar cells with an efficiency approaching 20%: Synergistic passivation of multi-defects by choline chloride

Defects in the perovskite films impose a serious issue on the PCE and stability of the SnO₂ based planar perovskite solar cells (SP–PSCs). So far, most researches have focused on regulating the SnO₂/perovskite interface to improve performance. However, defect passivation of the perovskite/HTM interface is more significant and potential. Herein, the non-toxic and cheap choline chloride was performed to passivate multiple defects of the MAPbI₃/HTM interface in ambient atmosphere. An optimal PCE of 19.93% (the average PCE was 18.60%) was obtained for the passivated device. Furthermore, the effect and mechanism of choline chloride on the humid and thermal stability of the SP-PSCs was investigated in detail. The passivated device without encapsulation retained 91% of its initial efficiency after 20 days in humid environment (20 ± 5 °C, 55 ± 5% RH) and 95% of the initial value under heating for 7 cycles (85 °C). Chloride ions with smaller radius and larger electronegativity formed stronger ionic bonding with Pb²⁺ to passivate I^? vacancy defects, while choline ions passivated MA⁺ vacancies. This work not only provides guidance for fabrication of an efficient and stable device in air, but also opens an avenue to understanding of relation between stability and defects in the SP-PSCs.     

Absorption Enhancement in Ultrathin Structures Based on Crystalline-Si/Ag Parabola Nanocones Periodic Arrays with Broadband Antireflection Property

In this study, we examine the optical properties and unique features of a novel design of a parabola nanocone consisting of a homogenous shell-like cover layer of crystalline silicon (c-Si) and an Ag core which provides an enhanced absorption efficiency and significant photocurrent conversion during exposure to an incident light. Determining the geometrical sizes of the c-Si/Ag parabola nanocone, we designed an antireflection nanostructure based on certain arrays of investigated cone arrays on a GaAs substrate. We proved that the examined nanostructure shows a low percentage of reflectance of 6.24 % and a significant short current density of ~37.2 mA/m ² as well as broadband antireflection facility. This understanding paves the way for novel methods toward the use of a simple and two layer nanoparticle in designing efficient and high performance antireflection layers of photovoltaics and solar cells that are able to function over a wide range of spectrum.     

Effect of Al doped ZnO on optical and photovoltaic properties of the p-Cu2O/n-AZO solar cells

Metal oxide thin films have fared so well in the semiconductor industry because of their superior physical, electrical, and optical properties. The applications of these materials in solar cells, biosensors, biomedicine, supercapacitors, photocatalysis, luminous materials, and laser systems are becoming increasingly popular. In this study, the influence of Al concentration on Cu₂O/AZO heterojunction thin films was examined systematically. First, arrays of n-ZnO and AZO rods were produced on an ITO substrate using a hydrothermal technique at 140 °C. Then, using an alkaline cupric lactate solution, a thin films of p-Cu₂O were electrodeposited at 60 °C onto the ZnO arrays. The structure and morphology of the produced materials and the solar cells were studied using X-ray diffraction and scanning electron microscopy. The optical measurements demonstrate a shift in the absorption edge with increasing Al content. Solar cells have been created with a device structure of ITO/ZnO/Cu₂O/Al and ITO/Al-doped ZnO/Cu₂O/Al configurations. The power conversion efficiency (?) of the inorganic solar cell with 6% Al-doped ZnO is ? = 0.282%, which is greater than the ? of the ZnO-based solar cell (? = 0.17%).     

Facile synthesis of NiMn2O4 nanosheet arrays grown on nickel foam as novel electrode materials for high-performance supercapacitors

Nanostructured spinel NiMn₂O₄ arrays have been fabricated by a facile hydrothermal approach and further investigated as binder-free electrode for high-performance supercapacitors. Compared with Mn₃O₄, NiMn₂O₄ exhibited higher specific capacitances (662.5 F g⁻¹ and 370.5 F g⁻¹ in different electrolytes at the current density of 1 A g⁻¹) and excellent cycling stability (~96% capacitance retention after 1000 cycles) in a three-electrode system. Such a novel microstructure grown directly on the conductive substrate provided sufficient active sites for redox reaction resulting in their enhanced electrochemical behaviors. Their improved performances suggested that ultrathin sheet-like NiMn₂O₄ arrays on Ni foam substrate were a promising electrode material for supercapacitors.     

Boosting piezoelectric response of KNN-based ceramics with strong visible-light absorption

A series of (1 − x)(K_0.48Na_0.52)NbO₃-x(Bi_0.5Na_0.5)(Zr_0.55Ni_0.45)O_3-δ (KNN-BNZN) ceramics are designed to achieve excellent piezoelectric response along with narrow bandgap. The ceramics with x = 0.04 exhibit unprecedented piezoelectric coefficient d₃₃ ~ 318±10pC N⁻¹ in comparison with all reported narrow bandgap ceramics. A rhombohedral-orthorhombic-tetragonal (R-O-T) phase boundary is observed, indicating the formation of defect dipoles (Ni²⁺-) at morphotropic phase boundary region is desirable for piezo-/ferroelectric properties. In addition, a narrow bandgap ~2.5 eV along with gap states (~0.9 eV and ~1.6 eV) is obtained from the ceramics when x > 0.02, which can be persuasively explained by the schematic plot of bandgap splitting mechanism proposed in this work, where Ni 3d energy state plays a role as a scaffold in the process of electron transition. More importantly, largely enhanced photovoltaic performance of the ceramics is achieved under AM 1.5 irradiation. The NIR photoresponse property (maximum current density of ~100 nA cm⁻²) indicates such KNN-based ceramics with sub bandgap ~ 0.9 eV may even have potential to be applied in NIR light-activated devices. Our findings might pave way for the further development of piezoelectric/photoresponsive multifunctional devices.     

Nanostructured bilayer CuSCN@CuI thin films as efficient inorganic hole transport material for inverted perovskite solar cells

In this work, the development of bilayer CuSCN@CuI inorganic hole transport material by a simple electrochemical approach is demonstrated. The thickness and the morphology of the bilayer thin films are controlled by electrochemical potential and deposition time. Uniformly distributed triangle-shaped CuI nanosheets formation is observed at 2 min deposition time. Inverted perovskite solar cells are fabricated using electrochemically grown CuSCN@CuI bilayer and tested its photovoltaic performance. The maximum short circuit current density of 18.24 mA/cm² and open-circuit voltage of 1080 mV is achieved for uniformly distributed triangle-shaped CuI nanosheets grown at 2 min deposition time. The power conversion efficiency (PCE) of 15.58% is achieved with 1400 h of stability. The moderate thickness (~180–230 nm) of bilayer CuSCN@CuI nanostructures showed better charge transport and photovoltaic performance. The favourable band alignment of the designed CuSCN@CuI/perovskite/PC₆₁BM/Carbon delivers stable open-circuit voltage than the earlier reports. The optimized bilayer CuSCN@CuI nanostructure with carbon back contact showed improved device stability.     

Novel Hybrid Nanorod Carriers of Fluorescent Hydroxyapatite Shelled with Mesoporous Silica Effective for Drug Delivery and Cell Imaging

Development of biocompatible multifunctional nanocarriers is necessary for the success of theranostics. Here, we report a novel hybrid nanorod with self‐fluorescent property, high drug loading capacity, and good biocompatibility. Fluorescent hydroxyapatite (fHA) nanorod was ensheathed with mesoporous silica (mSi). The mSi shell was uniformly layered and was tunable in thickness (10–30 nm) over the fHA nanorod. Highly mesoporous structure of mSi shell facilitated the loading of a large quantity of biological molecules, as confirmed with fluorescein isothiocynate; ~1% loading for fHA increased to ~10% loading for fHA@mSi. The self‐fluorescent property of the fHA resulting from CO₂^.? radicals was well preserved in the fHA@mSi hybrid, as analyzed by photoluminescence and electron paramagnetic resonance property. Cellular toxicity of the fHA@mSi hybrid nanorod showed favorable cell viability (>90% viability of control) up to a concentration of ~40 μg/mL. Intracellular uptake rate of the hybrid nanorod was as high as 80–90%, as analyzed by fluorescent‐assisted cell sorter. Results demonstrate the newly developed fHA@mSi nanocarriers have great potential for the effective loading of therapeutic molecules and delivery within intracellular compartments in concert with a capacity for in situ imaging.     

A copolymer based on benzo[1,2-b:4,5-b′]dithiophene and quinoxaline derivative for photovoltaic application

A D–A–D copolymer (PBDTQx) with a bandgap of 1.78 eV, containing alkoxy-substituted benzo[1,2-b:4,5-b′]dithiophene (BDT) as donor and quinoxaline derivative (Qx) as acceptor, was synthesized by Stille coupling reaction. In order to study the photovoltaic property of PBDTQx, polymer solar cells (PSCs) were fabricated with PBDTQx as the electron donor blended with [6,6]-phenyl-C61-butyric acid methyl ester (PC₆₁BM) as the electron acceptor. The power conversion efficiency (PCE) of PSC was 1.01% for an optimized PBDTQx: PC₆₁BM ratio of 1:5, under the illumination of AM 1.5, 100 mW/cm². The results indicated that PBDTQx was a promising donor candidate in the application of polymer solar cells.     

Well‐functioned photovoltaics based on nanofibers composed of PBDT‐TIPS‐DTNT‐DT and graphenic precursors thermally modified by polythiophene,polyaniline and polypyrrole

Reduced graphene oxide nanosheets modified by conductive polymers including polythiophene (GPTh), polyaniline (GPANI) and polypyrrole (GPPy) were prepared using the graphene oxide as both substrate and chemical oxidant. UV–visible and Raman analyses confirmed that the graphene oxide simultaneously produced the reduced graphene oxide and polymerized the conjugated polymers. The prepared nanostructures were subsequently electrospun in mixing with poly(3‐hexylthiophene) (P3HT)/phenyl‐C71‐butyric acid methyl ester (PC₇₁BM) and poly[bis(triisopropylsilylethynyl)benzodithiophene‐bis(decyltetradecylthien)naphthobisthiadiazole] (PBDT‐TIPS‐DTNT‐DT)/PC₇₁BM components and embedded in the active layers of photovoltaic devices to improve the charge mobility and efficiency. The GPTh/PBDT‐TIPS‐DTNT‐DT/PC₇₁BM devices demonstrated better photovoltaic features (J_sc = 11.72 mA cm^?2, FF = 61%, V_oc = 0.68 V, PCE = 4.86%, μ_h = 8.7 × 10^?3 cm² V^–1 s^?1 and μ_e = 1.3 × 10^?2 cm² V^–1 s^?1) than the GPPy/PBDT‐TIPS‐DTNT‐DT/PC₇₁BM (J_sc = 10.30 mA cm^?2, FF = 60%, V_oc = 0.66 V, PCE = 4.08%, μ_h = 1.4 × 10^?3 cm² V^–1 s^?1 and μ_e = 8.9 × 10^?3 cm² V^–1 s^?1) and GPANI/PBDT‐TIPS‐DTNT‐DT/PC₇₁BM (J_sc = 10.48 mA cm^?2, FF = 59%, V_oc = 0.65 V, PCE = 4.02%, μ_h = 8.6 × 10^?4 cm² V^–1 s^?1 and μ_e = 7.8 × 10^?3 cm² V^–1 s^?1) systems, assigned to the greater compatibility of PTh in the nano‐hybrids and the thiophenic conjugated polymers in the bulk of the nanofibers and active thin films. Furthermore, the PBDT‐TIPS‐DTNT‐DT polymer chains (3.35%–5.04%) acted better than the P3HT chains (2.01%–3.76%) because of more complicated conductive structures. © 2019 Society of Chemical Industry