Photovoltaic materials
Silicon-based solar cells occupy the largest share of photovoltaic industry, but their efficiency decreases due to the high operating temperatures under sunlight, which reduces their power output. Thus, cooling the silicon based solar cells under irradiation is very important. In this study, Sb-doped tin oxide ATO thin films, working as the cover plate of silicon-based solar cells, were deposited on glass substrates by Sol-Gel spin-coating method, with SnCl2·H2O and SbCl3 as raw materials. Influence of Sb doping and film thickness on the heat shielding property and the performance of solar cells were investigated. As a result, the shielding performance of the ATO films was improved with the increase of the thickness, while its transmittance reduces with the increase of the thickness. Compared with ordinary glass cells, temperature of solar cells with spin-coated ATO thin films of 1 to 4 layers decreases by 2.7 ℃, and their efficiency keeps over 10.79% after being irradiated by AM1.5 solar simulator for 30 min. What’s more, the ATO doped with 10mol% Sb performs the best thermal insulation. Efficiency of silicon solar cell covered with 10mol% Sb-doped ATO film increases by 0.43% as compared with blank after being irradiated by solar simulator for 30 min.
Ag2Se quantum dots (QDs) was synthesized by co-deposition method which was further applied as co-sensitizer in solid-state dye-sensitized solar cells (DSSCs). The effects of different sensitization methods of Ag2Se QDs (TiO2/N719/QDs, TiO2/QDs/N719) and sensitization time (0-5 h) on the performance of QDs/dye co-sensitized solar cells were studied. Structure and optical properties of Ag2Se QDs were characterized by transmission electron microscopy (TEM) and ultraviolet-visible spectroscopy (UV-Vis). Furthermore, the transmission of charge carriers of solar cell devices was characterized by photo-modulated photocurrent/voltage spectrum (IMPS/VS) and electrochemical impedance spectra (EIS). It was found that the device with TiO2/QDs/N719 showed higher incident photon-to-current efficiency (IPCE) and photoelectric efficiency than those of TiO2/N719/QDs, which was due to the fact that TiO2/QDs/N719 photoanode adsorbed more QDs and dyes. With the extension of Ag2Se QDs sensitization time, the photovoltaic properties of DSSCs firstly ascended and then descended, achieving the highest photoelectric conversion efficiency 3.97%. The incorporation of Ag2Se QDs could effectively promote the electron transport and inhibit the electron-hole recombination, which benefited from a blocking layer that QDs served in device. As sensitization time prolonged over 2 h, the photovoltaic performances of device deteriorated, which was attributed to the augmented trap sites in Ag2Se QDs layer.
All-inorganic cesium lead halide CsPbX3 (X = Cl, Br, I) perovskite materials emerged as a rising star in the area of optoelectronics since 2015, due to its excellent photoelectric properties and environmental stability. Substantial progresses were made in the application of many electronic and optoelectronic devices, which attracted wide attention from the scientific community. This paper mainly reviews the latest research progress of cesium lead halide perovskite based planar heterojunction LED, where the structure and working principle of LED devices are briefly introduced. In addition, the classification and summarization of some optimization strategies for improving luminescence performance and working stability of LED devices are emphatically suggested, and the development trend of stable and efficient inorganic perovskite based planar heterojunction LED is finally prospected.
As the continuous development of the photovoltaic industry and the flat panel display devices, the demand for transparent electrodes is increasing rapidly. The most commonly used transparent conductive material, ITO, was criticized for its brittleness, which limited its application in the up-and-coming market. Cu nanowire transparent electrodes acts as promising candidate for the new generation of transparent electrodes due to their superior conductivity, low cost, easy accessibility and high flexibility. The synthesis of Cu nanowires and their application in transparent electrodes has drawn lots of attention. Progresses have been made in recent years. A comprehensive elaboration of the controllable synthesis of Cu nanowires through liquid synthesis methods and the mechanism behind them, the fabrication and post-treatment methods of Cu nanowire electrodes, the application of Cu nanowire electrodes in photovoltaic devices, transparent heaters and flexible devices are given. The trends of Cu nanowire electrodes is proposed.
As a type of novel thin film solar cells, perovskite solar cells develope sharply within a decade, which efficiency has approached to that of the commercial silicon solar cells. However, its poor stability in the air has limited the further practical application. Herein, we achieve uniform sable perovskite films under open environment by adding some poly 4-vinylpyridine (PVP). The morphology, structure and performance test results show that the perovskite films added with PVP were more compact and uniform than the bare one. Moreover, the assembled solar cell with 0.4wt% PVP exhibited highly reproducible efficiencies up to 13.07%, much higher than that of 6.09% for the controlled one. When restored in the air with approximately 50% relative humidity in the absence of encapsulation, its efficiency decay time to a half from 3 d for bare one extended to 3 w. However, high PVP additives result in incomplete reaction between PbI2 and CH3NH3I. If the above mentioned process is further optimized, is expected to be applied to the large-scale preparation of more stable perovskite film.
Organic-inorganic hybrid halide perovskites have attracted a huge amount of research interest and arised new research upsurge due to its broad absorption range, low trap density, low carrier recombination, and other excellent optoelectronic properties. Perovskite solar cells have shown great potential for application with maximum power conversion efficiencies evolving from 3.8% to 22.1% in just a few years. Single crystal has extremely low defect density and minimal interface defect than polycrystalline materials. Several research groups successfully cultivated large-sized perovskite single crystals, finding that perovskite single crystal is an ideal material for design and fabrication of photovoltaic devices for better light-response than polycrystalline and thin-film materials. Among all kinds of perovskite materials, CH3NH3PbI3 is one of the most widely studied and applied perovskite materials. This paper reviews the study of CH3NH3PbI3 single crystal recently, introducing its structure and superior characteristics. Particularly, growth methods and applications of perovskite single crystals are highlighted. Finally, the development trend of perovskite single crystals is prospected.
Recovering Si material from the degraded solar cells is significant for environmental protection and material recycling. In this tudy, the optimal conditions for recycling degraded solar cells by chemical etching and ultrasonic cleaning were investigated. The samples were tested by EDS, SEM and XPS, The results showed that Al electrodes were completely removed from cells by reaction with 10wt% NaOH solution for 18 min, with less silicon corrosion lost. After that, Ag electrodes were completely exfoliated from the cells by ultrasonic cleaning (40 kHz) for 20 min. Si3N4 film was thoroughly eliminated after the cells were etched with 40wt% HF solution for 10 min, which was proved to be the optimal reaction time. A quantitative experiment was performed in this study with 8. 9068 g cells. The results show that the recycling mass of Al electrodes, Ag electrodes and Si wafers are 1.1102 g, 0.0766 g and 7.7169 g, respectively.
Cobalt sulfide nanomaterials are considered as important counter electrode materials for dye-sensitized solar cells. A potential reversal electrodeposition technique was applied to fabricate transparent cobalt sulfide film with fluorine-doped tin oxide glass as substrate. The experimental results demonstrate that the surface morphology of cobalt sulfide films is mainly dependent on the pH value of plating solution. The thickness of cobalt sulfide films can be effectively controlled by electrodeposition cycles. Then, cobalt sulfide films were used as counter electrodes of dye-sensitized solar cells. Electrochemical measurements prove that cobalt sulfide counter electrodes exhibit high electrocatalytic activity. In particular, under electrodeposition condition of pH 7.2 and 12 cycles, cobalt sulfide counter electrode composed of the nanosheet structure exhibits higher electrocatalytic activity than platinum electrode, due to the increase of electrocatalytic active sites. Meanwhile, remarkable photoelectrical conversion efficiency of the dye-sensitized solar cell based on cobalt sulfide counter electrode is up to 7.26% with an average value of 7.18% for ten devices, which is higher than that of the dye-sensitized solar cell equipped with platinum electrode (6.94%).
In this paper, the band structure of Zn1-xMgxO(ZMO) alloy with different Mg compositions by using first-principles calculations with GGA+U method was studied. The calculation results show that position of conduction band offset and Fermi level of Zn1-xMgxO move towards the vacuum level while the band gap becomes wider with the increasing Mg concentration. Based on theoretical calculation results of ZMO, ZMO/CdTe, CdS/CdTe solar cells were modeled using SCAPS software and its device performances were simulated and analyzed in detail. The results indicate that the conversion efficiency of CdTe solar cell with ZMO is higher than that of solar cell with CdS due to the high open circuit voltage and short circuit current density when x in Zn1-xMgxO is in the range of 0-0.125. Efficiency of CdTe solar cells with ZMO reaches 18.29% because the recombination decreases obviously resulting from appropriate conduction band offset about 0.13 eV at ZMO/CdTe interface. These data provide a theoretical guidance for design and fabrication of high efficiency CdTe solar cells.
Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) film is commonly used as hole transport layer in planar perovskite solar cells (PSCs). To further strengthen the charge transport within PEDOT:PSS film and boost the growth of the perovskite crystal on PEDOT:PSS film, carbon nanotubes (CNTs) and dimethyl sulfoxide (DMSO) were simultaneously used as additives to prepare the co-modified film of CNT-DMSO-PEDOT:PSS. Results demonstrate an advantageous cooperative effect of CNTs and DMSO on the co-modified film. The dispersed CNTs with a grid-like structure throughout PEDOT:PSS matrix plays dual roles: to promote the perovskite crystal growth on co-modified surface and to reduce the sheet resistance of the co-modified film, while DMSO improves the conductivity of the co-modified film and controls the loss of CNTs from the co-modified film. Due to the cooperative effect, co-modified film is significantly more capable to collect, transport charges and enhance the perovskite layer growth with larger grains on its surface than that with pristine PEDOT:PSS film or PEDOT:PSS films modified by a single additive of CNT or DMSO, CNT-PEDOT:PSS or DMSO-PEDOT:PSS. Meanwhile, the co-modified film maintains high transparency with a transmittance of 88.8% at 550 nm. As a result, the PSCs of co-modified film has a hig power conversion efficiency of 5.75% in contrast to the devices based on the CNT-PEDOT:PSS (3.01%), DMSO-PEDOT:PSS (2.03%) and pristine PEDOT:PSS (1.30%) films.
Quantum dots sensitized solar cells (QDSCs) play a key role in the new generation photovoltaic devices due to their low cost and easy fabrication process. The absorption spectrum of quantum dots can be tailored by controlling grain size, and multi-exaction generation. QDSCs using inorganic compound QDs replaces the dye as a sensitizer, which is able to solve the stability of the dye sensitized solar cells. However, further improvement of the conversion efficiency of QDSCs is still a major issue for their application. Recently, tailoring electronic properties of the counter electrode(CE) in QDSCs using different materials has been considered as a promising way to improve photovoltaic performance of QDSCs. This article reviewed the quite recent progress of CE in QDSCs based on synthesis method, surface microtopography and crystal structure. This review gave a panorama of metal chalcogenides, composite materials, hybrid materials, muti-component metal chalcogenides, conductive polymers, and carbon CE materials for QDSCs, while the influence of CE materials on the charge transfer impedance, the electron transport process, catalytic properties, and I-V characteristics was stressed in detail. Finally, an outlook on the future challenges and prospects of novel materials as the CE for QDSCs were also briefly put forward.
ZnO nanosheets/nanoparticles/microspheres composite photoanodes were synthesized in two steps. ZnO nanosheets photoanodes on Ti foil substrates were first prepared with hydrothermal synthesis method, on which ZnO nanoparticles and microspheres were deposited by using chemical bath deposition method. The corresponding photoanodes were assembled into flexible dye-sensitized solar cells (FDSSCs). Effect of Ti foil substrates pretreatment methods and chemical bath deposition process on the properties of ZnO thin films and devices were mainly studied. Phase composition and morphology of Ti foil substrates and ZnO films were characterized with XRD, SEM and TEM. J-V curves of the FDSSCs were tested by solar simulator and Keithley 2400. Electrochemical impedance spectroscopy (EIS) was also carried out to analyze the internal electronic transmission. The results show that when the Ti foil substrates were treated by using acid polishing, and the ZnO nanosheets were modified for 5 h by immersing in 0.15 mol/L methanol solution of zinc acetate after preheat treatment for 24 h, the FDSSCs displayed optimum performance. Its short circuit current density, open circuit voltage, fill factor and photoelectric conversion efficiency were 11.26 mA/cm2, 0.67 V, 0.60 and 4.51%, respectively.
TiO2 is frequently used as electron transport layer in perovskite solar cells, and its structure can directly affect the performance of MAPbBr3 solar cells. It is necessary to investigate the structural effect of TiO2 to further understand the working mechanism of such kind solar cells. TiO2 thin films with different morphology were prepared by spin coating, and MAPbBr3 (MA = CH3NH3) thin films were further deposited on it through anti-solvent assisted crystallization approach. Then, energy band alignment between TiO2 and MAPbBr3 were characterized by X-ray photoelectron spectroscopy (XPS). According to the experimental results, TiO2 with different morphology possessed different electronic structures and yield different band alignment after contacting with MAPbBr3 perovskite layer. The difference of conduction band value between TiO2 and MAPbBr3 can directly affect the transport and collection feature of electrons, thereby governing the performance of the photovoltaic device.
