Thin Film Heterojunction Solar Cells Research Articles

Influence of Deposition Parameters on Performance of Zn(O,S) Buffer Layer Deposited by Solution-Based Continuous Flow Reactor for CIGS Solar Cells

CdS thin films are commonly used as buffer layers in hetero-junction structured CIGS thin film solar cells. However, the toxicity of Cd has raised concerns regarding environmental safety and alternative materials have been explored. ZnS is a leading candidate to replace Cd, with the presence of Zn(O,S) impurities known to be required for efficient CIGS solar cell fabrication. In this study, we synthesized Zn(O,S) films using a solution-based deposition method combining a continuous flow reactor (CFR) with another solutionbased deposition method. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the structural and physicochemical properties of the films, confirming the efficacy of the CFR process for depositing Zn(O,S) thin films in a short period of time. We successfully deposited Zn(O,S) thin films using the combined CFR process. Cd-free B:ZnO/Zn(O,S)/CIGS solar cells were fabricated on Mo-coated glass substrates to investigate the effects of experimental parameters, such as deposition time and method, on the performance of the Zn(O,S) buffer layer in the devices.

Comparative study by simulation betweentwo structures CdS/CZTS and ZnS/CZTS via SCAPS-1D software

This comparative numerical simulation study investigates the electrical characteristics of two heterojunction thin-film solar cells based on Kësterites Copper Zinc Tin Sulfide. The study compared two solar cells with different structures, Zinc Oxide ZnO/Cadmium Sulfide CdS/Kësterites CZTS/Molybdenum Mo and Zinc Oxide ZnO/Zinc Sulfide ZnS/Kësterites CZTS/Molybdenum Mo, to determine which is more efficient in achieving maximum photovoltaic efficiency. The results showed that the ZnO/ZnS/CZTS/Mo solar cell is the better option, outperforming the CdS/CZTS/Mo solar cell in terms of short-circuit current density Jsc, open-circuit voltage Voc, form factor FF, and photovoltaic efficiency η. The study also investigated the effect of doping and layer thickness of CZTS and ZnS on photovoltaic parameters. The optimized ZnS/CZTS solar cell achieved an efficiency of 16.29% for ZnS and CZTS layer thicknesses of 0.02µm and 4μm, respectively, and doping concentrations of 1018 and 1016cm-3 , respectively. Overall, this study provides valuable insights for designing more efficient solar cells and optimizing their photovoltaic efficiency using Kësterites CZTS, CdS, and ZnS materials.

Recent Advances and Prospects of Solution‐Processed Efficient Sb2S3 Solar Cells

AbstractSolar cells comprising earth‐abundant and non‐toxic elements with applicable bandgaps and high absorption coefficients have attracted considerable interest over the past several decades and are important devices for addressing the future demand for clean and renewable energy. Antimony sulfide (Sb2S3) crystal material effectively meets these requirements owing to its suitable bandgap, high absorption coefficient, high electron and hole mobilities, earth abundance, and excellent stability. Solution‐processed Sb2S3 films are essential to facilitate the fabrication of low‐cost, large‐scale, and high‐efficiency photovoltaic devices, but suffer from several shortcomings of large intrinsic defects, high interfacial barrier, and atomic mismatch, uncontrollable film thickness, and crystal orientation. In this review, a systematic overview of the fundamental properties of solution‐processed Sb2S3 materials is presented, and then interface engineering, defect passivation and control strategies, crystal orientation and modulation methods, device structure, and the performance of Sb2S3 solar cells are focused, highlighting the primary advancements and major challenges based on this technology. Finally, several creative perspectives and constructive innovation strategies for future research on Sb2S3 photovoltaic devices are provided, indicating a roadmap for the practical application of other inorganic semiconductor heterojunction thin film solar cells.

A CTL-free homo-heterojunction antimony chalcogenide solar cell: Theoretical study

Exploring antimony chalcogenide as photovoltaic (PV) absorber material for solar cell is an appealing strategy. However, the conversion efficiency (η) of antimony chalcogenide solar cells including antimony selenide (Sb2Se3), antimony sulfide (Sb2S3) and antimony sulfide–selenide (Sb2(S,Se)3) lag far behind their Shockley−Queisser limit efficiency. Generally, the device PV performance of thin film heterojunction solar cells is mainly affected by the material properties of each functional layer, as well as the device architecture and heterointerface characteristics. Herein, a novel homo-heterojunction antimony chalcogenide solar cell without any carrier transport layer (CTL) consisting of FTO/(n)Sb2Se3/(p)Sb2Se3/(p)Sb2S3/Metal has been proposed. The influence of thickness, doping concentration and bulk defect density of the functional layer materials, the interface defect density at (p)Sb2Se3/(p)Sb2S3 heterointerfaces, and back contact metal work function on device PV performance have been theoretically analyzed utilized wxAMPS software. After optimization, the proposed solar cell has an open-circuit voltage (Voc) of 0.885 V, a short-circuit current density (Jsc) of 36.14 mAcm−2, a filling factor (FF) of 84.30 %, and a η of 26.97 %. These results indicate that the novel homo-heterojunction antimony chalcogenide solar cell without any CTL have the potential to become a high-efficiency PV device.

Bottom-up self-assembly of macroporous ZnO nanostructures for photovoltaic applications

The present study utilized a template-assisted electrodeposition route for the bottom-up epitaxial growth of macroporous zinc oxide nanostructures. To this end, the ZnO seed layer was coated on the p-type silicon substrates using a radio frequency magnetron sputtering technique to form a p-n heterojunction. Then, polymer microspheres were implanted on ZnO/Si substrates to act as a template. Subsequently, ZnO nanostructures were electrodeposited through the interstitial spaces between the microspheres. After the deposition, the microspheres were removed by dissolving in chloroform solvent, forming a porous structure. The planar and cross-sectional electron microscopy analyses exhibited a uniform macroporous morphology with an average pore diameter of ∼1 μm. The pores were homogeneously distributed on the surface of the electrodeposited ZnO layer. The advantage of this technique over the top-down approaches, such as electrochemical etching, is that the porosity and size of pores can be easily adjusted by varying the concentration and diameter of microsphere templates. The optical investigations revealed enhancement in photon absorption and photoluminescence (PL) intensity due to multiple light scattering in the pore walls of the deposited ZnO nanostructures. For the templated sample, a PL blue shift was observed due to the reduction in crystallite size of ZnO nanostructures. A heterojunction thin film solar cell was designed by the metallization of ZnO/p-Si samples to study the power conversion capability of macroporous ZnO nanostructures. The photovoltaic performance of the developed devices was evaluated under a solar light simulator. The device based on the templated sample showed increased shunt resistance and reduced series resistance compared to the flat sample. The optoelectrical results indicated an efficiency improvement for the fabricated solar cells based on the macroporous ZnO sample due to its higher exposed area and increased rate of electron-hole generation.

Effect of feeding flow rate on characteristics of CuInSe2 films prepared by flash evaporation

Copper indium selenide CuInSe2 (CISe) is one of the most promising absorber materials in high efficiency heterojunction thin-film solar cells due to its high conversion efficiency and known high stability. This paper describes a simple method for preparing CuInSe2 films from pre-prepared CuInSe2 ingot powder using a flash evaporation method. The primary goal of this work is to investigate the effect of feeding flow rate on CuInSe2 film characteristics. The powder feeding flow rate into the evaporator has been adjusted to control the film growth rate. Structure, composition, morphology, electrical and optical properties have all been studied for films deposited at different feeding flow rates. The results show that varying the feeding flow rate affects film characteristics, and that lower feeding rates yield films with better characteristics, which should be considered in future semiconductor film processing.

Performance analysis of n-TiO2/p-Cu2O, n-TiO2/p-WS2/p-Cu2O, and n-TiO2/p-WS2 heterojunction solar cells through numerical modelling.

A new hetero-structure of n-TiO2/p-WS2/p-Cu2O is proposed as a potential candidate for solar energy generation using tungsten disulfide (WS2) as an absorber layer. The proposed device performance is simulated by employing a one-dimensional solar cell capacitance simulator (SCAPS-1D). The numerical simulation studies compared the performances of n-TiO2/p-Cu2O, n-TiO2/p-WS2/p-Cu2O, and n-TiO2/p-WS2 hetero-structures based on various physical parameters like interface defects density, bulk defects density, absorber layer thickness, series resistance, shunt resistance, and operating temperature. In our simulation investigations, we found that interface defects pose a formidable impact on heterojunction devices. Interface defects closer to the front surface severely deteriorate the performances than the back surface. The bandgap of the absorber layer influences the performances of the solar cells. A closer comparison between n-TiO2/p-Cu2O and n-TiO2/p-WS2 heterojunction solar cells (HJSCs) revealed that the latter (n-TiO2/p-WS2) has nearly 182% better performance than the former (n-TiO2/p-Cu2O) devices. Additionally, the performance of the n-TiO2/p-WS2 solar cell is further boosted by ~ 139% in the presence of a hole transport layer of p-Cu2O. The best-simulated efficiency of the proposed new hetero-structure (n-TiO2/p-WS2/p-Cu2O) solar cell is 28.86%. Moreover, these optimized physical parameters may shed light on "easy to apply" new path for fabrication of a non-toxic, environment-friendly, and highly efficient novel thin-film heterojunction (n-TiO2/p-WS2/p-Cu2O) solar cell.

Cu2ZnSnS4 thin-film solar cells by a closed tube sulfurization under saturated sulfur vapor pressure

CdS/Cu2ZnSnS4 (CZTS) heterojunction thin-film solar cells were fabricated via a closed tube sulfurization under saturated sulfur vapor pressure. A significant improvement in the crystalline quality of the CZTS polycrystalline thin-film was achieved when the Cu–Zn–Sn metallic-alloy thin-film was sulfurized under saturated sulfur vapor pressure of 4.3 atm at 590 °C due to efficient suppression of re-evaporation of Zn and Sn species during the growth process. Accordingly, the open-circuit voltage and short-circuit current density of the CdS/CZTS heterojunction device were enhanced resulting in the improvement of power conversion efficiency by over 1.7 times compared to the best cell fabricated by the conventional processes under unsaturated sulfur vapor pressure of 1.5 atm.

Deposition of Cu2ZnSnS4 thin film at different solution flow rates

A thin film of Cu2ZnSnS4, a potential compound semiconductor for the absorber layer in thin film heterojunction solar cells, has been successfully deposited using the spray pyrolysis process. The influence of solution spray rate on deposited film characteristics is investigated. The structural and optical properties of the films have been studied. X-ray diffraction studies revealed the films are polycrystalline in nature with the kesterite structure and the lattice parameters are found to be a = b = 0.542 nm and c = 1.082 nm. Micro Raman spectra confirm the Cu2ZnSnS4 crystal phase. Optical band gap, evaluated from spectral transmittance data, which is close to 1.5 eV. The absorption coefficient of these films is ≥ 104 cm−1. These films are found to be p-type in nature. Finally, work on fabricating a conventional thin film heterojunction solar cell has been undertaken.

Improved n-ZnO nanorods/p-Si heterojunction solar cells with graphene incorporation

The present research explored the effect of graphene layer and zinc oxide nanorods (NRs) on the photovoltaic performance of ZnO thin film-based heterojunction solar cells. For this purpose, ZnO thin film was deposited on p-type silicon using radio frequency sputtering to serve as an anti-reflective layer and n-type semiconductor to form a heterojunction thin film solar cell. Then, a cost-effective and facile chemical bath deposition technique was employed to synthesize ZnO NRs. To study the effect of reduced graphene oxide (rGO) on the optical properties of ZnO NRs, the colloidal suspension of rGO and ZnO NRs (rGO:ZnO NRs) was prepared. The optimized nanostructures were then transferred to the surface of the ZnO/Si sample using a drop-cast method. The morphological examination of the nanostructures showed the formation of ZnO NRs with various orientations which can significantly increase the entrapment of incident photons. The XRD results indicated an improvement in the structural properties of ZnO NRs upon adding rGO flakes. The reduction of GO was confirmed using Raman spectroscopy. The higher ID/IG ratio for the rGO:ZnO NRs sample (compared to GO layers) suggested the chemical reduction of GO. The optical investigations revealed an increment in the light absorption and PL intensity in the rGO-containing samples which can be due to the role of graphene as a reinforcement phase to inhibit the electron-hole recombination. The optoelectrical properties of fabricated solar cells were investigated via the metallization of top and rear contacts to fabricate three different solar cells based on ZnO thin film, ZnO NRs, and rGO:ZnO NRs. The results showed an enhancement in the efficiency (14.12%) and the fill factor (0.552) of the solar cell based on rGO:ZnO NRs compared to the other solar cells. Therefore, the incorporation of rGO can improve the photovoltaic properties of solar cells based on ZnO nanorods.

Tailored Band Structure of Cu(In,Ga)Se2 Thin-Film Heterojunction Solar Cells: Depth Profiling of Defects and the Work Function.

An efficient carrier transport is essential for enhancing the performance of thin-film solar cells, in particular Cu(In,Ga)Se2 (CIGS) solar cells, because of their great sensitivities to not only the interface but also the film bulk. Conventional methods to investigate the outcoming carriers and their transport properties measure the current and voltage either under illumination or dark conditions. However, the evaluation of current and voltage changes along the cross-section of the devices presents several limitations. To mitigate this shortcoming, we prepared gently etched devices and analyzed their properties using micro-Raman scattering spectroscopy, Kelvin probe force microscopy, and photoluminescence measurements. The atomic distributions and microstructures of the devices were investigated, and the defect densities in the device bulk were determined via admittance spectroscopy. The effects of Ga grading on the charge transport at the CIGS-CdS interface were categorized into various types of band offsets, which were directly confirmed by our experiments. The results indicated that reducing open-circuit voltage loss is crucial for obtaining a higher power conversion efficiency. Although the large Ga grading in the CIGS absorber induced higher defect levels, it effectuated a smaller open-circuit voltage loss because of carrier transport enhancement at the absorber-buffer interface, resulting from the optimized conduction band offsets.

Performance investigation of Sb2S3 and Sb2Se3 earth abundant based thin film solar cells

Recently, antimony sulfide (Sb2S3) and antimony selenide (Sb2Se3) materials have received a particular research attention as absorbers in hetero-junction thin film solar cells due to their high optical absorption, low cost, earth abundance, and non-toxic properties. In this work, we investigate numerically Sb2S3 and Sb2Se3 based solar cells and analyze their performance using SILVACO software. A simulation of absorber and buffer layers thickness, radiative recombination coefficient, doping densities in absorbent and buffer regions, defect in absorbent region and at buffer/absorber interface alongside with rear contact metal work function is effectuated in order to optimize these parameters. Absorber's optimal parameters are found to be 1 μm thickness, 10−9 cm3/s radiative recombination coefficient, 5 × 1016 cm−3 acceptor doping density, 1015 cm−3 defect density and 5 eV work function for Sb2S3 and 1.5 μm, 10−9 cm3/s, 1017 cm−3, 1015 cm−3 and 4.5 eV for Sb2Se3. Buffer layer optimal parameters are 20 nm thickness and 1020 cm−3 doping density for Sb2S3 based solar cell and 10 nm and 2 × 1020 cm−3 for Sb2Se3 one. Buffer/absorber interface optimal defect density is 1013 cm−3. PV structures with such optimal parameters give conversion efficiencies of 14.45 and 12.84% for Sb2S3 and Sb2Se3 based solar cells, respectively.

Strategy trends of core/multiple shell for quantum dot-based heterojunction thin film solar cells

ABSTRACT Design structure of semiconductor window and absorber layers’ materials in thin film solar cells is an essential trend for specifying optical and electrical characteristics of thin film solar cells. This paper has been improved the optical and electrical characteristics and efficiency of traditional HJ-QDSc (ITO/CdS/QDPbS/Au) model by using the quantum dot window layer instead of bulk structure layers’ cell. Moreover, this paper represents new design for absorber layer using QD aluminium core/PbS shell absorber layer structure instead of QD PbS absorber layer to use the merits of QD metallic-semiconductor core/multiple shell structure to enhance the performance of previous CdS/QDPbS HJ-QDSc model. The proposal design structure is carried out by replacing the bulk CdTe, CIGS absorber layers and CdS window layer with quantum dot size window layer material and QD core/multiple shell absorber layer based on traditional (SnO2/CdS/CdTe/Cu) and (ZnO/CdS/CIGS/Mo). The proposal design structure on three-types of core/multiple shell for quantum dot based on heterojunction thin film solar cells has been applied. A comparison study has been established between the proposal design and traditional thin film solar cells based on sub-micro absorber layer thickness models.

Influence of the crystal substrate parameters on the maximum power of silicon heterojunction solar cells

The effect of the donor impurity concentration and the lifetime of charge carriers in a crystalline silicon substrate on the maximum power of heterojunction thin-film solar cells is studied. The model used in the calculations takes into account the features of photocurrent generation under conditions of medium or high levels of injection of charge carriers at an arbitrary ratio between the diffusion length and the thickness of the semiconductor wafer. The proposed technique makes it possible, with sufficient accuracy for practical purposes, to calculate the permissible variation limits of the substrate parameters, which ensure the specified values of the performance characteristics of photoelectric converters. Keywords: heterojunction solar cells, crystalline silicon substrates, optimal parameters, maximum power.

Influence of the crystal substrate parameters on the maximum power of silicon heterojunction solar cells

The effect of the donor impurity concentration and the lifetime of charge carriers in a crystalline silicon substrate on the maximum power of heterojunction thin-film solar cells is studied. The model used in the calculations takes into account the features of photocurrent generation under conditions of medium or high levels of injection of charge carriers at an arbitrary ratio between the diffusion length and the thickness of the semiconductor wafer. The proposed technique makes it possible, with sufficient accuracy for practical purposes, to calculate the permissible variation limits of the substrate parameters, which ensure the specified values of the performance characteristics of photoelectric converters. Keywords: heterojunction solar cells, crystalline silicon substrates, optimal parameters, maximum power.

Influence of the oxygen during the deposition of an indium tin oxide thin film by magnetron sputtering for heterojunction solar cells

Optoelectronic properties of indium and tin oxide thin films depending on the oxygen content in the total gas flow were experimentally investigated during deposition of these films by DC magnetron target sputtering. Relationship of the heterojunction thin-film solar cell output parameters vs. oxygen partial pressure in a vacuum vessel was examined during indium and tin oxide layer deposition. The maximum photovoltaic conversion efficiency of the solar cell was achieved at an oxygen partial pressure in the vacuum vessel of ~6.5 Torr. Keywords: heterojunction thin-film solar element, indium and tin oxide, magnetron sputtering.

Benefits of Low Electron-Affinity Material as the N-Type Layer for Cu(In,Ga)S2 Solar Cell

Despite the potential in single- and multi-junction solar cells application, research into the wide band gap CuIn1−xGax(Se1−ySy)2 or CIG(SSe)2 solar cell material, with Eg≥1.5eV, has yet to be extensively performed to date. In this work, we conducted a numerical study into the role of the n-type layers in CIG(SSe)2 heterojunction solar cells, specifically concerning the maximum open-circuit voltage of the devices. In the first part of the study, we derived a new ideal open-circuit voltage equation for a thin-film heterojunction solar cell by taking into account the current contribution from the depletion region. The accuracy of the new equation was validated through a simulation model in the second part of the study. Another simulation model was also used to clarify the design rules of the n-type layer in a wide band gap CIG(SSe)2 solar cell. Our work stressed the importance of a positive conduction band offset on the n-/p-type interface, through the use of a low electron affinity n-type material for a solar cell with a high open-circuit voltage. Through a precise selection of the window layer material, a buffer-free CIG(SSe)2 design is sufficient to fulfill such conditions. We also proposed the specific roles of the n-type layer, i.e., as a passivation layer and selective electron contact, in the operation of CIGS2 solar cells.

Numerical modeling of copper indium disulfide thin film based solar cells

In this work we have modeled CuInS 2 based solar cells. CuInS 2 is a p-type semiconductor which is used as an absorber layer in the heterojunction thin film solar cell ZnO:Al/i-ZnO/CdS/CuInS 2 /Mo. Numerical modeling was done by SCAPS-1D. The simulation focuses on studying several effects on photovoltaic parameters; open circuit voltage, density of short circuit, fill factor and efficiency. In a first step we have studied temperature effect; the performance of the cell decreased because of the decrease of open circuit voltage due to the rise of reverse current, in the other hand the fill factor increases at high temperature which is the same behavior of Silicon based solar cells. Thickness of the absorber layer has been varied too, 2.5 μm of thickness is the optimum value chosen instead of higher thickness in order to have a compromise between cost and efficiency. After that we decided to design a Cadmium free cell by replacing Cadmium Sulfide (CdS) layer with Tin Disulfide (SnS 2 ). However, cadmium layer showed better efficiency than SnS 2 . Then we discussed the importance of back surface field layer (Cu 2 O), whom insertion leads to improve the efficiency to 22.73% compared to the efficiency obtained by the conventional structure 12.64%. • New structures ZnO:Al/i-ZnO/CdS/CuInS 2 /Cu 2 O/Mo and ZnO:Al/i-ZnO/SnS 2 /CuInS 2 /Cu 2 O/Mo have been modeled. • The ZnO:Al/i-ZnO/CdS/CuInS 2 /Cu 2 O/Mo showed a good stability under temperature varied from 300 K to 325 K. • An efficiency of 22.73% have been achieved with ZnO:Al/i-ZnO/CdS/CuInS 2 /Cu 2 O/Mo. • The Cadmium free structure ZnO:Al/i-ZnO/SnS 2 /CuInS 2 /Cu 2 O/Mo showed an efficiency of 21.62%.

Numerical study of semi-transparent thin film heterojunction p-CuO/nZnO/AZO/ITO solar cells device model using SCAPS-1D

In the current time, transparent and semitransparent solar cells in photovoltaic industry have drawn important attention owing to their potential use as solar windows, and energy harvesting devices for building, vehicle integration and flexible electronics. In this work, a semitransparent thin film heterojunction solar cells device structure of p-CuO/nZnO/AZO/ITO was numerically modeled using SCAPS-1D software tools. The cell’s performance was investigated in terms of the different material layer properties, such as the thickness and carrier concentration or doping level. The simulation results of copper based semi-transparent thin film solar cell (TFSC) as the bottom cell model indicates that the highest efficiency was achieved at 8.9116 %, with the thickness and carrier concentration of n-ZnO material layer set at 20 nm, and 5.0 x 1018 cm-3 respectively, whereas the thickness of CuO absorber layer was fixed at 110 nm. Finally, the overall results show that CuO based absorber layer exhibits potential as photoactive material particularly for semitransparent thin film solar cells applications.

Photovoltaic performance enhancement in CdTe thin-film heterojunction solar cell with Sb2S3 as hole transport layer

In this work, we design a novel cadmium telluride (CdTe)-based solar structure with antimony sulfide (Sb2S3) as hole transport layer (HTL). One Dimensional Solar Cell Capacitance Simulator (SCAPS-1D) program is used to perform comparison studies on the photovoltaic performances between the standard thin-film cadmium sulfide (CdS)/CdTe solar cell and the proposed Al/FTO/CdS/CdTe/Sb2S3/Ni heterojunction structure. The solar cell outputs such as open-circuit voltage (Voc), short-circuit current density (Jsc), fill-factor (FF), and efficiency have been evaluated by varying impacts of thickness, electron affinity, carrier concentration, and bulk defect density of different layers. In addition, we have analyzed the effect of interface defects at both CdS/CdTe and CdTe/Sb2S3 interfaces. This study reveals that the introduction of Sb2S3 as HTL improves the Voc appreciably by creating appropriate band alignment with the CdTe absorber and thus remarkably enhance the efficiency of solar cell by lowering carrier recombination at back contact surface. Moreover, the impacts of working temperature, back contact metal work function, and surface recombination velocity are elucidated. The absorber thickness is optimized to be 1.0 µm with doping concentration of 2.1 × 1015 cm−3. Best efficiency of 28.41% together with other parameters such as Voc of 1.15 V, Jsc of 28.74 mA/cm2, and FF of 86.03% is achieved for the optimized device. These results lead to suggest that the Sb2S3 as HTL can be employed to fabricate highly efficient and inexpensive thin-film CdTe heterojunction solar devices.