Solar Cell Processing Research Articles

Morphology evolution of the light trapping structure using atmospheric plasma textured c-Si wafer for silicon solar cells

Applying atmospheric plasma etching to the surface texturing process of silicon solar cells is a promising strategy for the current photovoltaic manufacturing industry due to its low equipment cost and good fabrication flexibility. This paper investigates the morphology evolution of the silicon surface etched by an Ar/CF4/O2 plasma and the associated optical properties. Results show that the generation of the light trapping structure on the polished silicon surface can be divided into two stages on the basis of the multi-scale morphological images and the quantitative evaluation of roughness parameters. The initial roughening stage mainly involves the formation of high-frequency nanoroughness that can act as an effective medium layer with a gradual refractive index. The resulting optical medium effect can reduce the surface reflectance within a broad range of wavelengths. At the next texturing stage, the low-frequency and high-amplitude microroughness dominates the morphology of the etched silicon surface. It features inverted parabolic structures with a high aspect ratio, which can cause multiple reflections of the incident light. The optical medium effect resulting from the nanoroughness is also inherited. Thus, the anti-reflectance property of the etched silicon surface is greatly improved. This work demonstrates that the light trapping properties of silicon surface etched by atmospheric plasma jet are a synergy of the optical medium effect and geometrical optics. Insights into the morphology evolution and optical properties of the textured surfaces are important for developing a new surface texturing process of silicon solar cells.

Plasma etching: a strategy to enhance the photovoltaic conversion efficiency of ultrathin CdTe solar cells

Ultrathin CdTe solar cell is a promising application of using integrated photovoltaics to act as architectural components and bifacial devices to promote the utilization of sunlight. In the preparation process of the ultrathin CdTe solar cells, the chemical solution etching process before back contact deposition has to be refrained due to the high risk of shunting. Therefore, an alternative strategy to get a clean CdTe surface is required. In this work, plasma etching treatment was conducted on sputtered ultrathin CdTe films to eliminate the residual oxides induced by CdCl2 treatment. Furthermore, ultrathin bifacial CdTe solar cells with a structure of glass/FTO/SnO2/CdS/CdTe (∼920 nm)/CuCl/ITO were fabricated to investigate the effect of plasma etching on the device performance. As a result, by employing plasma etching treatment, a bifacial device with a front illuminated efficiency of up to 9.93% and a rear illuminated efficiency of 2.41% was achieved. This work provides important indications for the performance optimization of ultrathin CdTe solar cells.

(Invited) Toward a Molecular Understanding of Photoinduced Charge Separation Process in Organic Solar Cells with Computational Approaches

Photoinduced charge separation (CS) process plays important roles in various fields such as natural and artificial photosynthesis, solar cell, and light-emitting diode. To investigate the photoinduced CS process theoretically, the CS state is often regarded as “static exciton” and described by several parameters such as free energy difference and electronic coupling between initial and final states according to Marcus theory. However, dynamical effects such as nuclear motions and spin-orbit coupling (SOC) are recently being recognized as important factors for controlling the CS efficiency. Therefore, the CS state should be considered as “dynamic exciton.” To analyze the dynamic exciton theoretically, we need to treat the photoexcited reaction dynamics quantum mechanically, where the locally excited and CS states, electronic coupling and SOC dynamically fluctuates. In addition, surrounding environment such as solvent are also important and required to be explicitly considered because the charge distribution of CS state is much different from that of initial state. It is impossible to treat all the systems including surroundings quantum mechanically. Therefore, combined quantum mechanical and molecular mechanical (QM/MM) method, in which an important subsystem is described quantum mechanically whereas the other surrounding is treated by molecular mechanics force field, is an essential tool. However, even the QM/MM method still requires large computational cost for the analysis of dynamic exciton because the calculation time of excited state is much longer than that of ground state. To overcome this difficulty, we have been developing several methods combining the QM/MM method and molecular dynamics simulation efficiently. In this presentation, we will show several applications toward a molecular understanding of photoinduced CS process in organic solar cells.

Elucidating the Trajectory of the Charge Transfer Mechanism and Recombination Process of Hybrid Perovskite Solar Cells.

Perovskite-based solar cells (PSCs) have attracted attraction in the photovoltaic community since their inception in 2009. To optimize the performance of hybrid perovskite cells, a primary and crucial strategy is to unravel the dominant charge transport mechanisms and interfacial properties of the contact materials. This study focused on the charge transfer process and interfacial recombination within the n–i–p architecture of solar cell devices. The motivation for this paper was to investigate the impacts of recombination mechanisms that exist within the interface in order to quantify their effects on the cell performance and stability. To achieve our objectives, we firstly provided a rationale for the photoluminescence and UV-Vis measurements on perovskite thin film to allow for disentangling of different recombination pathways. Secondly, we used the ideality factor and impedance spectroscopy measurements to investigate the recombination mechanisms in the device. Our findings suggest that charge loss in PSCs is dependent mainly on the configuration of the cells and layer morphology, and hardly on the material preparation of the perovskite itself. This was deduced from individual analyses of the perovskite film and device, which suggest that major recombination most likely occur at the interface.

Adapting M2 silicon half-wafers processing on industrial-scale equipment dedicated to 4″ solar technology

PurposeThe purpose of this study is to address the issue of technology equipment formerly dedicated to the process of 4- and even 5-inch photovoltaic cells and whose use has become critical with the evolution of silicon wafer size standards (M2–M10). Fortunately, the recent concept of 6'' half-cut cell with its many advantages appears promising insofar as it offers the possibility of further extend the use of costly, still operational process equipment, but doomed to obsolescence.Design/methodology/approachIn the background of a detailed Al-BSF process, the authors show how to experimentally adapt specific accessories and arrange 6” half-wafers to enable the upgrade of a complete industrial process of silicon solar cells at a lower cost. Step by step, the implementation of the processes for the two wafer sizes (4” wafers and 6” half wafers) is compared and analyzed in terms of performance and throughput.FindingsGlobally, the same process effectiveness is observed for both types of wafers with slightly better sheet resistance uniformity for the thermal diffusion carried out on the half wafers; however, the horizontal arrangement of the wafer carriers in the diffusion and the plasma-enhanced chemical vapor deposition tubes limits the thermal balance regarding the total number of cells processed per batch.Originality/valueIn terms of the development of prototypes on a preindustrial scale, this paves the way to further continue operating outdated equipment for high-performance processes (passivated emitter and rear contact, Tunnel oxide passivated contact (TOPCon)), while complying with current standards for silicon wafers up to M10 format.

Influence of spin-coating methods on the properties of planar solar cells based on ambient-air-processed triple-cation mixed-halide perovskites

Highly efficient perovskite solar cells based on triple-cation mixed-halide perovskite (CsFAMAPbIBr) require a strictly controlled environment such as a N2-filled glove box and/or a dry room due to the instability of formamidinium (FA) ions in humid environment. Furthermore, sufficient knowledge regarding the detailed ambient air processing techniques is lacking. Therefore, the processing of efficient CsFAMAPbIBr-based solar cells in ambient air atmosphere is very challenging and essential for low-cost commercialization. Herein, the effect of different coating methods, static spin coating and dynamic spin coating, on the fabrication of two-step ambient-air-processed CsFAMAPbIBr films and the photovoltaic properties of CsFAMAPbIBr-based planar solar cells is presented. Different compositions and morphologies of CsFAMAPbIBr are obtained because of the different reaction times between the pre-deposited PbI2-CsI layer and the secondary deposited organic materials (FAI/MABr/MACl) in static and dynamic spin-coating methods, which lead to differences in Ostwald ripening and ion exchange in ambient-air atmosphere, thereby substantially affecting the power conversion efficiency (PCE) and stability of the fabricated solar cells. Planar solar cells based on dynamic-spin-coated CsFAMAPbIBr exhibit a higher PCE of 19.70% (17.27% ± 1.25%), than those based on static-spin-coated CsFAMAPbIBr, whose PCE was 16.01% (9.89% ± 2.34%).

Individual efficiencies of a polycrystalline silicon PV cell versus temperature

The present paper is about an investigation on the temperature dependence of efficiencies of individual energetic process (Absorption efficiency, Thermalization efficiency, Thermodynamic efficiency and Fill factor) and overall conversion efficiencies of a polycrystalline silicon solar cell which has been investigated in temperature range 10–50 °C. All these individual efficiencies present a decrease versus the increase of the temperature. However, the thermodynamic efficiency and the fill factor are more sensitive to the temperature increase more than the absorption and thermalization efficiencies. The thermodynamic efficiency and the fill factor degradation is explained by decrease of open circuit voltage in temperature. The performance parameters as open circuit voltage, maximum power and the overall efficiencies are found to decrease with temperature while the short circuit current is observed an increase. The resistance of the semiconductor decreases with the increase of the temperature. The minoritary carriers charge acquire excessive kinetic energy which can exceed the gap energy causing an over-excitement when the temperature increase. However, this over-excitement of the minoritary carriers charge does not participate to the external current improvement.

Room-temperature carbon electrodes with ethanol solvent interlacing process for efficient and stable planar hybrid perovskite solar cells

Among the next-generation photovoltaic technologies, perovskite solar cells (PSCs) have attracted significant attention and interest. However, PSCs typically use high-vacuum processed metal electrodes, which are considerably more expensive. Furthermore, this process using noble metals, results in dramatic performance degradation after halide ion migration and thermal stress. Therefore, replacing metal electrodes with carbon electrodes is a promising way to address the stability issues of PSCs. This is due to carbon materials possessing unique qualities, such as low cost, high stability, good conductivity, and inherent water resistance. In contrast, some solvents in commercial carbon paste cause damage to the structure of perovskite films. Herein, room-temperature carbon films were successfully prepared utilizing an ethanol solvent interlacing process with time optimization. The resulting carbon films exhibited good flexibility inducing tight adhesion onto the hole transporting layer as well as excellent electrical properties. The carbon films were then applied as working electrodes in PSCs structured as FTO/TiO2/Cs0.17FA0.83Pb(I0.83Br0.17)3/spiro-OMeTAD/carbon. By optimizing time, in the ethanol solvent interlacing process, an excellent power conversion efficiency (PCE) was achieved. The devices improved up to 12.2% using the soaked carbon films at 2 h. Moreover, the device exhibits excellent long-term stability of 80% over 1000 h in air environment without encapsulation. Finally, this simple and effective technique proposes an alternate choice for developing efficient carbon-based PSCs.

ИЗУЧЕНИЕ ВЛИЯНИЯ ТЕМПЕРАТУРЫ НА ФОТОЭЛЕКТРИЧЕСКИЕ ПРОЦЕССЫ В КРЕМНИЕВЫХ СОЛНЕЧНЫХ ЭЛЕМЕНТАХ С ПОМОЩЬЮ ЦИФРОВОГО МОДЕЛИРОВАНИЯ

the method of digital modelling investigates influence of temperature on photo- electric processes in silicon solar cells. Feat ure of program system “Sentaurus TCAD” which allowed to model silicon solar cells with flat p- n-junction is described. Are calculated of the I-V characteristic of the solar cells containing platin um nanoparticles and without them at a variation of temperature in a range 250÷350 K. Sizes of the basic photo -electric parameters of solar cells for various values of temperature are defined

Advanced selection materials in solar cell efficiency and their properties - A comprehensive review

Solar cell layers technology has achieved global standing in the solar cell layers deposition process, and it covers the innovative methods and techniques in significant applications. Recent solar cell layers technology has an advanced interest in a refined approach to enhance performance and highlights the importance of recent proficient procedures for manufacturing. For example, the application is used to search for novel materials for solar cells' layers to clarify the current energy crisis. The technological process and various types of solar cells depend on climate change. Among them, layers of solar cells and silicon wafer solar cells are very encouraging. Solar cell layers technology has led to solar cells being a more reasonable active option in design and production. The productivities facilitated by new solar cells still need to be enhanced for the various processes involved in the additional enhancement from Copper Indium Gallium Selenide (CIGS) microfilms to solar cell crystal structure dye-sensitized solar cells. The hydrophobic coating works as an anti-dust coating, enhancing efficiency and decreasing the cost of cleaning solar cells. In Saudi Arabia Majmaah City, most solar projects are in dry regions, where the dusty weather reduces solar cell efficiency. Therefore, combining these two properties and applying an anti-reflective and superhydrophobic coating will increase solar cell efficiency by 20%. Solar cells' crystal structure results are substituted with layers or new materials to balance environmental impact and toxic nature.

Solution processing of polymer solar cells: towards continuous vacuum-free production

Roll-to-roll (R2R) production is essential for commercial mass production of organic photovoltaics, avoiding energy costs related to the inert atmosphere or vacuum steps. This work provides a complete review of various techniques and materials that have been used for the R2R production of bulk heterojunction polymer solar cells. Various fabrication parameters have been identified and discussed to improve the mass production process, aiming to obtain better-performing devices. The evolution of PCE and FF values of all-solution and partially R2R-processed modules over the last decade has been established, verifying the continuous evolution in this field. The life cycle analyses have confirmed that industrially processed modules through R2R processes have great potential to realize industrial production of high-performance R2R solar cell devices with an immediate goal of 10% PCE, 10 years durability, and less CO2 emissions with consequent lower energy payback time than other solar technologies. Currently, several laboratories have reported PCE values over 10% for small-area active layers fabricated by R2R techniques. However, the fabrication of large-area modules remains challenging. At the end of this document, based on the collected results, we propose a sequence of R2R compatible processes for an all-solution ITO-free solar device with high performance.

Lead-free tin perovskite solar cells

Summary The development of efficient and stable lead-free perovskite solar cells (PSCs) is crucial for addressing the concern of environmental pollution from the toxic element lead. In recent years, tin PSCs have emerged as a promising candidate for high-performance, eco-friendly photovoltaic technology with a high certified power conversion efficiency (PCE) of more than 11%, indicating a great potential for future applications. Here, we review the recent efficiency progress of tin PSCs based on the equivalent circuit model of solar cells. We then discuss approaches toward efficiency improvement from the device viewpoint, such as optimizing the band gap, increasing the light-harvesting efficiency and carrier diffusion length, surface passivation, and regulating the interface energy-level alignment. Finally, we point out the possibility of reaching 20% PCE for tin PSCs and issues regarding enlarging the cell size and realizing scalable production in the future. We expect that these perspectives will be helpful for accelerating the commercialization of tin PSCs.

Downshifting and Antireflective Thin Films for Solar Module Power Enhancement

Efforts to enhance the solar conversion efficiency have prevailed for decades. There is a growing interest in improving the spectral response of solar modules, especially in harvesting UV photons, which offer intense energy in a narrow wavelength range. To harvest UV photons and reduce reflection without interfering with the formulas and manufacturing process of solar cells, in this work, thin films that possess downshifting and antireflection capabilities were fabricated on the cover glass of multicrystalline Si solar cells. The thin films were composed of graded index layers of europium-doped yttrium orthovanadate (YVO4:Eu) and hollow silica nanoparticles (HSNPs). The design of the composite thin films was assisted by the FDTD mathematical model that simulated the refractive index and thickness of each layer to obtain the optimum transmittance. The cover glass with multifunctional thin films harvested more than 30 % of UV photons and enhanced the solar conversion efficiency by 4.12 % at normal incidence compared to the uncoated cover glass.

Study on loss processes in solar cells

Determining heat sources for solar cells is essential to avoid energy loss, which in turn causes the efficiency of solar cells to decrease and therefore, the loss processes have a significant impact on solar conversion. This paper presents a study of intrinsic and exogenous losses in solar cells, identification of the resulting energy loss at different temperatures, and discusses the impact of exogenous and spectral reflectivity on solar cell performance. The results show an increase in thermal loss with an increase in temperature, which in turn leads to a decrease in the efficiency of solar cells. Also explained that the external radiate efficiency, spectral reflectance and operating temperature significantly affect the loss processes. The efficiency of the cell begins to decrease with the decrease of its external radiate efficiency.

Coarse-Grained Quantum Theory of Organic Photovoltaic Devices.

Understanding the exciton dissociation process in organic solar cells is a fundamental issue for the design of high-performance photovoltaic devices. In this article, a parameterized quantum theory based on a coarse-grained tight-binding model plus non-local electron-hole interactions is presented, while the diffusion and recombination of excitons are studied in a square lattice of excitonic states, where a real-space renormalization method on effective chains has been used. The Hamiltonian parameters are determined by fitting the measured quantum efficiency spectra and the theoretical short-circuit currents without adjustable parameters show a good agreement with the experimental ones obtained from several polymer:fullerene and polymer:polymer heterojunctions. Moreover, the present study reveals the degree of polymerization and the true driving force at donor-acceptor interface in each analyzed organic photovoltaic device.

Dry Phosphorus silicate glass etching and surface conditioning and cleaning for multi-crystalline silicon solar cell processing

As an alternative to the wet chemical etching method, dry chemical etching processes for Phosphorus silicate glass [PSG} layer rel11ova] using Tri?uormethane/Sulfur Hexafluoride (CHF3/ SF6) gas mixture in commercial silicon-nitride plasma enhanced chemical vapour deposition (SiN-PECVD) system is applied. The dependence of the solar cell performance on the etching temperature is investigated and optimized. It is found that the SiN-PECVD system temperature variation has a signi?cant impact on the whole solar cell characteristics. A dry plasma cleaning treatment of the Si wafer surface after the PSG removal step is also investigated and developed. The cleaning step is used to remove the polymer ?lm which is formed during the PSG etching using both oxygen and hydrogen gases. By applying an additional cleaning step, the polymer ?lm deposited on the silicon wafer surface after PSG etching is eliminated. The effect of different plasma cleaning conditions on solar cell performance is investigated. After optimization of the plasma operating conditions, the performance of the solar cell is improved and the overall gain in ef?ciency of 0.6 % absolute is yielded compared to a cell without any further cleaning step. On the other hand, the best solar cell characteristics can reach values close to that achieved by the conventional wet chemical etching processes demonstrating the effectiveness of the additional O2/H2 post cleaning treatment.

Molecular design revitalizes the low-cost PTV-polymer for highly efficient organic solar cells.

Developing photovoltaic materials with simple chemical structures and easy synthesis still remains a major challenge in the industrialization process of organic solar cells (OSCs). Herein, an ester substituted poly(thiophene vinylene) derivative, PTVT-T, was designed and synthesized in very few steps by adopting commercially available raw materials. The ester groups on the thiophene units enable PTVT-T to have a planar and stable conformation. Moreover, PTVT-T presents a wide absorption band and strong aggregation effect in solution, which are the key characteristics needed to realize high performance in non-fullerene-acceptor (NFA)-based OSCs. We then prepared OSCs by blending PTVT-T with three representative fullerene- and NF-based acceptors, PC71BM, IT-4F and BTP-eC9. It was found that PTVT-T can work well with all the acceptors, showing great potential to match new emerging NFAs. Particularly, a remarkable power conversion efficiency of 16.20% is achieved in a PTVT-T:BTP-eC9-based device, which is the highest value among the counterparts based on PTV derivatives. This work demonstrates that PTVT-T shows great potential for the future commercialization of OSCs.

Inverted planer perovskite solar cells fabricated by all vapor phase process

A simple vapor-based fabrication process for perovskite solar cells is developed and applied to the fabrication of inverted planar CH3NH3PbI3 (MAPbI3) perovskite solar cells. In this process, PbI2 film is deposited by vacuum evaporation on the hole transport layer (HTL), followed by converting it into the MAPbI3 phase by annealing in methylammonium iodide (MAI) vapor. Using the converted MAPbI3 films, we fabricated inverted planar perovskite solar cells by vapor phase-based process with a device structure of glass/TCO/HTL/MAPbI3/C60/BCP/Ag, in which PEDOT:PSS and copper phthalocyanine (CuPc) were used as an HTL. A power conversion efficiency as high as 16.1% was obtained for the solar cell using CuPc as an HTL by a fully vapor-based process. Furthermore, we observed the improvement of the stability of the solar cells when using CuPc instead of PEDOT:PSS as an HTL.

Vacuum deposited PbI2 film grown at elevated temperatures for improved efficiency of CH3NH3PbI3 based planar perovskite solar cells

Herein, we report on the elevated temperature vacuum deposition of PbI2 film and its conversion into high-quality CH3NH3PbI3 perovskite film using a two-step vapor-solution deposition process for perovskite solar cells. The CH3NH3PbI3 perovskite films made with PbI2 layer deposited at elevated temperature possess large grain size and pinhole-free morphology, and they exhibit very high absorption and low radiative recombination. We fabricated FTO/PEDOT:PSS/CH3NH3PbI3/PCBM/Al planar perovskite solar cells using PbI2 layers deposited at different substrate temperatures. Interestingly, we observed a major improvement (∼65 %) in the power conversion efficiency of the cell using the perovskite film grown with PbI2 film deposited at 150 °C as compared to the film grown at room temperature. These devices show enhanced ambient stability compared to the case of the PbI2 layer deposited at room temperature. The origin of highly improved performance and higher stability of the devices made with elevated temperature deposition is investigated in detail.

Identification of the dominant recombination process for perovskite solar cells based on machine learning

Over the past decade, perovskite solar cells have become one of the major research interests of the photovoltaic community, and they are now on the brink of catching up with the classical inorganic solar cells, with efficiency now reaching up to 25%. However, significant improvements are still achievable by reducing recombination losses. The aim of this work is to develop a fast and easy-to-use tool to pinpoint the main losses in perovskite solar cells. We use large-scale drift-diffusion simulations to get a better understanding of the light intensity dependence of the open-circuit voltage and how it correlates to the dominant recombination process. We introduce an automated identification tool using machine learning methods to pinpoint the dominant loss using the light intensity-dependent performances as an input. The machine learning was trained using >2 million simulations and gives an accuracy of the prediction up to 82%.