Solar Cell Processing Research Articles

Investigation of air-stable Cs2SnI6 films prepared by the modified two-step process for lead-free perovskite solar cells

In recent years, the organic-inorganic perovskite materials have revolutionized the Photovoltaic industry with highly efficient power conversion devices accompanied by a high growth rate. However, these devices experience major environmental and stability issues that hinder their true potential. More recently, a rarely studied perovskite material Cs2SnI6 is gaining enormous attention due to its superior stability and suitable bandgap. In this work, we developed a modified two-step process to prepare uniform Cs2SnI6 films, and the influence of the reaction conditions on the properties is explored. The structural, morphological, optical, and electrical properties of the prepared films were investigated using x-ray diffraction, Raman spectroscopy, scanning electron microscopy, UV–vis spectrometer, photoluminescence, and Hall Effect measurements, respectively. Phase stability and morphology of the films are improved with optimizing the reaction conditions. The results confirm the n-type semiconductor nature of Cs2SnI6 with bandgap ranging from 1.29 eV to 1.42 eV with maximum carrier mobility of 425 cm2 V−1 s−1. The present study will further provide potential research directions in improving the device efficiency of air-stable Cs2SnI6 perovskite solar cells.

Performance-Enhancing Approaches for PEDOT:PSS-Si Hybrid Solar Cells.

The emerging energy crisis has focused significant worldwide attention on solar cells. Although crystalline silicon solar cells are currently widely used, their high cost limits the development of solar power generation. Consequently, hybrid solar cells are becoming increasingly important, especially organic-Si hybrid solar cells (HSCs). Organic-Si HSCs combine a mature technology and high efficiency with the low-temperature manufacturing process and tunable optoelectronic properties of organic solar cells. The organic material can be P3HT, carbon nanotubes, graphene, and PEDOT:PSS. Here we review the performance of PEDOT:PSS/Si HSCs and methods for improving their efficiency, such as PEDOT:PSS modification, optimization of the trapping effect, passivation of the silicon surface, addition of an interface layer, improvement of a back contact, and optimization of the metal top electrode. This Review should help fill the gap in this area and provide perspectives for the future development of the PEDOT:PSS/Si HSCs.

Effect of the Heat Treatment on the Microstructure and Morphology of Cigs Thin Films Prepared by RF Magnetron Sputtering at Room Temperature

This work investigates the microstructural and morphological changes on CIGS thin films submitted to a post-deposition heat treatment. The CIGS 1000 nm-thick films were deposited at room temperature by RF magnetron sputtering onto glass substrates covered with molybdenum films. After deposition, the samples were submitted to a heat treatment, with temperatures ranging from 450 to 575 oC. The treatment was also carried out under a selenium atmosphere (selenization), from 400 to 500 oC. Morphological analyzes showed that the as-deposited film was uniform and amorphous. When the treatment was carried out without selenization, the crystallization occurred at or above 450 oC, and the grains remained nanosized. However, high temperatures led to the formation of discontinuities on the film surface and the formation of extra phases, as confirmed by X-ray diffraction data. The crystallization of the films treated under selenium atmosphere took place at lower temperatures. However, above 450 °C the film surface was discontinuous, with a lot of holes, whose amount increased with the temperature, showing that the selenization process was very aggressive. X-ray diffraction analyses showed that the extra phases were eliminated during selenization and the films had a preferential orientation along [112] direction. The results indicate that in the manufacturing process of solar cells, CIGS films deposited at room temperature should be submitted to a heat treatment carried out at 450 °C (without selenization) or 400 °C (with selenization).

A Low-Temperature Solution-Processed CuSCN/Polymer Hole Transporting Layer Enables High Efficiency for Organic Solar Cells.

The hole transporting layers (HTLs) between the electrode and light absorber play a vital role in charge extraction and transport processes in organic solar cells (OSCs). Herein, a bilayer structure HTL of CuSCN/TFB is formed by soluble copper(I) thiocyanate (CuSCN) and poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-(4,4'-(N-(4-butylphenyl)))] (TFB). The excellent charge extraction capability is proved in nonfullerene PM6:Y6 and fullerene PTB7-Th:PC71BM blend system-based cells. The introduction of TFB tunes the work function and polishes the interfacial contact between the HTL and light absorber, which favors the hole extraction process in cells. Meanwhile, lower recombination loss, higher exciton dissociation probability, and larger domain size are observed in CuSCN/TFB HTL-based cells compared to those of the reference cell with the pristine CuSCN HTL, which significantly improve the photovoltaic performance. As a result, a champion efficiency of 15.10% is obtained, which is >14% higher than the efficiency of 13.15% obtained in the reference cell. This study suggests that CuSCN/TFB is a promising HTL to achieve high efficiency for OSCs.

Heteroleptic Tin-Antimony Sulfoiodide for Stable and Lead-free Solar Cells

Summary The quaternary chalcogenide halides of group IV and V elements have attracted much attention due to their interesting semiconducting properties as well as a suitable band gap for solar cells. Here, for the first time, we report on solar cells using tin-antimony sulfoiodide (Sn2SbS2I3). Sn2SbS2I3 solar cells were fabricated using a chemical single-step deposition process with a solution containing a SbCl3-thiourea complex and SnI2 with the configuration of TiO2 and poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]dithiophene)-alt-4,7-(2,1,3-enzothiadiazole)] as the electron- and hole-transporting layers, respectively. The best-performing cell exhibits a power conversion efficiency of 4.04% under the illumination of standard AM 1.5G conditions (100 mW cm−2). These unencapsulated cells exhibited good stabilities at 80% relative humidity, 85°C in air, and under illumination, respectively. These results provide guidelines for fabrication of lead-free heteroleptic perovskite solar cells by hosting divalent or combinations of monovalent and trivalent metal cations.

Influence of Tabula Rasa on Process- and Light-Induced Degradation of Solar Cells Fabricated From Czochralski Silicon

Monocrystalline Si solar cells are fabricated from Czochralski (Cz) Si, which contains 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</sup> -10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">18</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> oxygen atoms. Cz Si undergoes degradation during high-temperature thermal processing steps, such as dopant diffusion to form the p-n junction. This degradation in the bulk minority carrier lifetime can be related to the formation of oxygen precipitates. We found that a high-temperature annealing process known as tabula rasa (TR) not only mitigates process-induced degradation via oxygen precipitate nuclei dissolution, but also modifies subsequent light-induced degradation. We report on the bulk carrier lifetime of n- and p-type Cz Si after TR, which homogenizes the interstitial oxygen in the bulk Si to its monoatomic form in either an N2 or O2 environment. A control sample, which was not subjected to a TR processing step, experienced severe process-induced degradation during a boron emitter thermal budget as oxygen precipitates were formed in the Si bulk. These precipitates could be imaged using photoluminescence. Additionally, samples that underwent a TR processing step prior to the boron emitter thermal budget show efficient gettering of metallic impurities compared to the control sample, which showed a decline in the implied open-circuit voltage after the gettering step. Furthermore, modification of the interstitial oxygen bonding by TR had a strong effect on the light-induced degradation kinetics. Instead of a typically observed monotonic decrease, minority carrier lifetime increases first, followed by a nonmonotonic decrease over a ~20 h period. We conclude that by modifying the interstitial oxygen bonding via TR pretreatment, p-type Cz Si wafers become substantially resistant to harsh solar cell processes and strongly modified light-induced degradation, which would open alternative ways to mitigate this degradation mechanism.

From Generation to Extraction: A Time-Resolved Investigation of Photophysical Processes in Non-fullerene Organic Solar Cells

Non-fullerene organic solar cells (NFOSC) demonstrate record efficiencies exceeding 16%. In comparison with cells with the fullerene-based acceptor, the NFOSC benefit from a longer wavelength absor...

Regulated Crystallization of FASnI3 Films through Seeded Growth Process for Efficient Tin Perovskite Solar Cells

Although rapid progress has been made in tin-based perovskite solar cells (PSCs), the inferior film qualities of the solution-processed perovskites always lead to poor reproducibility and instability. Herein, we present a simple seeded growth (SG) approach to obtain high-quality tin-based perovskite films with preferred crystal orientation, large grain sizes, and fewer apparent grain boundaries. High-quality tin-based perovskite films fabricated through this SG process could greatly reduce the nonradiative recombination centers and inhibit the oxidation of Sn2+. Using formamidinium tin tri-iodide (FASnI3) perovskites, the SG-PSCs exhibit a much improved efficiency from 5.37% (control) to 7.32% with all improved photovoltaic parameters. Moreover, this SG strategy is easily applicable to other tin-based perovskite compositions. The PSC based on methylammonium (MA) doped mixed-cation perovskite (FA0.75MA0.25SnI3) exhibited a power conversion efficiency (PCE) of 8.54% with an improvement of 19.3% in the photovoltaic performance, making it a general approach for achieving efficient tin-based PSCs.

Enhanced current collection of CdTe solar cells in the long wavelength region by co-evaporation deposition CdSexTe1-x films

Using a gradient band gap absorption layer to ensure high short-circuit current density is one of the key factors to prepare high-efficiency CdTe solar cells. CdSexTe1-x films with different selenium compositions were prepared by vacuum co-evaporation deposition technology. The effects of composition changes on the structure, morphology and properties of the films were studied. CdSexTe1-x films were incorporated into the CdTe solar cells with the structure of Glass/SnO2:F/CdS/CdSexTe1-x/CdTe/ZnTe:Cu/Au. The results show that the structure of CdSexTe1-x films is cubic when x is 0, 0.23 or 0.41, and while x is 0.61, 0.78 or 1 the structure is hexagonal. The minimum optical band gap is 1.40 eV with x = 0.41. It is found that in the long wavelength region, the cut-off edge of quantum efficiency curve depends on not only the thickness of CdSexTe1-x film with specific Se composition, but also the whole preparation process of solar cells. After using a 70 nm CdSe0.41Te0.59 film and 70 nm ZnTe:Cu back contact buffer layer, the cut-off edge of the long wavelength region can be reduced to 1.40 eV and the short-circuit current density of the device without antireflection layer reaches up to 28.8 mA/cm2.

Intense pulsed light in back end processing of solar cells with passivating contacts based on amorphous or polycrystalline silicon layers

Intense pulsed light (IPL) is capable of entirely replacing thermal annealing (curing and contact formation) within back end processing of silicon solar cells with passivating contacts. In order to demonstrate this, full-size silicon heterojunction (SHJ) cells with IPL-processed screen-printed metal contacts are fabricated. The device with the highest conversion efficiency reaches 23.0%, which is confirmed by Fraunhofer ISE CalLab. On average, IPL-annealed SHJ cells outperform their thermally treated pendants by 0.3–0.4%abs, in particular due to higher open-circuit voltages and fill factors. To further exploit the potential of IPL, it is applied to tunnel oxide passivating contacts (TOPCon). 2 cm × 2 cm-sized p-type solar cells with TOPCon layers on both sides are fabricated. On the front they exhibit indium tin oxide (ITO) layers as well as screen-printed metal contacts which are either thermally or IPL-annealed. The trade-off between low contact resistivity at the TOPCon/ITO interface and high-quality surface passivation (open-circuit voltages of up to 709.4 mV) is balanced, which is a current challenge for the optimization of such devices. The IPL-processed cells’ series resistances do not differ significantly from those of thermally treated ones. Due to the pulse durations of several milliseconds only, IPL is very fast and offers a high throughput and, therefore, cost saving potential.

Improved the Performance and Stability at High Humidity of Perovskite Solar Cells by Mixed Cesium-Metylammonium Cations

Perovskite solar cells have a great potential as competitor of silicon solar cells which have been dominated the market of solar cells since last decade, due to a tremendous improvement of their power conversion efficiency (PCE). Recently, a PCE of perovskite solar cells above 23% have been obtained. Moreover, perovskite solar cells can be fabricated using simple solution methods, therefore, the whole cost production of solar cells is less than half of silicon solar cells. However, their low stability in thermal and high humidity hinder them to be produced and commercially used to replace silicon solar cells. Many efforts have been done to improve both PCE and stability, including mixed inorganic-organic cations, mixed halide anions, improvement of perovskite morphology or crystallinity and using small molecules for passivation of defect in perovskite. In this paper, we used mixed cesium-methylammonium to improve both PCE and stability of perovskite solar cells. Cesium was used due to its smaller ionic radius than methylammonium (MA) ions, therefore, the crystal structure of perovskite is not distorted. Moreover, perovskite cesium-lead-bromide (CsPbBr3) are more stable than that of MAPbBr3 and doping cesium increased light absorption in perovskite MAPbBr3. We studied the effect of mixed cesium-MA on the PCE and stability at high humidity (&gt;70%). The percentage of cesium was varied at 0%, 5%, 10%, 15% and 20%. The perovskite solar cells have monolithic hole-transport layer free (HTL-free) structure using carbon as electrode. This structure was used due simple and low cost in processing of solar cells. Our results showed that by replacing 10% of MA ions with Cs ions, both PCE and stability at high humidity are improved.

Optimization of ohmic contact on n-type GaAs by screen-printing silver paste

We used printed electronics technology to print silver paste (SP) on n-GaAs as an electrode replacing conventional alloy electrodes to simplify the fabrication process of solar cell and to reduce cost. The linear transmission line model was used to characterize the performances of SP/semiconductor ohmic contact at different annealing temperatures. The lowest specific contact resistance between SP and n-GaAs of 1.8 × 10−4 Ω cm2 was achieved after annealing at 560 °C, which indicates the appropriate annealing temperature can not only ensure the close contact of silver particles, but also reduce the barrier height of metals and semiconductors to a certain extent. On the basis of these results, n-GaAs with an SP electrode can be promisingly applied to realize highly efficient and simple-manufacturing III–V solar cells.

Prediction of key photoelectric parameters at the interface of new subAPPC/C60 organic solar cell

In organic solar cells (OSCs), morphology at the interface between donor and acceptor always have important impact on their performance. Unfortunately, it is always hard to measure and explore the morphology and electronic structure at the interface experimentally. In this paper, subazaphenalenephthalocyanine (subAPPC), a derivative of popular boron subphthalocyanine chloride (subPC) with a core-expanded six-membered ring, is selected to pair with C60 fullerene. The purpose is to explore how the molecular arrangements at donor-acceptor interface influence the optoelectronic properties of this new OSC and to test whether this new solar cell is superior to popular subPC/C60 solar cell because subAPPC seems to have great potential. Then, by modeling five configurations (B/U stands for C60 on/in the convex/concave of subAPPC, respectively), the calculated results of density functional theory (DFT) and time-dependent DFT show that different molecular orientations have significant effects on interfacial photovoltaic properties such as absorption spectrum, open circuit voltage, and exciton binding energy. Finally, new subAPPC/C60 solar cell may be superior to prototype subPC/C60 because simulated absorption is enhanced and predicted VOC could be higher at the interface of B configurations. However, in U configuration, subAPPC/C60 has a very low VOC, which suggest that U configuration should be prevented during fabrication process of this new solar cell.

A pressure process for efficient and stable perovskite solar cells

Abstract The grain boundaries of organic-inorganic halide perovskite films not only function as defect centers, but also behave as intrinsic ion migrating channels and extrinsic moisture-induced degradation initiators, which are detrimental to the efficiency and stability of perovskite solar cells (PSCs). Here, an effective methodology for fabrication of high-quality perovskite layers with reduced non-radiative recombination, suppressed ion migration and increased moisture stability is reported for the first time, referred as the pressure-assisted solution processing (PASP). Through PASP strategy, the nucleation and growth of perovskite crystals can be controlled, leading to the micron-sized grains and microsecond-range carrier lifetimes. The resultant PSC shows champion power conversion efficiency (PCE) as high as 20.74% and a stabilized efficiency exceeding 20%, with superior long-term stability, maintaining above 90% of initial PCE even aging 60 days and continuous 1-sun illumination for 200 h in ambient environment without encapsulation. We unambiguously believe that the control of perovskite crystal nucleation and growth with high quality will be an important direction to improve the efficiency of PSCs to the theoretical limit, as well as to stabilize perovskite-based materials and devices.

The Use of Lasers at Various Stages of the Manufacturing Process of Solar Cells Based on Crystalline Silicon

The purpose of this chapter of the book is to present knowledge on the use of laser technology in silicon photovoltaic cell manufacturing processes. Particular consideration was given to the technique of using a disk laser to cut the edges of silicon wafers together with the recognition of the flow of laser micromachining on the quality of cut edges to obtain their minimal deformation. The second topic described is the method of producing point contacts employing laser radiation between a layer of vaporised aluminium and crystalline silicon using the Nd:YAG laser. The results illustrating the impact of the structure and parameters of point contact for a given laser radiation energy on basic electrical parameters for complete, prototype solar cells are included. The chapter in the book provides an overview of the literature on the above topics and presents selected results of experimental works carried out by the authors. The motive for its publication is the need to present selected results of own research carried out in the Welding Department cooperating for many years with the Institute of Engineering and Biomedical Materials (IMIiB) of the Silesian University of Technology and the Institute of Metallurgy and Materials Engineering (IMIM) of the Polish Academy of Sciences in Cracow.

In Situ Surface Temperature Measurement in a Conveyor Belt Furnace via Inline Infrared Thermography.

Measuring the surface temperature of objects that are processed in conveyor belt furnaces is an important tool in process control and quality assurance. Currently, the surface temperature of objects processed in conveyor belt furnaces is typically measured via thermocouples. However, infrared (IR) thermography presents multiple advantages compared to thermocouple measurements, as it is a contactless, real-time, and spatially resolved method. Here, as a representative proof-of-concept example, an inline thermography system is successfully installed into an IR lamp powered solar firing furnace, which is used for the contact firing process of industrial Si solar cells. This protocol describes how to install an IR camera into a conveyor belt furnace, conduct a customer correction of a factory calibrated IR camera, and perform the evaluation of spatial surface temperature distribution on a target object.

Efficient Se‐Rich Sb2Se3/CdS Planar Heterojunction Solar Cells by Sequential Processing: Control and Influence of Se Content

Quasi‐1D chalcogenides are under the spotlight due to their unique properties for several technological applications including computing, photonic, sensing, and energy conversion. In particular, antimony chalcogenides have recently experienced incredible progresses as emerging photovoltaic materials. Herein, the fabrication by a sequential process of Sb2Se3 solar cells is addressed, and the annealing temperature is found to be the main parameter controlling the composition of the Se‐rich absorbers. Building on this, a systematic study of the evolution of the optoelectronic parameters of the solar cells as a function of the Se excess is presented together with a thorough characterization of the devices that sheds light on their main limiting factors. A record power conversion efficiency of 5.7% is achieved, the highest reported value using reactive annealing on a metallic precursor for this material.

Optimization and characterization of silicon nano-grass antireflection layer on textured silicon wafer

We propose in this paper silicon nano-grass layer as an alternative of conventional black silicon nanowire structure. Conventional metal-assisted chemical etching process by HF produces porous silicon nanowire structure. This is due to uncontrollable chemical reaction making long-heighted nanowires which causes detrimental effect on further solar cell processing. The shape and height of silicon nanostructure was reduced by new chemical solution to minimize the porosity. Silicon nano-grass layer was grown on textured silicon surface and investigated in detail. The structure was formed by NH4F/H2SO4/H2O2 solution at room temperature. Substantial reflectance reduction with broadband spectral range was observed. The etching mechanism and the effect of etch constituents of the etching solution on the structure of nano-grass were studied elaborately. Reflectance and photoluminescence were studied accordingly, and the variations in the surface porosity and light absorbance property have been monitored. At the very end, a comparative study of conventional black silicon etching process by HF/H2O2 and nano-grass on textured silicon by NH4F solution has been investigated. The etch rate and the optical superiority of nanostructures formed by both the solutions have been manifested and explained. For the commercial production level, silicon nano-grass structure is much persistent than silicon nanowire.

Green Solution-Bathing Process for Efficient Large-Area Planar Perovskite Solar Cells.

Perovskite solar cells (PSCs) toward practical application relies on high efficiency, long lifetime, low toxicity, and device up-scaling. To realize large-area PSCs, a green solution-bathing strategy is delivered to prepare high-performance PSCs. By utilizing 2-pentanol as a green solvent and formamidinium chloride (FACl) as a solute in the green solution-bathing process, perovskite films with enlarged grain sizes, improved crystallinity, and alleviated defect state density were obtained, resulting in the enhancement in the power conversion efficiency of PSCs. Coupled with 2-pentanol and FACl, both a champion efficiency of 21.03% for small cells (0.103 cm2) and an efficiency of over 18% for large size (1.00 cm2) were obtained based on the GSB process, which can outperform its counterpart made via the commonly used antisolvent-dropping method. In addition, a large perovskite film (5 cm × 5 cm) with obvious mirror effect was successfully prepared. Our innovative approach paves the way to promote device up-scaling of PSCs via an environmentally friendly technique.

(Invited) Rare Earth Doped Layers Fabricated By Atomic Layer Deposition

Many approaches, developments, structures and materials have been proposed these last years to offer innovative solutions allowing the decrease of the CO2 production and the energy consumption while increasing the efficiency of the properties which are aiming for. Over the last decade, among the approaches developed, a growth process has experienced an important boom related to the possibility it offers on the development of high quality layers. It concerns the Atomic Layer Deposition technique (ALD) that allows growing conformal layer on a substrate having high surface/volume ratio. Although such a technique is well developed and used for microelectronic and photovoltaic applications, the works on photonic devices are still at an early stage. Indeed, for the former, Al2O3, SiNx, HfO2 materials are currently deposited using ALD for microelectronic devices. Besides, the high quality alumina passivation layer is deposited on the Si solar cell bottom that allows the increase of the performance of the solar cell. However, for photonic devices, the crucial issue is to succeed in incorporating and managing the dopant concentration during the process.ALD process is a, at least, two steps process requiring a precursor containing the element of the layer to grow and oxidation step. The most used sequence for Al2O3 growth is a trymethylaluminium (TMA) precursor pulse followed by an oxidation step using water pulse. For doping such layer, a suitable precursor allowing to grow a dopant atomic layer in a temperature range and under oxidizing conditions that are appropriate with the host matrix growth has to be found.The objective of this paper is to present our recent investigations on the growth of RE-doped Al2O3 layer by ALD using different RE precursors. For growing such doped layer, four steps process is required corresponding to the TMA precursor/oxidation sequence followed by the RE-precursor/oxidation one. Fabrication conditions using either water, O2 plasma or ozone as oxidant agent have been investigated to find the ALD window leading to a suitable Growth Per Cycle (GPC) rate in a low deposition temperature range. After deposition, different annealing treatments have been applied to optimize the microstructural and the optical properties of the films considering their potential application, notably in photovoltaic domain. The most attention was paid to Tb- and Er-doped Al2O3 thin layers growth and to the optimization of the processing conditions to achieve required optical properties for the photon management in solar cell.As an example, Er-doped Al2O3 layers have been produced varying the number of Er precursor cycles with respect to the TMA one in order to manage the Er concentration in the layer. Our thin films containing 4.0 to 13 at.% of Er in the host matrix were found to be homogeneous not only prior to the annealing treatment but also after an annealing at 650°C during 15 minutes in nitrogen, conditions that are suitable for solar cell processing. For the highest concentration, phase separation has been observed upon annealing temperature at high temperature. Photoluminescence and photoluminescence excitation experiments have been carried out to study the optical response of such a layer. Indeed, considering that 100nm-thick Al2O3 ALD layer is actually used at the bottom of the Si Cell, succeeding to incorporate optically active Er ions in such a layer and achieving an upconversion process to convert the IR non-absorbed photons by the cell would be a way to increase the Si cell efficiency without modifying a well-established industrial process.