Thin Film Solar Cell Structure Research Articles

Nitrogen doped single layer graphene for CZTS-based thin film solar cells

CdS thin films are commonly utilized as a buffer layer in chalcopyrite thin-film solar cells. However, due to the toxic nature of Cadmium (Cd), ongoing efforts are being directed towards exploring alternative options. In this contribution, doped graphene film with remarkable optical and electrical properties has been introduced for the first time as an alternative buffer layer, replacing CdS in CZTS thin-film solar cell application. In this study, nitrogen-doped graphene (N-doped graphene) film was utilized as a substitute buffer layer in the CZTS thin-film solar cell structure, replacing the conventional CdS thin film. For comparative analysis, CZTS/N-doped graphene and CZTS/CdS traditional solar cell structures were fabricated and separately characterized. The CZTS thin films produced were examined through EDX, XRD, SEM, Raman, optical transmission and PL spectroscopy measurements. According to performed analyses, the Cu-poor and Zn-rich kesterite CZTS thin films exhibited a uniform and dense polycrystalline microstructure as observed in surface and cross-sectional SEM images. XRD spectra of the kesterite CZTS thin film displayed predominant peaks corresponding to the (112), (220/204), and (312/116) diffraction planes of the kesterite CZTS phase. Raman spectra showed a dominant peak at ∼336 cm−1 associated with the kesterite CZTS phase. PL emission spectra indicated transitions from the conduction band to defect levels. The CVD-grown doped graphene film exhibited a 3.43 I2D/IG ratio and a 25 cm−1 FWHM of the 2D peak, indicating a single-layer graphene according to Raman analysis. Permanent nitrogen doping with a 2% atomic concentration was confirmed by XPS measurement. The optical transmission measurement of the single layer doped graphene film showed a 95% transmittance value. Nitrogen doping was contributed to decrease the sheet resistance of the graphene film. The Glass/Mo/CZTS/N-doped graphene/i-ZnO/ITO/Al solar cell displayed a VOC of 0.267 V, JSC of 24.6 mA/cm2, FF of 36.46, and η of 2.37%, showing higher FF and Jsc values but lower conversion efficiency compared to the Glass/Mo/CZTS/CdS/i-ZnO/ITO/Al traditional solar cell structure. Hence, the superior working function and transparency properties position the N-doped graphene film as a competitive buffer layer for use in CZTS-based thin-film solar cells.

A A highly efficient InGaP thin film solar cell structure, optimization and characteristics

Inorganic solar cells based on III-V semiconductor materials are widely used owing to their high efficiencies. In this work, we aim to improve the performance of the single heterojunction solar cell InGaP. The InGaP cell is constituted of a back surface field (BSF), a base, an emitter and a window layer with InAlAsP material. The simulation is done after optimization, modeling, and choice of the used materials and the thickness of different layers constituting the solar cell. The choice of materials whose gap energy is decreasing allows the absorption of the solar spectrum in its almost totality. Then, we varied the temperature to know its effects on the gap energy and the efficiency of the InGaP cell. The InGaP and solar cell with optimal parameters are illuminated by an AM1.5 solar spectrum through InAlAsP window layer. The simulation and optimization at 300K of short circuit current parameters (Jsc), open circuit voltage (Voc), fill factor (FF) and efficiency (?) are done using Tcad Silvaco software. The characteristics obtained are: the minimized thickness of 665 nm, electrical efficiency is about ? = 21.87% for InGaP cell, Jsc = 14.43 mA/cm2, Voc = 1.63 V, and FF = 91.21 %.

Optimisation and numerical analysis of highly efficient CGSe-based thin film solar cell

Among the various chalcopyrites compounds used in photovoltaic devices, Copper Gallium Selenium (CGSe) turns out as an underperformer due to its limited photovoltaic performance, So far highest efficiency measured is about 11.9%. This paper investigates the possibilities for efficiency enhancement for the CuGSe layer in Cu2O/CGSe/TiO2/ZnO thin film solar cell structure using the SCAPS-1D simulation program. The short circuit current (Jsc) and power conversion efficiency (PCE) is 30.77 mA cm−2 and 27.10%, with open-circuit voltage (Voc) and fill factor (FF) of 1.03 V and 84.72% respectively. Furthermore, we evaluated some specific parameters of TiO2/CGSe heterostructure, such as the influence of layer thickness, operating temperature, the effect of defect density and acceptor density of CGSe layer, metal work function, and the effect of series and shunt resistance on cell performance. We investigated that combining TiO2 as an ETL and Cu2O as HTL with a CGSe absorber layer is novel and promising, which results in higher power conversation efficiency and improves other PV parameters. The application of CGSe/TiO2 heterojunction in a simulated model offers a viable method for the development of high-efficiency solar cell devices.

Numerical Study and Optimization of CZTS-Based Thin-Film Solar Cell Structure with Different Novel Buffer-Layer Materials Using SCAPS-1D Software

Numerical Study and Optimization of CZTS-Based Thin-Film Solar Cell Structure with Different Novel Buffer-Layer Materials Using SCAPS-1D Software

Numerical Investigation of High Efficiency Cu₂SnSe₃ Thin Film Solar Cell with a Suitable ZnSe Buffer Layer Using SCAPS 1D Software

As the world’s energy demand continues to grow, thin-film solar cells are poised to play an increasingly important role in meeting that demand. In this research, we have proposed and simulated a high-efficiency Cu2SnSe3- based thin film solar cell structure using a solar cell capacitance simulator (SCAPS-1D) software. The numerical performance of Cu2SnSe3 thin films solar cell with ZnO:Al as the electron transport layer (ETL), ZnSe as the buffer layer, SnS as the hole transport layer (HTL), Ag as the front and Ni as the back contact with the structure (Ag/ZnO:Al/Cu2SnSe3/SnS/Ni) has been studied. This simulation intended to investigate the effect of the ZnO:Al electron transport layer and SnS hole transport layer on the performance of the proposed solar cell. The device was optimized concerning the thickness, temperature, series and shunt resistance, donor density of the Electron transport layer, back contact metal work function, and acceptor density of the Cu2SnSe3-based thin film solar cell. The thickness of the ETL, buffer, absorber, and HTL was optimized to 0.2 μm, 0.05 μm, 1.5 μm, and 0.1 μm, respectively. The proposed cadmium-free Cu2SnSe3 thin films solar cell exhibited a conversion efficiency of 31.04%, VOC of 1.08 V, JSC of 34.11 mA/cm2, and FF of 83.84%. As a result, due to its low cost, earth-abundant, non-toxicity, and high efficiency, the suggested Cu2SnSe3-based solar cell may be an attractive candidate for thin film solar cells.

Impact of tin-based perovskite as a hole transport layer on the device performance of stable and 27.10% efficient CdTe-based solar cell by numerical simulation

In this work, a numerical simulation study on cadmium telluride (CdTe)-based thin film solar cell structure utilizing CdTe as absorber layer, Cadmium sulphide (CdS) as window layer, and lead-free perovskite (CH3NH3SnBr3) as a hole transport layer (HTL) is presented for the first time. The effect of different material parameters such as shallow uniform acceptor density (NA) of absorber and HTL, thicknesses of absorber and HTL, Electron affinity of HTL, defect density of absorber layer, series and shunt resistance, back contact metal work function, and operating temperature on photovoltaic (PV) parameters such as open-circuit voltage (Voc), short circuit current (Jsc), fill factor (FF), and photo conversion efficiency (PCE) has been studied. With the introduction of perovskite as HTL, it is observed that Voc increased from 0.66 V to 1.17 V by creating a suitable band alignment with the CdTe absorber layer, causing an improvement in efficiency by preventing carrier recombination at the back contact surface. The designed solar cell has shown an enhanced PCE of 27.10% with Voc ∼1.17 V, Jsc ∼27.76 mA/cm2, and FF ∼83.40%. Thus, from the study, it is possible to achieve high-performance CdTe-based solar cells using perovskite as HTL for photovoltaic applications.

Numerical modeling and performance analysis of Sb-based tandem solar cell structure using SCAPS – 1D

Antimony sulfo-selenide, Sb2(S-Se)3including Sb2S3 and Sb2Se3 are known as the binary type metal chalcogenides semiconductors. They carry abundant elemental storage which is nontoxic in nature, having good stability at elevated temperature and have acceptable physical specifications regarding light absorbance substances in photovoltaic devices. Exploiting from the earlier study related to thin film devices and from the recent nanostructured photovoltaics, the Sb2S3 and Sb2Se3is being considered as an absorber layer for hetero-junction type planer solar cells or in sensitized-architecture solar cells. To show a perspective of this sphere of study, this paper exhibits some distinctive studies of the physical parameters of the Sb2(S,Se)3 device. In this optimization process, Sb2Se3 and Sb2S3 used as a tandem structure in the conventional thin film solar cell structure. Different parameters like; thickness, radiative recombination, carrier concentration and series/shunt resistance of the device has been optimized using SCAPS-1D software sequentially. After the optimization of all the above discussed parameters, a reasonable power conversion efficiencies of 13.2% was achieved. With the optimized value, how to achieve a device with good PCE is discussed. Finally, this paper analyses a detail study about the performance of antimony sulphide-selenide based tandem solar cell device for photovoltaic applications.

Highly efficient ACdTS kesterite solar cell based on a new photovoltaic material

The quasiparticle band structures and optical properties of ACdTS kesterite are investigated here on the basis of first-principles calculations, including the many-body effects theory, by using the GW plus Bethe-Salpeter equation. There were significant GW-quasiparticle corrections, over 0.9 eV, to the GGA-Kohn-Sham band gap. Our calculations also show that ACdTS kesterite had a small binding energy, exhibited optical absorption in the visible region, high minority carrier mobility, and large diffusion in length, rendering this material a promising candidate for solar cells. Based on these findings, we designed and implemented an ACdTS absorber in a thin-film solar cell (TFSC) structure. The new kesterite solar cell has a high efficiency of 11.6% with a low deficit in the output voltage. Moreover, a strategic combination between the particle swarm optimization approach and the ACdTS TFSC decorated with periodic nanowires is proposed to obtain significantly improved photovoltaic characteristics. The optimized design identifies a new pathway for a high conversion efficiency of 14%, far surpassing that provided by the conventional TFSC kesterite.

Enhancement in photocurrent by dual-interface period-mismatched rotating rectangle grating-based c-Si solar cells.

A dual-interface period-mismatched rotating rectangular grating structure was designed for crystalline silicon thin film solar cells. The relevant parameters of the grating structures were optimized, and the absorption enhancement mechanisms were also explained by optoelectronic simulation analysis. The numerical results show that the rotating rectangular structure can improve the light-trapping performance by coupling light into the c-Si film to excite the waveguide mode and localized surface plasmon resonances. Moreover, it is found that the light-trapping effect of the rear grating rotating structure is better than that of the front grating rotating structure, because the rear interface can better excite localized surface plasmon resonances. The photocurrent density of the dual-interface period-mismatched rotating rectangular grating structure is increased to $18.01\; {\rm mA/cm}^2$, which is 76.05% higher than that of the planar 300 nm thick c-Si structure. The research results provide general guidance for the design of grating structures for thin-film solar cells.

Period-mismatched sine dual-interface grating for optical absorption in silicon thin-film solar cells.

Crystalline silicon thin-film solar cells with period-mismatched sine dual-interface gratings are proposed. Several structural parameters of the front and rear gratings, such as heights, periods, and duty ratios, are optimized using the finite-difference time-domain method. The mechanisms of absorption enhancement are also illustrated by analyzing the optical and electrical performance in thin-film solar cells with different grating arrangements. Numerical results indicate that the period-mismatched sine dual-interface grating structure shows obvious improvement in absorption efficiency and is more suitable for grating structures with small period. The short-circuit current density of the period-mismatched dual-interface sine grating structure is improved to 18.89mA/cm2, an increase of 41.39% as compared with the planar structure. The research findings can be utilized to guide the design of grating structures for thin-film solar cells.

Thin film solar cell efficiency enhancement using a gradient doping absorbent layer

In this contribution, we propose a numeric exploration of a copper indium gallium diselenide (CIGS) based thin film solar cell structure by means of SILVACO's technology computer aided design (T-CAD). We found the performance of our proposed cell and that of experimental champion very similar. High resistance and surface recombination near the rear contact alongside with bulk recombination reduce solar cell performance. In order to get a cell performance enhancement, we suggest the introduction of an additional electric field via gradient doping in absorbent layer in order to reduce the latter phenomenon effects. Therefore, both graded and uniform doping profiles have been studied then compared. Our results demonstrated that the graded doping in CIGS absorbent layer gives higher conversion efficiency (η) than uniform one. Structure with 0.11, 0.04, 0.01, and 2 μm thicknesses of MgF2, n-ZnO, n-CdS, and p-CIGS layers, respectively, gives the best performance. A graded doping of (3 × 1016-1022) cm−3 concentration in CIGS layer, 1022 cm−3 in ZnO layer, and 1021 cm−3 in CdS layer give a conversion efficiency of 29.43% in comparison to 22.92% of the proposed cell at room temperature.

The choice of Zn or ZnS layer in the stacked precursors for preparation of Cu2ZnSnS4 (CZTS) thin films

Cu2ZnSnS4 (CZTS) thin films are commonly used as an absorber layer in the thin film solar cell structure. In this study, CZTS thin films were produced by sulfurization of stacked precursor films that is prepared by deposition of Cu, Zn, SnS, ZnS films on glass substrate using sputtering method. The sequential sputter deposition was performed to obtain two distinct stacked precursors, Cu/SnS/Zn/Cu and Cu/SnS/ZnS/Cu respectively. Afterwards, annealing process was implemented at various reaction temperatures (500–575 °C) for 1 min utilizing rapid thermal processing (RTP). The EDX measurements revealed that all the prepared CZTS samples had Cu-poor and Zn-rich composition that are non-stoichiometric chemical composition. This non-stoichiometric composition is important for high efficient CZTS based solar cells. XRD measurements revealed that all patterns are dominated by diffraction planes of kesterite CZTS. The CuS, Cu2S and SnS2 secondary phases also were detected in the XRD pattern of some CZTS films. Raman spectroscopy measurements verified formation of kesterite CZTS phase for all films and picked out CTS phase for some samples prepared using Cu/SnS/Zn/Cu precursor films. The surface microstructure of the films that were obtained through SEM displayed polycrystalline surface structure. Room temperature PL emission spectra of the films showed broad peak at around 1.37–1.38 eV, which is near to the optical band gap of kesterite CZTS structure. Electrical characterization of the samples demonstrated that B-525 CZTS thin film has more suitable electrical resistivity and carrier concentration values for CZTS based solar cell applications.

Comparison of Light Trapping Limits Derived Using Various Methods for Thin Film GaAs Solar Cells.

The paper discusses and compares the Lambertian limits for light trapping (LT) in GaAs active layer based thin film solar cells as described by different mathematical theories and expressions. The Lambertian limits for thin film GaAs solar cell provide the maximum efficiency that can be achieved through LT structures and also indicate the advantage that these structure can provide for the design of GaAs thin film solar cell structure. The purpose to discuss difference Lambertian limit expressions is to understand and predict, which limiting benchmark value is more suited for nano LT structures based GaAs active material solar cells, considering GaAs material properties. The paper also compares these calculated limiting values with different nano LT structures including photonic crystal structures based designs proposed by the author. The aim is to check how much close a particular proposed structure is to the Lambertian values, so that we can predict that which is more suitable design to get best efficiency out of the single junction GaAs material based structure. The paper discussed the three Lambertian theories including that of Yablonovitch, Green and Schuster.

Enhancement of the performance of kesterite thin-film solar cells using dual absorber and ZnMgO buffer layers

A new structure of kesterite thin-film solar cells is simulated using SCAPS software. In addition, the structures of CZTS/ZnMgO, CZTSSe/CZTS/CdS and CZTSSe/CZTS/ZnMgO are suggested and scrutinized. In CZTS/ZnMgO structure, the efficiency, open-circuit voltage and short circuit current at the absorber layer thickness of 3 μm have been improved 35%, 15%, and 15% respectively. Furthermore, the efficiency of the proposed solar cell has been enhanced 60% by adding the CZTSSe absorber layer on the back of the CZTS layer. The optimum buffer layer thickness in the structures of CZTSSe/CZTS/CdS and CZTSSe/CZTS/ZnMgO are 150 nm and 125 nm, respectively. The simulation results show that the basic photovoltaic parameters (VOC, JSC, FF and η) have been decreased by variation of temperature from 300 K to 400 K. The optimal bandgap of the CZTSSe and ZnMgO in the structure of CZTSSe/CZTS/ZnMgO are obtained 0.9eV and 3.48eV, respectively in the ZnMgO optimal thickness of 50 nm. The highest efficiency of the kesterite solar cell with Zn0.81Mg0.19O buffer layer is 17.05%.

Elucidating the role of interfacial MoS2 layer in Cu2ZnSnS4 thin film solar cells by numerical analysis

In this study, the effects of transition metal dichalcogenide, MoS2 interfacial layer formation between the Cu2ZnSnS4 (CZTS) absorber layer and Mo back contact in a conventional CZTS thin film solar cell (TFSC) structure have been studied by numerical simulation using wxAMPS-1D software. The goal of this study is to elucidate the effects of both n and p-type MoS2 on the overall CZTS solar cell’s performance from the viewpoint of metal-semiconductor junction and heterojunction band alignment. Interestingly, CZTS device, regardless of p or n-type MoS2 largely outperforms device without any MoS2 due to lower back contact barrier value. Significant transition in efficiency is noticed when acceptor (increases efficiency) or donor (decreases efficiency) concentration has a transition from 1016 cm−3 to higher concentration of 1018 cm−3 or more. Also, effect of variable electron affinity and band gap of MoS2 has been discussed from band alignment perspective. Generally, MoS2 layer with lower electron affinity and band gap is preferred to induce desirable band alignment and subsequently result in higher efficiency. All-in all, the formation of p-type MoS2 in CZTS solar cells can be tuned to improve the cell performance mainly by doping with higher acceptor doping concentration and limiting layer thickness. However, the detrimental effect of n-MoS2 can be prevented by maintaining thinner layer in the vicinity of ∼30 nm with low to moderate donor doping (<1016 cm−3).

Increased Optical Absorption and Light–Matter Interaction in Silicon Thin-Film Solar Cell Nanostructure Using Graphene and 2-D Au/Ag Nanograting

Silicon solar cells with graphene have commonly some drawbacks in assuming Schottky junction configurations, small active areas, carrier’s recombination at interface of graphene/silicon junction, high cost, and complex manufacture processes. We report a new silicon thin-film solar cell structure with graphene, gold (Au) nanograting, and back silver (Ag) contact, which has advantages of simple fabrication method, no graphene/silicon Schottky junction complexity, high absorption, and high short circuit current density. We simulate the proposed specific graphene–silicon solar cell layer assembly by using the 2-D FEM under the standard global AM1.5 spectrum conditions. The generation of strong magnetic resonance field arises due to graphene sheet covered on top of gold nanograting and specific dielectric spacer thickness and slit period and leads to increase absorption and transport of charge carriers in p-i-n silicon layer sandwiched between dielectric spacer and back contact. We report that absorption improvement can be simply tuned by adjusting few geometric parameters of proposed device and maximum absorption is achieved up to 80% in near-infrared wavelength ranges. As an outcome, maximum short circuit current density ( $J_{\mathrm {sc}}$ ) of 32 mA/cm2, open-circuit voltage ( $V_{\mathrm {oc}}$ ) of 0.45 V, and calculated power conversion efficiency of 10.5% are achieved without chemical doping of graphene. The proposed simple structure configuration of silicon thin-film solar cell with graphene on top offers flexible tuneability, high short circuit current values, and increased optical absorption that are beneficial for practical fabrication and industrial applications.

Interdiffusion and Doping Gradients at the Buffer/Absorber Interface in Thin-Film Solar Cells.

An accurate determination of the net dopant concentration in photovoltaic absorbers is critical for understanding and optimizing solar cell performance. The complex device structure of multilayered thin-film solar cells poses challenges to determine the dopant concentration. Capacitance-voltage ( C- V) measurements of Cu(In,Ga)Se2 thin-film solar cells typically yield depth-dependent apparent doping profiles and are not consistent with Hall measurements of bare absorbers. We show that deep defects cannot fully explain these discrepancies. We instead find that the space charge region capacitance follows the model of a linearly graded junction in devices containing a CdS or Zn(O,S) buffer layer, indicating that elemental intermixing at the absorber/buffer interface alters the dopant concentration within the absorber. For absorbers covered with MgF2, C- V measurements indeed agree well with Hall measurements. Photoluminescence measurements of Cu(In,Ga)Se2 absorbers before and after deposition of a CdS layer provide further evidence for a significant reduction of the near-surface net dopant concentration in the presence of CdS. We thus demonstrate that interdiffusion at the absorber/buffer interface is a critical factor to consider in the correct interpretation of doping profiles obtained from C- V analysis in any multilayered solar cell and that the true bulk dopant concentration in thin-film devices might be considerably different.

Optical absorption spectra of Cu2ZnSn(S,Se)4 thin-film solar cells by Fourier transform photocurrent spectroscopy

We demonstrated the potential of Fourier transform photocurrent spectroscopy (FTPS) in investigating the optical absorption and quality of a Cu2ZnSn(S,Se)4 (CZTSSe) absorber within the cell structure. We fabricated thin-film solar cell structures with a CZTSSe absorber, which was prepared by a nanoparticle coating technique and a postannealing process. The optical absorption spectra of CZTSSe absorbers prepared at different annealing temperatures were measured by FTPS. We successfully evaluated the optical band-gap energy from the spectra. An exponential tail was found in the spectra. Urbach energy increased with increasing annealing temperature. The deterioration of photovoltaic performance with increasing Urbach energy might be due to potential fluctuation rather than to structural randomness.

Numerical simulations of perovskite thin-film solar cells using a CdS hole blocking layer

In this work, the numerical simulation of CH3NH3PbI3 perovskite solar cells was undertaken using the scaps-1d solar cell capacitance simulator software. A perovskite solar cell was simulated for best efficiency by replacing the traditional compact TiO2 layer with CdS (i.e., a hole-blocking layer) because CdS layers have been shown to possess a greater photostability than TiO2 with continuous illumination of sunlight. With the view of optimizing the device fabrication of perovskite/CdS thin-film solar cell (TFSC) for maximum efficiency, the perovskite/CdS TFSC structure was optimized theoretically using scaps-1d, which is possible because the perovskite layer has the same configuration and an excitation type as CdTe, copper-indium-gallium-selenide, and other inorganic semiconductor solar cells. Solar cell performance is highly dependent on the layer parameters, and so the effect that absorber thickness, bulk defects, and interface defects have on the device performance was studied and the device was optimized. Further, the effect that atmospheric conditions have on device performance was studied by varying the temperature and illumination density, and the optimum performance was found. After these optimizations, the simulation results show that a perovskite thickness of 500 nm yields an efficiency of 23.83% with a high open-circuit voltage of 1.37 V. These results for this absorber thickness is in good agreement with reports of experimental results for this device.

Enhanced external quantum efficiency from Cu2ZnSn(S,Se)4 solar cells prepared from nanoparticle inks

Cu2ZnSn(S,Se)4 (CZTSSe) thin film photovoltaic absorber layers are fabricated by selenizing Cu2ZnSnS4 (CZTS) nanoparticle thin films in a selenium rich atmosphere. The selenium vapor pressure is controlled to optimize the morphology and quality of the CZTSSe thin film. The largest grains are formed at the highest selenium vapor pressure of 226 mbar. Integrating this photovoltaic absorber layer in a conventional thin film solar cell structure yields a champion short circuit current of 37.9 mA/cm2 without an antireflection coating. This stems from an improved external quantum efficiency characteristic in the visible and near-infrared part of the solar spectrum. The physical basis of this improvement is qualitatively attributed to a substantial increase in the minority carrier diffusion length.