Al‐density variation as one driving force for void formation in PERC solar cells

The reduction of void formation in local Al contact structures is of high interest in studies dealing with passivated emitter and rear contact (PERC) solar cells. So far, several processing parameters and their impact on local contact formation were investigated in detail. However, up to now density variation of Al in dependence on temperature and Si content in the melt were not taken into account as a principal reason for void formation. In this context the current assumption of a constant volume of the Al paste particles is discussed in more detail. Based on the results of energy dispersive X‐ray spectroscopy, void formation implies either an expansion of paste particles or their burst during contact formation.

     

Light‐induced degradation and regeneration of multicrystalline silicon Al‐BSF and PERC solar cells

Light‐induced degradation (LID) is a well‐known problem faced by p‐type Czochralski (Cz) monocrystalline silicon (mono‐Si) wafer solar cells. In mono‐Si material, the physical mechanism has been traced to the formation of recombination active boron‐oxygen (B–O) complexes, which can be permanently deactivated through a regeneration process. In recent years, LID has also been identified to be a significant problem for multicrystalline silicon (multi‐Si) wafer solar cells, but the exact physical mechanism is still unknown. In this work, we study the effect of LID in two different solar cell structures, aluminium back‐surface‐field (Al‐BSF) and aluminium local back‐surface‐field (Al‐LBSF or PERC (passivated emitter and rear cell)) multi‐Si solar cells. The large‐area (156 mm × 156 mm) multi‐Si solar cells are light soaked under constant 1‐sun illumination at elevated temperatures of 90 °C. Our study shows that, in general, PERC multi‐Si solar cells degrade faster and to a greater extent than Al‐BSF multi‐Si solar cells. The total degradation and regeneration can occur within ～320 hours for PERC cells and within ～200 hours for Al‐BSF cells, which is much faster than the timescales previously reported for PERC cells. An important finding of this work is that Al‐BSF solar cells can also achieve almost complete regeneration, which has not been reported before. The maximum degradation in Al‐BSF cells is shown to reduce from 2% (relative) to an average of 1.5% (relative) with heavier phosphorus diffusion.     

Emitter of hetero-junction solar cells created using pulsed rapid thermal annealing

In this paper, we use a pulsed rapid thermal processing (RTP) approach to create an emitter layer of hetero-junction solar cell. The process parameters and crystallization behaviour are studied. The structural, optical and electric properties of the crystallized films are also investigated. Both the depth of PN junction and the conductivity of the emitter layer increase with the number of RTP pulses increasing. Simulation results show that efficiencies of such solar cells can exceed 15% with a lower interface recombination rate, but the highest efficiency is 11.65% in our experiments.     

Light‐induced degradation of PECVD aluminium oxide passivated silicon solar cells

Light‐induced degradation (LID) has been identified to be a critical issue for solar cells processed on boron‐doped silicon substrates. Typically, Czochralski‐grown silicon (Cz‐Si) has been reported to suffer from stronger LID than block‐cast multicrystalline silicon (mc‐Si) due to higher oxygen concentrations. This work investigates LID under conditions practically relevant under module operation on different cell types. It is shown that aluminium oxide (AlOx) passivated mc‐Si solar cells degrade more than a reference aluminium back surface field mc‐Si cell and, remarkably, an AlOx passivated Cz‐Si solar cell. The defect which is activated by illumination is shown to be doubtful a sole bulk effect while the AlOx passivation might play a certain role. This work may contribute to a re‐evaluation of the suitability of boron‐doped Cz‐ and mc‐Si for solar cells with very high efficiencies. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Investigation on antireflection coatings for Al:ZnO in silicon thin-film solar cells

We numerically investigate the role of antireflection (AR) coatings, composed of SiO₂ and/or ZnO, in suppression of interfacial reflections in the presence of the transparent conducting oxide, Al-doped ZnO (AZO). Three structures are simulated: (a) AR coatings in organic light-emitting diodes (OLEDs) and flat panel displays, (b) AR coating located between the glass and the AZO, and (c) same as the case b except the involvement of another AR coating between the AZO and the amorphous silicon layers. The weighted average transmittance according to the AM1.5 solar spectrum, the photovoltaic transmittance (T_pv), suggests that there is no evident difference between the structures a and b, especially when the layer number of AR coatings is less than three. An effective way to improve T_pv is presented in the structure c, where T_pv is increased from 73.54% to 76.32% with a three-layered AR coating located between AZO and a-Si. It implies that the suppression of interfacial reflections, resulting from the considerable mismatch of refractive indices at the interface of AZO and a-Si, would benefit the efficiency improvement of silicon thin-film solar cells.     

Reduction of the phosphorus contamination for plasma deposition of p-i-n microcrystalline silicon solar cells in a single chamber

This paper investigates several pretreatment techniques used to reduce the phosphorus contamination between solar cells. They include hydrogen plasma pretreatment, deposition of a p-type doped layer, i-a-Si:H or μc-Si:H covering layer between solar cells. Their effectiveness for the pretreatment is evaluated by means of phosphorus concentration in films, the dark conductivity of p-layer properties and cell performance.     

Analysis and simulation of incident photon to current efficiency in dye sensitized solar cells

Conversion of solar energy into electricity is a challenging issue of today’s renewable energy. Electrochemical dye solar cells (DSC), based on nanostructured TiO₂ particles are a very promising class of photovoltaic devices [6]. The mechanism beyond the conversion of the light is quite different from any other solid state solar cell, resulting from the interplay of a fine tuning of the energy levels of the cell components and a delicate fabrication process. This complexity needs a reliable transport model, able to catch the device as a whole and applicable to experimental set up. We developed an extension of TiberCAD [7] code to simulate such kind of devices and compared the calculation with incident photon to current efficiency (IPCE) measurements.     

多温度阶梯退火对有机聚合物太阳能电池器件性能的影响

以聚3-己氧基噻吩(P3HT)作为给体,富勒烯衍生物(ICBA)作为受体,制备了体异质结结构的聚合物太阳能电池,研究不同热退火条件对器件的光伏输出特性及稳定性的影响.研究发现,采用多温度、阶梯退火比单一温度退火能使器件的光伏输出性能明显提高,与此同时器件的寿命显著延长,可以在未封装的环境下保持器件性能的稳定,减缓器件的衰退.     

Co‐diffusion from solid sources for bifacial n‐type solar cells

We present a simplified process sequence for the fabrication of large area n‐type silicon solar cells. The boron emitter and full area phosphorus back surface field are formed in one single high temperature step using doped glasses deposited by plasma enhanced chemical vapour deposition (PECVD) as diffusion sources. By optimizing the gas composition during the PECVD process, we not only prevent the formation of a boron rich layer (BRL), but also achieve doping profiles that exhibit a low dark saturation current density while allowing for contact formation by screen printing. The presented co‐diffusion process allows for major process simplification compared to the state of the art diffusion process relying on multiple high temperature processes, masking and wet chemistry steps.

     

Comparison of D.C. and A.C. electro-analytical methods for measuring diode ideality factors and series resistances of silicon solar cells

The diode ideality factor (m) and the series resistance (R_s) of a Si solar cell represent two critical performance-indicator parameters of the device. Since both m and R_s are functions of voltage (V) and temperature (T), simultaneous electrical measurements of these parameters under variable conditions of V and T can often be difficult with traditional direct current (D.C.) techniques. Using the electro-analytical method of linear sweep voltammetry (LSV) and a commonly available Si solar cell, we explore these specific confines of such D.C. measurements. The results are compared with those obtained from a parallel set of alternating current (A.C.) measurements using impedance spectroscopy (IS). LSV provides the main D.C. parameters (open circuit voltage, short circuit current, fill factor, and efficiency) of the cell, but is limited in terms of independently measuring m and R_s beyond strong forward biased conditions. The IS approach is free of the latter experimental constraints, and at the same time can provide several other important electrical parameters of the solar cell. Specifically, IS detects the presence of a low-high (p–p⁺) junction at the back surface of the cell, and serves as an efficient probe of certain electrical characteristics of this junction.     

Effect of rapid thermal oxidation on structure and photoelectronic properties of silicon oxide in monocrystalline silicon solar cells

This paper concerns the topic of surface passivation properties of rapid thermal oxidation on p-type monocrystalline silicon wafer for use in screen-printed silicon solar cells. It shows that inline thermal oxidation is a very promising alternative to the use of conventional batch type quartz tube furnaces for the surface passivation of industrial phosphorus-diffused emitters. Five minutes was the most favorable holding time for the rapid thermal oxidation growth of the solar cell sample, in which the average carrier lifetime was increased 19.4 μs. The Fourier transform infrared spectrum of the rapid thermal oxidation sample, whose structure was Al/Al-BSF/p-type Si/n-type SiP/SiO₂/SiN_x/Ag solar cell with an active area of 15.6 cm², contained an absorption peak at 1085 cm⁻¹, which was associated with the Si–O bonds in silicon oxide. The lowest average reflectance of this sample is 0.87%. Furthermore, for this sample, its average of internal quantum efficiency and conversion efficiency are respectively increased by 8% and 0.23%, compared with the sample without rapid thermal oxidation processing.     

Laser illumination for manipulation of hydrogen charge states in silicon solar cells

This Letter investigates the important parameters of illumination for control of hydrogen charge states in p‐type silicon solar cells. Through variations in the wavelength and intensity of illumination, evidence is provided for the importance of the neutral charge state of interstitial hydrogen, H⁰, for the passivation of defects in upgraded metallurgical grade (UMG) silicon. It is shown that through this approach minority carrier lifetimes may be achieved in excess of those realised through previous techniques, resulting in open‐circuit voltages (iV_OC) over 710 mV. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Advantages of InGaN/GaN multiple quantum well solar cells with stepped-thickness quantum wells

InGaN/GaN multiple quantum well (MQW) solar cells with stepped-thickness quantum wells (SQW) are designed and grown by metal-organic chemical vapor deposition. The stepped-thickness quantum wells structure, in which the well thickness becomes smaller and smaller along the growth direction, reveals better crystalline quality and better spectral overlap with the solar spectrum. Consequently, the short-circuit current density (Jsc) and conversion efficiency of the solar cell are enhanced by 27.12% and 56.41% compared with the conventional structure under illumination of AM1.5G (100 mW/cm2). In addition, approaches to further promote the performance of InGaN/GaN multiple quantum well solar cells are discussed and presented.     

新型空间硅太阳电池纳米减反射膜系的优化设计

结合纳米材料折射率（小于1.4）和AM0太阳光谱特性,对空间硅太阳电池的减反射膜进行了设计分析.分别设计了常规材料和纳米材料的双层、三层减反射膜,得到了最佳的膜系参数,并作出了反射率变化曲线.结果发现,采用低折射率纳米材料的三层减反射膜有着更好的减反射效果,新型纳米减反射膜系与采用常规材料的减反射膜系相比,优化后的最小加权平均反射率减小了15%（双层减反射膜）和24.5%（三层减反射膜）. 关键词： 折射率 减反射膜 纳米材料 空间硅太阳电池     

Effect on the reduction of the barrier height in rear-emitter silicon heterojunction solar cells using Ar plasma-treated ITO film

In this study, we investigated the effect of plasma treatment on an indium tin oxide (ITO) film under an ambient Ar atmosphere. The sheet resistance of the plasma-treated ITO film at 250 W (37.6 Ω/sq) was higher than that of the as-deposited ITO film (34 Ω/sq). Plasma treatment was found to decrease the ITO grain size to 21.81 nm, in comparison with the as-deposited ITO (25.49 nm), which resulted in a decrease in the Hall mobility. The work function of the Ar-plasma-treated ITO (WF_ITO=4.17 eV) was lower than that of the as-deposited ITO film (WF_ITO = 5.13 eV). This lower work function was attributed to vacancies that formed in the indium and oxygen vacancies in the bonding structure. Rear-emitter silicon heterojunction (SHJ) solar cells fabricated using the plasma-treated ITO film exhibited an open circuit voltage (V_OC) of 734 mV, compared to SHJ cells fabricated using the as-deposited ITO film, which showed a V_OC of 704 mV. The increase in V_OC could be explained by the decrease in the work function, which is related to the reduction in the barrier height between the ITO and a-Si:H (n) of the rear-emitter SHJ solar cells. Furthermore, the performance of the plasma-treated ITO film was verified, with the front surface field layers, using an AFORS-HET simulation. The current density (J_SC) and V_OC increased to 39.44 mA/cm² and 736.8 mV, respectively, while maintaining a WF_ITO of 3.8 eV. Meanwhile, the efficiency was 22.9% at V_OC = 721.5 mV and J_SC = 38.55 mA/cm² for WF_ITO = 4.4 eV. However, an overall enhancement of 23.75% in the cell efficiency was achieved owing to the low work function value of the ITO film. Ar plasma treatment can be used in transparent conducting oxide applications to improve cell efficiency by controlling the barrier height.     

有机共混结构叠层太阳电池的研究进展

有机太阳电池由于质轻、价廉、柔性,受到人们的广泛关注.单个有机材料只能吸收部分太阳光,叠层结构的太阳电池将不同吸收带隙的有机材料通过中间层连接起来,既能充分吸收太阳光,又能提高太阳电池的开路电压或短路电流.本文综述了近年来有机共混结构叠层太阳电池的研究进展,介绍了各种叠层有机太阳电池的结构、原理及性能,阐述了国内外有机叠层太阳电池研究的现状及存在问题,为高性能有机太阳电池的研究提供有价值的参考.     

Design of perylene-diimides-based small-molecules semiconductors for organic solar cells

A series of perylene-diimide-based small molecules have been designed to explore their optical, electronic and charge transport properties as organic solar cell materials. The frontier molecular orbitals analysis has turned out that the vertical electronic transitions of absorption are characterised as intramolecular charge transfer between perylene diimide moieties and substituent aromatic groups. Our results suggest that the optical and electronic properties and reorganisation energies are affected by the introduction of different aromatic groups to these molecules. The calculation results showed that the designed molecules own the large longest wavelength of absorption spectrum, the oscillator strength and absorption region values. On the basis of the investigated results, the designed molecules could be used as solar cell material with intense broad absorption spectra. Furthermore, they are expected to be the promising candidates for hole and/or electron transport materials.     

Applications and functions of rare-earth ions in perovskite solar cells

The emerging perovskite solar cells have been recognized as one of the most promising new-generation photovoltaic technologies owing to their potential of high efficiency and low production cost. However, the current perovskite solar cells suffer from some obstacles such as non-radiative charge recombination, mismatched absorption, light induced degradation for the further improvement of the power conversion efficiency and operational stability towards practical application. The rare-earth elements have been recently employed to effectively overcome these drawbacks according to their unique photophysical properties. Herein, the recent progress of the application of rare-earth ions and their functions in perovskite solar cells were systematically reviewed. As it was revealed that the rare-earth ions can be coupled with both charge transport metal oxides and photosensitive perovskites to regulate the thin film formation, and the rare-earth ions are embedded either substitutionally into the crystal lattices to adjust the optoelectronic properties and phase structure, or interstitially at grain boundaries and surface for effective defect passivation. In addition, the reversible oxidation and reduction potential of rare-earth ions can prevent the reduction and oxidation of the targeted materials. Moreover, owing to the presence of numerous energetic transition orbits, the rare-earth elements can convert low-energy infrared photons or high-energy ultraviolet photons into perovskite responsive visible light, to extend spectral response range and avoid high-energy light damage. Therefore, the incorporation of rare-earth elements into the perovskite solar cells have demonstrated promising potentials to simultaneously boost the device efficiency and stability.     

Nanoroughness control of Al-Doped ZnO for high efficiency Si thin-film solar cells

The Al-doped ZnO (ZnO:Al) front transparent conducting oxide (TCO) for high efficiency Si thin-film solar cell has been developed using RF magnetron sputtering deposition and chemical wet etching. Microscopic surface roughness of the as-deposited ZnO:Al film estimated by spectroscopic ellipsometry is closely related to the compactness of the TCO film, and shown to be a straightforward and powerful tool to optimize the deposition conditions for the proper post-etched surface morphology. Wet-etching time is adjusted to form the U-shaped craters on the surface of the ZnO:Al film without sharp etch pits that can cause the crack-like defects in the overgrown microcrystalline Si-absorbing layers, and deteriorate the V_oc and FF of the Si thin-film solar cells. That is to say, the nanoroughness control of the as-deposited TCO film with proper chemical etching is the key optimization factor for the efficiency of the solar cell. The a-Si:H/a-SiGe:H/μc-Si:H triple junction Si thin-film solar cells grown on the optimized ZnO:Al front TCO with anti-reflection coatings show higher than 14% conversion efficiency.     

Ultrasonic irradiation preparation of graphitic-C3N4/polyaniline nanocomposites as counter electrodes for dye-sensitized solar cells

In this research, polyaniline/graphitic carbon nitride (PANI/g-C₃N₄) nanocomposites were synthesized via in-situ electrochemical polymerization of aniline monomer whit different number of cyclic voltammetry scans (10, 20 and 30 cycles) after electrode surface pre-preparation using a potential shock under ultrasonic irradiation. PANI/g-C₃N₄ nanocomposites with two values of g-C₃N₄ (0.010 wt% and 0.015 wt%) were deposited on the surface of the transparent conducting film (FTO glass) by immersing FTO into the aniline solution and g-C₃N₄ during the electro-polymerization. The resulting PANI/g-C₃N₄ films were characterized by Fourier transformed infra-red (FTIR), power X-ray diffraction (PXRD), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) techniques. The prepared electrodes were applied as counter electrode in dye-sensitized solar cells. Among them, the prepared electrode with 10 cycles and 0.01 wt% g-C₃N₄ showed the best efficiency. These hybrids show good catalytic activity in elevating tri-iodide reduction and due to the synergistic effect of PANI and g-C₃N₄, PANI/g-C₃N₄ nanocomposite electrode shows power conversion efficiency about 1.8%.