Thin Film Heterojunction Solar Cells Research Articles

Characteristics of a-SiC:H/a-SiGe:H hetero-junction thin film solar cells with and without a-Si:H buffer layer at the p/i interface

This article shows the characteristics on a - SiGe:H based solar cells with various structures. Based on these results, we proposed the a - SiC:H / a - SiGe:H hetero-junction thin film solar cells with a - Si:H buffer layer at the p/i interface to improve the performance of pin-type a - SiGe:H based solar cell. All films of amorphous materials were deposited by 13.56 MHz PECVD method. The effects of deposited parameters on the characteristics of a - SiC:H and a - SiGe:H films have been investigated by ultraviolet–visible–near infrared (UV–VIS–NIR) spectrophotometer. The various values of V oc , J sc , FF and η were measured under 100 mW/cm2 (AM 1.5) solar simulator irradiation. In the proposed structure, we achieved a higher conversion efficiency than general a - SiGe:H solar cell and a - SiC:H / a - SiGe:H hetero-junction thin film solar cells without a - Si:H buffer layer at the p/i interface. Based on results obtained from this study, we discuss the roles of a - Si:H buffer layer in a - SiC:H / a - SiGe:H hetero-junction thin film solar cells.

Synthesis of the wheat-like CdSe/CdTe thin film heterojunction and their photovoltaic applications

We report on the fabrication of wheat-like CdSe/CdTe thin film heterojunction solar cells made using a simple electrochemical deposition method and close-spaced sublimation technology on indium tin oxide (ITO) substrates. Structural, optical, and electrical properties of the wheat-like CdSe/CdTe thin film junctions were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), energy dispersive spectrometry (EDS), ultraviolet–visible (UV–vis) absorption spectrum and Keithley 2400 analysis. A significant red-shift of the absorption edge is observed in this heterojunction. The heterostructure is composed of the wheat-like CdSe array and CdTe thin film, showing optical properties typical of type II heterostructures that are suited for photovoltaic applications. A photocurrent density of 8.34 mA/cm2 has been obtained under visible light illumination of 100 mW/cm2. This study demonstrates that the electrochemical deposition and the close-spaced sublimation technology, which are easily adapted to other chemical systems, are promising techniques for large-scale fabrication of low-cost heterojunction solar cells.

Hole-conductor-free perovskite organic lead iodide heterojunction thin-film solar cells: High efficiency and junction property

Efficient hole-conductor-free organic lead iodide thin film solar cells have been fabricated with a sequential deposition method, and a highest efficiency of 10.49% has been achieved. Meanwhile, the ideal current-voltage model for a single heterojunction solar cell is applied to clarify the junction property of the cell. The model confirms that the TiO2/CH3NH3PbI3/Au cell is a typical heterojunction cell and the intrinsic parameters of the cell are comparable to that of the high-efficiency thin-film solar cells.

Investigations on Cu3SnS4 thin films prepared by spray pyrolysis

Thin films of Cu3SnS4, a promising absorber material for thin film heterojunction solar cells, are deposited using spray pyrolysis technique. The films are deposited at 360°C, 390°C and 420°C to study the effect of substrate temperature on the growth of these films. The thickness of the films is found to be ~0.6μm. Films deposited at 420°C are found to contain Cu3SnS4 as the dominant phase with CuS and Cu2SnS3 as the secondary phases. These films are annealed at 500°C and 550°C in sulfur atmosphere to improve the crystallinity and sulfur content in the films. With increase in the annealing temperature, the crystallinity is found to increase and the films annealed at 550°C are found to be near-stoichiometric, cubic Cu3SnS4. The crystallite size is evaluated to be ~40nm and the direct optical band gap of these films is found to be 1.75eV.

Nanopatterned Silicon Substrate Use in Heterojunction Thin Film Solar Cells Made by Magnetron Sputtering

This paper describes a method for fabricating silicon heterojunction thin film solar cells with an ITO/p-type a-Si : H/n-type c-Si structure by radiofrequency magnetron sputtering. A short-circuit current density and efficiency of 28.80 mA/cm2and 8.67% were achieved. Novel nanopatterned silicon wafers for use in cells are presented. Improved heterojunction cells are formed on a nanopatterned silicon substrate that is prepared with a self-assembled monolayer of SiO2nanospheres with a diameter of 550 nm used as an etching mask. The efficiency of the nanopattern silicon substrate heterojunction cells was 31.49% greater than that of heterojunction cells on a flat silicon wafer.

Sb2S3/SnSe thin film solar cells by thermal evaporation

ABSTRACTWe report a stable CdS/Sb2S3/SnSe heterojunction thin film solar cell deposited on SnO2:F (FTO) – coated glass substrates. Thermal evaporation at 10-5 Torr with substrate temperature of 400 °C was used to deposit Sb2S3 and SnSe thin films of 450 nm and 160 nm, respectively. Thin film Sb2S3 has an optical band gap (Eg) of 1.48 eV and photoconductivity (σp) of 4x10-7 Ω-1 cm-1 and thin film SnSe has an Eg of 1.28 eV and σp of 2 Ω-1 cm-1. The chemically deposited CdS thin film heated at 400 °C shows an Eg of 2.34 eV and σp of 0.1 Ω-1 cm-1. Stabilized solar cell structures with these thin films, FTO/CdS/Sb2S3/SnSe/C-Ag, showed open circuit voltage (Voc) of 0.60 V, short circuit current density (Jsc) of 5.51 mA/cm2 and power conversion efficiency (η) of 0.96% with a fill factor FF of 0.29. In the absence of the SnSe layer, Jsc decreases to 4.77 mA/cm2.

Band alignment of SnS/Zn(O,S) heterojunctions in SnS thin film solar cells

Band alignment is critical to the performance of heterojunction thin film solar cells. In this letter, we report band alignment studies of SnS/Zn(O,S) heterojunctions with various compositions of Zn(O,S). Valence band offsets (VBOs) are measured by femtosecond laser pump/probe ultraviolet photoelectron spectroscopy (fs-UPS) from which conduction band offsets (CBOs) are calculated by combining with band gaps obtained by optical transmission/reflection measurements. The SnS/Zn(O,S) heterojunctions with S/Zn ratios of 0.37 and 0.50 have desirable small positive CBOs, while a ratio of 0.64 produces an undesirable large positive CBO. The results are consistent with the device performance of SnS/Zn(O,S) solar cells.

Fabrication and Characterization of Rapidly Oxidized p-Type Cu2O Films from Cu Films and their Application to Heterojunction Thin-Film Solar Cells

In this study, we report that the metal Cu deposited on a glass substrate is formed into a stable p-type Cu2O film with excellent properties through rapid thermal oxidation (RTO). The pre-deposited Cu film layer went through thermal oxidation in the temperature range of 200–500 °C in O2 and air ambient, and the electrical and optical properties were intensively investigated. The optimized p-type Cu2O film heat-treated at a temperature of 200 °C in an air ambient has a carrier concentration of 1.25×1017 cm-3, mobility of 0.51 cm2 V-1 s-1, and resistivity of 9.86 Ω cm; its optical band gap reaches about 2.4 eV. Using the p-type Cu2O film with i- and n-type amorphous silicon layers, heterojunction thin-film solar cells were fabricated on glass substrates. These transparent solar cells employed Ga-doped ZnO films as top and bottom electrodes. Solar cells with Cu2O film oxidized at 200 °C in an air ambient have an open circuit voltage of 0.36 V, short-circuit current of 15.2 mA/cm2, and photoelectric conversion efficiency of 1.98%.

Growth of Polycrystalline In2S3 Thin Films by Chemical Bath Deposition Using Acetic Acid as a Complexing Agent for Solar Cell Application

In2S3 films have been successfully deposited on Corning glass substrates via chemical bath deposition (CBD) method using acetic acid as a novel complexing agent. The layers were grown by employing synthesis using indium sulphate and thioacetamide (TA) as precursors by varying TA concentration in the range of 0.1–0.5 M, keeping other deposition parameters constant. Energy dispersive X-ray analysis (EDAX) revealed an increase of S/In ratio in the films with the increase of TA concentration in the solution. The X-ray diffraction (XRD) analysis indicated a change in preferred orientation from (311) plane related to cubic structure to the (103) direction corresponding to the tetragonal crystal structure. The evaluated crystallite size varied in the range of 15–25 nm with the increase of TA concentration. Morphological analysis showed that the granular structure and the granular density decrease with the raise of TA concentration. The optical properties of the layers were also investigated using UV-Vis-NIR analysis, which indicated that all the In2S3 films had the optical transmittance >60% in the visible region, and the evaluated energy band varied in the range of 2.87–3.32 eV with the change of TA concentration. Further, a thin film heterojunction solar cell was fabricated using a novel absorber layer, SnS, with In2S3 as a buffer. The unoptimized SnS/In2S3/ZnO:Al solar cell showed a conversion efficiency of 0.6%.

Effect of annealing temperature on the properties of spray deposited Cu2 SnS3 thin films

Copper tin sulphide (Cu2SnS3), a promising solar cell absorber layer for thin film heterojunction solar cells, was grown onto soda-lime glass substrates by spray pyrolysis technique. The effect of annealing Cu2SnS3 (CTS) films in sulphur atmosphere at different annealing temperatures is investigated. From X-ray diffraction (XRD) and Raman spectra analysis, it is observed that the films exhibit polymorphism with tetragonal and monoclinic CTS phases. While the as-deposited films and the films annealed at 400 and 450 °C are found to contain tetragonal as well as monoclinic CTS phases, the films annealed at 500 °C are found to be mostly monoclinic CTS. The crystallite size is found to increase from 15 to 40 nm with increase of annealing temperature. From energy dispersive X-ray spectrometer (EDS) analysis, the films annealed at 400 and 450 °C are found to be near-stoichiometric Cu2SnS3. The direct optical band gap of CTS films with dominant tetragonal phase is found to be ∼1.10 eV, while that of films with dominant monoclinic phase is found to be 0.97 eV.

Electronic structure effect of polythiophene derivatives and nano N-Zn-Ag/TiO2 on performance of organic thin film solar cell

Nanocrystal N-Zn-Ag/TiO2 powders were prepared with N-Zn/TiO2 by photo deposition method. A series of pure polymers P3HT[poly(3-hexylthiophene)], P3OT[poly(3-octylthiophene)], P3DT[poly(3-decylthiophene)] and P3DDT[poly(3-dodecylthiophene)], was synthesized, which were used to synthesize p-n type semiconductor materials P3HT/N-Zn-Ag-TiO2, P3OT/N-Zn-Ag-TiO2, P3DT/N-Zn-Ag-TiO2 and P3DDT/N-Zn-Ag-TiO2 by in situ chemical method. X-Ray diffraction(XRD) and infrared(IR) spectroscopy showed the structure of the polymers and complexes. Ultraviolet-visible(UV-Vis) spectra and cyclic voltammograms(CV) showed the optical and electronic performance of the polymers and complexes. Two new single and double organic thin film heterojunction solar cells were prepared with the above mentioned synthesized powders as raw materials. Current-voltage(I–V) measurements indicate that the conversion efficiency of the single organic thin film heterojunction solar cell is higher than that of the double organic thin film heterojunction solar cells. Single organic thin film heterojunction solar cells based on P3DT/N-Zn-Ag-TiO2 can get a photoelectric conversion efficiency of 0.0408%. The performance of electronic transform between electron donor and acceptor on organic thin film solar cells was researched.

Characterization of Thermally Evaporated In2S3 Films for Solar Cell Application

Indium sulphide (In2S3) is one of the best alternatives for CdS as a buffer layer in CuInGaSe2-based thin film heterojunction solar cells. In this work, In2S3 films were prepared by thermal evaporation of In2S3 powder onto glass substrates at different temperatures that vary from 200°C to 300°C. The as-grown films were characterized using appropriate techniques to evaluate the chemical and physical properties. The X-ray diffraction analysis revealed that all the films were polycrystalline in nature with a strong (109) plane as the preferred orientation and consisted of tetragonal and cubic phases. The crystallite size and the lattice parameters are calculated. The scanning electron micrographs indicated smooth surface with fine grains. The optical analysis revealed a high optical transmittance for the layers with a direct optical band gap that varied in the range of 1.8–2.2 eV.

Growth and characterization of co-evaporated Cu2ZnSnS4 thin films

Thin films of Cu2ZnSnS4 (CZTS), a potential absorber layer for thin film heterojunction solar cells, have been successfully grown on soda-lime glass substrates held at 450 ∘C using co-evaporation technique. Cu, Sn, ZnS, and S, kept in molybdenum boats, are used as the source materials. The as-deposited films are annealed at 550 ∘C for an hour under sulphur atmosphere to improve the crystallinity and sulphur content. Films exhibited kesterite structure with (112) preferred orientation. The lattice parameters are found to be a = 0.544 nm and c = 1.098 nm. The crystallite size increased from 90 nm to 105 nm on annealing at 550 ∘C. Raman spectroscopy analysis of annealed films confirmed the CZTS phase formation with Cu2S as the secondary phase. The grain size is found to increase from 0.5 μm to 0.8 μm on annealing at 550 ∘C. The direct band gap of the annealed films is found to be 1.55 eV. The films are p-type in nature.

Simulation of a GaP/ Si Heterojunction Thin Film Solar Cell on Glass Substrate

This work presents a 1D simulation of light J-V characteristics of a GaP/ Si heterojunction thin film solar cell on glass substrate. The device is composed of a GaP/ Si n-p heterojunction, where the p-type Si layer serves as the absorber. A heavily doped p-type Si layer is used between the absorber and the substrate as a Back Surface Field (BSF) layer. The obtained results show slight improvement in shortcircuit current density (Jsc) and efficiency, compared to the present thin film poly-Si solar cells fabricated on glass substrate. At 1 sun, under AM1.5G, the open-circuit voltage (Voc) and the short-circuit current density (Jsc) were obtained as 0.5582 V and 28.42 mA/cm 2 , respectively. With a fill factor of 0.8274, the efficiency was calculated as 13.83%. Afterwards, a number of thin film cell designs were proposed, with corresponding simulation outcomes. Besides this, saturation in short-circuit current density (Jsc) and open-circuit voltage (Voc) with increasing absorber layer thickness was illustrated, in light of relevant simulation results.

Preparation and characterization of co-evaporated Cu2ZnGeSe4 thin films

Cu2ZnGeSe4 (CZGSe), a member of Cu2–II–IV–VI4 family, is a promising material for solar cell absorber layer in thin film heterojunction solar cells like Cu2ZnSnS4 and Cu2ZnSnSe4 which have been explored in recent years as alternate to CuInGaSe2 solar cells. The effect of substrate temperature (523K–723K) on the growth of CZGSe films is investigated by studying their structural, morphological and optical properties. Raman spectroscopy studies have been done to identify the phases in addition to X-ray diffraction studies. CZGSe films deposited at different substrate temperatures and annealed at 723K in selenium atmosphere are Cu-rich and Ge-poor and contained secondary phases Cu(2−x)Se and ZnSe. CZGSe films obtained by reducing the starting Cu mass by 10% were found to be single phase with stannite structure, the lattice parameters being a=0.563nm, c=1.101nm. The direct optical band gap of CZGSe films is found to be 1.63eV which is close to ideal band gap of 1.50eV for the highest photovoltaic conversion efficiency. The films are found to be p-type.

Nitrogen-doped cuprous oxide as a p-type hole-transporting layer in thin-film solar cells

We demonstrate the potential of a nitrogen-doped cuprous oxide (Cu2O:N) film as a p-type hole-transporting layer for photovoltaic devices. To reduce back-contact resistance and create an electron-reflecting back surface field, high carrier density and appropriate work function are desired for the layer. Its electrical and optical properties can be appropriately tuned via nitrogen-doping to create a semi-transparent tunnel junction to a back-contact. We fabricate Cu2O-based heterojunction thin-film solar cells and insert a 20 nm-thick Cu2O:N hole-transporting layer between a silver back-contact and a Cu2O light-absorbing layer. The insertion of a 20 nm-thick Cu2O:N layer results in sizeable enhancements of fill-factor and power conversion efficiency of the solar cells. Cu2O:N thin-films may also be useful in other photovoltaic material systems, improving their back-contact properties as well as widening the range of possible back-contact materials.

Characterization and Modeling of CdS/CdTe Heterojunction Thin-Film Solar Cell for High Efficiency Performance

Device simulation is used to investigate the current-voltage efficiency performance in CdTe/CdS photovoltaic solar cell. The role of several limiting factors such as back contact Schottky barrier and its relationship to the doping density and layer thickness is examined. The role of surface recombination velocity at back contact interface and extended CdTe layer is included. The base CdS/CdTe experimental device used in this study shows an efficiency of 16-17&#x25;. Simulation analysis is used to optimize the experimental base device under AM1.5 solar spectrum. Results obtained indicate that higher performance efficiency may be achieved by adding and optimizing an extended CdTe electron reflector layer at the back Schottky contact. In the optimization of the CdS/CdTe cell an extended electron reflector region with a barrier height of 0.1&#x2009;eV and a doping density of <svg style="vertical-align:-0.1638pt;width:54.1875px;" id="M1" height="16.049999" version="1.1" viewBox="0 0 54.1875 16.049999" width="54.1875" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(.017,-0,0,-.017,.062,15.775)"><path id="x37" d="M447 623l8 -12l-283 -613l-74 -10l-7 11q174 283 297 551h-216q-48 0 -62.5 -12t-33.5 -63h-29q10 60 18 148h382z" /></g><g transform="matrix(.017,-0,0,-.017,11.996,15.775)"><path id="xD7" d="M528 54l-36 -38l-198 201l-198 -201l-36 38l197 200l-197 201l36 38l198 -202l198 202l36 -38l-197 -201z" /></g><g transform="matrix(.017,-0,0,-.017,25.748,15.775)"><path id="x31" d="M384 0h-275v27q67 5 81.5 18.5t14.5 68.5v385q0 38 -7.5 47.5t-40.5 10.5l-48 2v24q85 15 178 52v-521q0 -55 14.5 -68.5t82.5 -18.5v-27z" /></g><g transform="matrix(.017,-0,0,-.017,33.907,15.775)"><path id="x30" d="M241 635q53 0 94 -28.5t63.5 -76t33.5 -102.5t11 -116q0 -58 -11 -112.5t-34 -103.5t-63.5 -78.5t-94.5 -29.5t-95 28t-64.5 75t-34.5 102.5t-11 118.5q0 58 11.5 112.5t34.5 103t64.5 78t95.5 29.5zM238 602q-32 0 -55.5 -25t-35.5 -68t-17.5 -91t-5.5 -105&#xA;q0 -76 10 -138.5t37 -107.5t69 -45q32 0 55.5 25t35.5 68.5t17.5 91.5t5.5 105t-5.5 105.5t-18 92t-36 68t-56.5 24.5z" /></g> <g transform="matrix(.012,-0,0,-.012,42.075,7.613)"><use xlink:href="#x31"/></g><g transform="matrix(.012,-0,0,-.012,47.786,7.613)"><path id="x38" d="M249 635q70 0 116 -43t46 -105q0 -46 -28 -80q-22 -25 -80 -64q62 -35 97 -75t35 -99q0 -81 -63 -131t-135 -50q-83 0 -137.5 45.5t-54.5 123.5q0 52 45 95q29 28 89 64q-109 62 -109 155q0 66 50.5 115t128.5 49zM238 603q-42 0 -67.5 -31t-25.5 -72q0 -50 32.5 -79.5&#xA;t98.5 -62.5q61 48 61 124q0 59 -29.5 90t-69.5 31zM248 20q46 0 76.5 33.5t30.5 89.5q0 50 -39 85.5t-110 71.5q-81 -54 -81 -137q0 -67 35.5 -105t87.5 -38z" /></g> </svg>&#x2009;cm<sup >&#x2212;3</sup> with an optimum thickness of 100&#x2009;nm results in best cell efficiency performance of 19.83&#x25; compared with the experimental data.

Fabrication and photovoltaic characteristics of Cu2O/TiO2 thin film heterojunction solar cell

A p-Cu2O/n-TiO2 thin film heterojunction solar cell has been fabricated by electrodeposition of Cu2O on radio-frequency sputtered n-TiO2 thin film. The heterojunction solar cell was characterized by X-ray diffraction, scanning electron microscopy and UV spectroscopy. Capacitance–voltage (C–V) and current–voltage measurements were performed. The values of barrier height and carrier concentration were estimated from the reverse bias C–V. The transport mechanism is related to space charge limited current and a trapped charge limited current having slope values of 1.95 and 3.5. Impedance measurement showed that electrical resistance decreases when the voltage is increased. The energy band diagram shows that the main-band discontinuity forms in the valence band. The ideality factor, barrier height and series resistance, fill factor and efficiency were also measured. The heterojunction solar cell exhibits a maximum fill factor and a power conversion efficiency of about 0.35 and 0.15% respectively.

Effect of annealing on conversion efficiency of nanostructured CdS/CuInSe2 heterojunction thin film solar cell prepared by chemical ion exchange route at room temperature

We report, the effect of air annealing on solar conversion efficiency of chemically grown nanostructured heterojunction thin films of CdS/CuInSe2, such 100, 200 and 300°C air annealed thin films characterized for physicochemical and optoelectronic properties. XRD pattern obtained from annealed thin films confirms tetragonal crystal geometry of CuInSe2 and an increase in average crystallite size from 16 to 32nm. An EDAX spectrum confirms expected and observed elemental composition in thin films. AFM represents high energy induced grain growth and agglomeration due to polygonization process. Increase in optical absorbance strength and decrease in energy band gap from 1.36 to 1.25eV is observed. Increase in charge carrier concentration from 2×1016 to 8×1017cm−3 is observed as calculated from Hall effect measurements and an enhancement in solar conversion efficiency from 0.26 to 0.47% is observed upon annealing.

Open-circuit analysis of thin film heterojunction solar cells

A new technique is proposed for the calculation of the width W of space charge region and consequently the concentration of uncompensated acceptors NA–ND, which is based on the open-circuit analysis of thin film heterojunction solar cells illuminated by monochromatic light with the wavelength within photosensitivity region. The proposed method was simulated under different values of the theoretically considered parameters (ideality coefficient n, saturation current I0 and shunt resistance Rsh) of a CdS/CdTe heterojunction solar cell. The calculated values of W and NA–ND were established to be dependent on the mentioned above electrical parameters.