Heterojunction Solar Cell Structure Research Articles

Designing and simulating of new highly efficient ultra-thin CIGS solar cell device structure: Plan to minimize cost per watt price

This research paper examines the execution of ultra-thin solar cells made from chalcopyrite copper indium gallium diselenide (CIGS). The study presents a new CIGS heterojunction solar cell structure, which includes a Cd-free tungsten disulfide (WS2) buffer layer and poly (3,4-ethylene dioxythiophene) polystyrene sulfonate (PEDOT: PSS) passivation layer. The performance of the solar cell is raised by a back surface field (BSF). A highly recombining rear surface is kept away from minority carriers by a field created by further strong doping at the back. The structure is Ni/PEDOT:PSS/CIGS/WS2/ZnO/Al and has been estimated numerically using the Opto-electrical stimulation of semiconductor layers simulator SCAPS-1D. A high efficiency with a Back surface passivated layer of 25.70 % with Voc of 0.81 V, Jsc of 39.33 mA/cm2, and FF of 79.89 % and without passivated layer efficiency of 17.58 % with Voc of 0.73 V, Jsc of 32.18 mA/cm2, and FF of 74.78 % is found for the intended CIGS-based solar cell with WS2 buffer. The interface between CIGS and WS2 forms a band structure that resembles spikes. This structure is crucial in enhancing the outputs by reducing carrier recombination. The optimal thicknesses for the buffer and CIGS absorber layers are 0.02 μm and 0.2 μm, respectively. These findings help reduce the cost per watt of the solar cell. Fabrication at a mass production scale, minimizing the thickness will have a significant impact on reducing cost.

Computational investigation towards highly efficient Sb2Se3 based solar cell with a thin WSe2 BSF layer

A novel structure of chalcogenide-based antimony selenide (Sb2Se3) which is the most promising absorber materials in the field of thin film solar cells with a tungsten diselenide (WSe2) back surface field (BSF) has been proposed in this paper. Antimony selenide (Sb2Se3) with a BSF has been observed by one-dimensional solar cell capacitance simulator (SCAPS-1D). Its recognizable properties make it one of the most usable for non-toxic solar cell absorbers. This paper demonstrated the planning and modeling of Al/FTO/n-TiO2/p-Sb2Se3/Ni (without BSF) and Al/FTO/n-TiO2/p-Sb2Se3/p+-WSe2/Ni (with BSF) structures. The capability of Al/FTO/n-TiO2/p-Sb2Se3/p+-WSe2/Ni heterojunction solar cell structure shows the promising performances. We have numerically simulated and observed the performance parameters such as power conversion efficiency (PCE), open circuit voltage (VOC), short circuit current density (JSC) and fill factor (FF) by tuning the different parameters such as thickness, doping concentration, defect density, the interface defect density, surface recombination velocity, series and shunt resistances along with temperature. The PCE of 20.61% with an absorber’s thickness of 800 nm for without BSF has been achieved. By inserting the WSe2 BSF with thickness of 100 nm, highly improving efficiency of 32.35% has been demonstrated. Our simulation and numerical analysis also provide valuable and important information that is very effective for further implementation and achieving high efficiency of thin film solar cell.

Mixed perovskite (MAPbI3-xClx) solar cells using light-emitting conjugated polymer DMP end-capped MDMO-PPV as a hole transport material

A series of solar cells (SCs) with methylammonium mixed halide perovskite active layers with a conjugated polymer (CP) poly[2-methoxy-5-(3,7-dimethyl-octyloxy)-1,4-phenylenevinylene] and end-capped with dimethylphenyl (MDMO-PPV) as a hole transport material (HTM) was fabricated under the same experimental settings, and the performance characteristics of the individual cells were compared. For comparison purposes, we fabricated a perovskite solar cell (PSC) with a lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI)-doped sprio-OMeTAD layer (LiTSO), which showed a power conversion efficiency (PCE) of 7.68 %. The layered solar cell with a structure of TiO2, perovskite and MDMO-PPV layers showed a PCE of 5.32 % and a fill factor of 0.478. The heterojunction solar cell (HJSC) made with a perovskite and MDMO-PPV mix showed a PCE of 5.68 %. The Field emission scanning electron microscope (FESEM) showed that in HJSC, the perovskite and CP were mixed well. However, they did not penetrate deeply into the TiO2 mesoporous layer, which would hinder electron transportation and thus cause efficiency loss. The HJSC structure was tested using different thicknesses of mesoporous TiO2 (m-TiO2). At an optimal m-TiO2 thickness, the blend of perovskite and MDMO-PPV infused up to 350 nm, thus improving the PCE to 7.438 % and retaining 91 % performance even after 4 weeks of continuous operation. The perovskite/conjugated polymer blend also formed a small SC above the m-TiO2 layer, showing complete penetration of the perovskite into the m-TiO2 layer. Additionally, the formation of a pure perovskite layer on top of the TiO2/perovskite and MDMO-PPV covers neatly on top of the perovskite layer and serves as a protective layer as well as a hole transport layer. An additional layer of LiTSO on top of the HJSC further improved the PCE to 7.76 %. The use of a CP as the hole transport layer reduces the dependency on separate materials and improves the device’s stability. It could also pave the way for an easy minimalistic method for integrated, flexible power electronics that contain solar cells (perovskite/conjugated polymer), organic light-emitting diodes, and supercapacitors made of graphene.

Simulating the performance of a highly efficient CuBi2O4-based thin-film solar cell

In this study, copper bismuth oxide (CuBi2O4) absorber-based thin film heterojunction solar cell structure consisting of Al/FTO/CdS/CuBi2O4/Ni has been proposed. The proposed solar cell device structure has been modeled and analyzed by using the solar cell capacitance simulator in one dimension (SCAPS-1D) software program. The performance of the proposed photovoltaic device is evaluated numerically by varying thickness, doping concentrations, defect density, operating temperature, back metal contact work function, series and shunt resistances. The current density–voltage behaviors at dark and under illumination are investigated. To realize the high efficiency CuBi2O4-based solar cell, the thickness, acceptor and donor densities, defect densities of different layers have been optimized. The present work reveals that the power conversion efficiency can be enhanced by increasing the absorber layer thickness. The efficiency of 26.0% with open-circuit voltage of 0.97 V, short-circuit current density of 31.61 mA/cm2, and fill-factor of 84.58% is achieved for the proposed solar cell at the optimum 2.0-μm-thick CuBi2O4 absorber layer. It is suggested that the p-type CuBi2O4 material proposed in the present study can be employed as a promising absorber layer for applications in the low cost and high efficiency thin-film solar cells.

Leakage current reduction in n-GaN/p-Si (100) heterojunction solar cells

We report on the growth of n-GaN/p-Si heterojunction solar cells via thermal chemical vapor deposition on Si (100) substrates at different growth temperatures (900, 950, and 1000 °C). The influence of growth temperature on the morphological, structural, optical, and electrical properties of GaN films has been elucidated. Increasing the growth temperature was found to reduce the internal stress and improve the material's crystallinity as confirmed via x-ray diffraction and Raman spectroscopy analyses. The photoluminescence spectra exhibit strong near band edge peaks in the range between 375 and 366 nm, with the peak intensity increasing with increasing the growth temperature. The current–voltage (J–V) characteristics of the assembled heterojunction solar cells showed the reverse leakage current to decrease with increasing the growth temperature. Consequently, the solar cell fabricated using the films grown at 1000 °C exhibits higher conversion efficiency (8.17%) than those grown at 950 °C (5.15%) and 900 °C (2.48%), respectively. This work shows that the structural, optical, and photovoltaic properties of the grown n-GaN/p-Si heterojunction solar cell structures are strongly influenced by the growth temperature.

Coupled modelling approach for optimization of bifacial silicon heterojunction solar cells with multi-scale interface textures.

For advanced optical analysis and optimization of solar cell structures with multi-scale interface textures, we applied a coupled modelling approach (CMA), where we couple the rigorous coupled wave analysis method with ray tracing and transfer matrix method. Coupling of the methods enables accurate optical analysis of solar cells made of thin coherent and thick incoherent layers and includes combinations of nano- and micro-scale textures at various positions in the structure. The approach is experimentally validated on standalone single- and both-side textured crystalline silicon wafers, as well as on complete silicon heterojunction (Si HJ) solar cell structures. Using CMA, fully encapsulated bifacial Si HJ solar cells are optically simulated first by applying single- and both-side illumination, and the effects of introducing nano inverted pyramids and random micro-pyramids at front and/or rear interfaces are analyzed. Secondly, an external light management foil with a three-sided pyramidal micro-texture is applied in simulations to the front and/or rear encapsulation glass, and the related improvements are quantified. For the optimal combination of internal textures in the analyzed structure (random micro-pyramids at the front and nano inverted pyramids at the back) and the use of the light management foil on both sides of the device, a 5.6% gain in the short-circuit current is predicted, compared to the reference case with no light management foil and with random micro-pyramids applied to the front and rear internal interfaces.

Radiation hardness investigation of heterojunction solar cell structures with TCO antireflection films

Phosphorus doped silicon carbide film as emitter in heterojunction structure was deposited on p-type Si(100) wafers at various deposition conditions by means of PECVD technology using silane (SiH4), methane (CH4), hydrogen (H2) and phosphine (PH3, 2 vol.% in H2) gas as precursors. ITO or IZO film was RF magnetron sputtered on top of the different P doped a-SiC:H(n) film. Irradiation of structures with Xe ions to total fluency 5×1011 cm−2 was performed at room temperature. Influence of phosphorus concentration and type of transparent conducting oxide was investigated. A deeper insight on the impact of irradiation on the electrophysical properties of sample was obtained by the analysis of complex impedance spectra.

Simulation of a Silicon Heterojunction Solar Cell with a Gradient Doping Emitter Layer

A silicon heterojunction solar cell structure consisting of a gradient doping emitter layer, which possesses a potential to obtain high power conversion efficiency, is explored by the numerical simulation tool automat for simulation of heterostructures. We have demonstrated that the gradient doping solar cell has a higher open-circuit voltage than a uniform doping solar cell, due to the introduction of an additional electric field, which can achieve a better conversion efficiency, whereas their thickness and defect state distribution are identical. A high conversion efficiency of 29.5% is achieved by using a gradient doping for the n-type emitter layer with the same reference as the uniform doping. In addition, through the investigation of the effect of gradient doping, we find that the field-effect passivation can appropriately explain the interesting behaviors that the recombination rate is less sensitive to the defect density state, and that the open-circuit voltage is enhanced when increasing the doping gradient in the n-a-Si emitter layer.

Molecular beam epitaxial growth of interdigitated quantum dots for heterojunction solar cells

Interdigitated quantum dots, which are multiple stacks of type-I InAs/GaAs quantum dots and type-II GaSb/GaAs quantum dots, are grown using molecular beam epitaxy. By incorporating the interdigitated quantum dots into a p-i-n AlGaAs/GaAs heterojunction solar cell structure, we demonstrate a photovoltaic effect with a 20.6% improvement in open-circuit voltage, when compared to that of another cell incorporating the same quantum dots but with a p-i-n GaAs homojunction architecture. A transmission electron microscopy is performed to analyze strain-induced defects created in the multi-stack quantum dot structures. The heterojunction solar cell incorporating the interdigitated quantum dots realized in this work would find potential applications in high-efficiency single-junction intermediate band solar cells operating under concentrated sunlight.

Fabrication and characterization of Cu/Cu2O/CuO/ZnO/Al–ZnO/Ag heterojunction solar cells

Glass/Cu/Cu2O/CuO/ZnO/Al–ZnO/Ag heterojunction solar cell structures have been successfully constructed by using a direct current magnetron sputtering technique. Photovoltaic (PV) solar cells fabricated as above indicated a conversion efficiency >5.6% and an open-circuit voltage (VOC) ∼0.57 V. Surface modification of CuO during ZnO deposition was identified as the limiting factor for obtaining higher performance heterojunction cells. Magnetron sputtering acted as a promising inexpensive and scalable technique for the fabrication of the above heterojunction for PV application. The diode quality factor for different cells fabricated here varied between 3.35 and 5.6 which were quite high (>2) compared to that for an ideal one. These are connected with mechanisms like interface recombination and tunneling enhanced interface recombination. Series resistance varied between 18.05 and 19.8 Ω cm2 while shunt resistance varied between 495 and 524 Ω cm2. The minority carrier life time ∼7 ms suggested lower recombination losses in our cells culminating in higher short circuit current density compared to copper oxide based cells fabricated by others.

Correlation of Band Electronic Structure to Efficiency in Perovskite Solar Cells with Vanadium Oxide Buffers

Over the past few years, solar cells with an organo metal halide perovskite structure have been well studied and attracted attention due to their excellent basic properties such as diffusion length of long charge carriers, good electrical properties, and light absorption coefficient, as well as easy and inexpensive solution processability. According to the efficiency chart, perovskite solar cells have achieved efficiencies of 22.1% in 2016 through rapid development with efficiency starting at 3.8%. However, despite these high efficiencies, one of the biggest problems of perovskite solar cells is the low stability and reliability of the devices in the atmosphere. For commercialization of perovskite solar cells, it is necessary to analyze and improve stability and efficiency. In the structure of the device, the electron transporting layer (ETL) and the hole transporting layer (HTL) transport charges, respectively, and mainly organic materials are used. The stability of the device can be enhanced by inserting a charge transporting layer of an inorganic material such as NiOx, ZnO, and VOx, which is superior in stability to organic materials such as PEDOT: PSS and Spiro-OMeTAD. Among them, p-type VOx with wide bandgap is used as HTL and can replace PEDOT: PSS. It is also important to note that in such a stacked heterojunction solar cell structure, band bending occurs due to different band gaps. Due to the non-optimization of conduction band offset (CBO) and valence band offset (VBO) at the interface between the absorption layer and the charge transport layer, it is possible to secure a smooth movement path of electrons and holes, and conversely, recombination of electrons and holes can be a cause of reduction in efficiency. Perovskite solar cells are also attracting attention as a strategy for improving efficiency at the interface between the charge transporting layer and the absorber layer. In this study, the efficiency difference and electronic structure analysis were carried out in planar heterojunction structure with ITO/VOx/Perovskite/PCBM/ZnO/Al structure fabricated by two process methods. The VOx buffer layer was deposited by vacuum deposition using RF magnetron sputtering and spin casting method. The VBM and core levels at the interface were measured using optical bandgap and depth profile x-ray photoelectron spectroscopy. After that, CBO and VBO values were derived from the calculations and the mechanism of electron and hole transport was clarified. As a result, it has been confirmed that the perovskite solar cell fabricated by the RF sputter process has an efficiency of about 13% and the device manufactured by the spin casting method has an efficiency of about 8%, and the reason for the difference efficiency is explained in relation to the electronic band structure.

Electric measurements of PV heterojunction structures a-SiC/c-Si

Abstract Due to the particular advantages of amorphous silicon or its alloys with carbon in comparison to conventional crystalline materials makes such a material still interesting for study. The amorphous silicon carbide may be used in a number of micro-mechanical and micro-electronics applications and also for photovoltaic energy conversion devices. Boron doped thin layers of amorphous silicon carbide, presented in this paper, were prepared due to the optimization process for preparation of heterojunction solar cell structure. DC and AC measurement and subsequent evaluation were carried out in order to comprehensively assess the electrical transport processes in the prepared a-SiC/c-Si structures. We have investigated the influence of methane content in deposition gas mixture and different electrode configuration.

N-GaP/p-Si heterojunction solar cells fabricated by PE-ALD

Significant progress in photovoltaic conversion of solar energy can be achieved by new technological approaches that will improve the efficiency of solar cells and make them appropriate for mass production. A new technological approach for the growth of III-V compounds on Si substrates using low temperature plasma-enhanced atomic layer deposition (PE-ALD) is explored in the paper. This technique, which consists of alternatively changing the phosphorus and gallium atom source flows providing the growth of one monolayer by cycle, was developed for the growth of GaP films on Si substrates in a standard PECVD setup at 380 °C using PH3 and TMG (Trimethylgallium) as sources of III and V atoms. First (n)GaP/(p)c-Si anisotype heterojunction solar cell structures fabricated by PE-ALD exhibit open circuit voltage values similar to that obtained for (n)a-Si:H/(p)c-Si heterojunctions fabricated using the same (p)c-Si substrates. However (n)GaP/(p)c-Si solar cells demonstrates a potential to extend a high quantum efficiency in the short wavelength region due to lower absorption losses in the GaP emitter layer.

Making Heterojunction Solar Cell Structure with Two Doner Polymer Materials and the Effect of Annealing Temperature

Making Heterojunction Solar Cell Structure with Two Doner Polymer Materials and the Effect of Annealing Temperature

High-efficiency thin film ZnMgO/ZnO solar cell simulation approach: Temperature dependency, BSF and efficient small signal analysis

Small signal analysis for Al/ZnO/c-Si/Ag heterojunction solar cell structure is investigated in this simulation work. Effect of signal frequency, device temperature and junction interface defect state density on the junction diffusion capacitance and device conductance are thoroughly examined. Built in potential measurement highlights variation from 0.8 to 2.1 eV for the range100 Hz to 8 MHz which showing a good agreement with the practical value. Low temperature (10–100 K) conductance measurement at 2 V biasing results a localised Fermi level state density 9.54 × 1040 cm−3eV−1and evidences variable range hopping conduction. Excellent improvement of short circuit current density and efficiency is observed using MgxZn1-xO window layer. The increase in short circuit current density and efficiency due to the use of the window layer are 31.85 mA cm−2 and 19.17% respectively. For all the study illumination of 400 nm monochromatic light with photon flux 2.8 × 1017 cm−2s−1 and spectral width 10 nm are applied. Uses of 400 nm light is due to study of temperature dependency on open circuit voltage of solar cell. Using 1000 wt/m2 the efficiency of solar cell is enhanced from 19.88% to 23.15%.

High-performance ultraviolet-visible tunable perovskite photodetector based on solar cell structure

An ultraviolet (UV)-visible tunable photodetector based on ZnO nanorod arrays (NAs)/perovskite heterojunction solar cell structures is presented, in which the ZnO NAs are prepared using the hydrothermal method and annealed in different atmospheres. Based on solar cell structure perovskite photodetectors, it exhibited highly repeatable and stable photoelectric response characteristics. In addition, the devices with ZnO NAs annealed in a vacuum showed a high responsivity of about 1014 cm Hz1/2 W−1 in the visible region, whereas the devices with ZnO NAs annealed in air exhibited good detectivity in the UV region, especially at around 350 nm. Furthermore, when the annealing atmosphere of the ZnO nanorods was changed from vacuum to air, the dominant detection region of the photodetectors was altered from the visible to the ultraviolet region. These results enable potential applications of the ZnO NAs/perovskite photodetectors in ultraviolet and visible regions.

PbS/CdS heterojunction quantum dot solar cells

The present work investigates the effects of combination of lead sulfide PbS quantum dots and cadmium sulfide CdS nanoparticles (NPs), with n-type and p-type semiconductors, on the photovoltaic performance of heterojunction solar cells. Namely, p-type semiconductors are: poly[3,4-ethylenedioxythiophene]–poly[styrenesulfonate] (PEDOT:PSS), copper oxide (CuO) NPs and graphene oxide (GO); while n-type semiconductors are: zinc oxide (ZnO) NPs and titanium dioxide (TiO2) NPs. The above were used to fabricate heterojunction solar cell structures via spin coating, chemical bath deposition and SILAR cycle methods. The morphology and energy band diagram for each solar cell were examined. The photovoltaic performance of the cells was measured under 1 sun illumination (irradiation of 100 mW/cm2). This efficiency ranged between 0.388 and 5.04 %. The solar cell with FTO/ZnO/TiO2/CdS/PbS/PEDOT:PSS/Au structure and optimum layers’ thickness exhibited a short-circuit current of 24.2 mA/cm2, open circuit voltage of 544 mV, a fill factor of 38.2 % and a power conversion efficiency of 5.04 % with reliably good stability. This is related to the uniform surface morphology throughout every cell layer without voids, pinholes or cracks. Furthermore, gradual band energy levels alignment of n-type and p-type NPs (CdS/PbS), as well as high hole mobility of PEDOT:PSS and the high electron affinity of ZnO and TiO2 are other major factors that controls quantum efficiency.

Electrical and Capacitance Diagnostic Techniques as a Support for the Development of Silicon Heterojunction Solar Cells

Abstract In this paper we present the utilization of capacitance and current-voltage diagnostic techniques to analyse silicon heterojunction solar cell structures properties, particularly focused on the inspection of the amorphous emitter and amorphous silicon/crystalline silicon hetero-interface. The capacitance characterization of investigated samples have revealed the need for improvement of the a-Si:H/c-Si heterointerface quality as a main direction to obtain superior output performance of heterojunction cells. In addition, current-voltage characterization emphasized importance for enhancement of the light management in the structure. The obtained results demonstrate that electrical and capacitance diagnostic techniques can represents important diagnostic tools in the process of optimization of solar cells.

Self-assembled monolayer modified ITO in P3HT:PC61BM organic solar cells with improved efficiency

In this paper we demonstrate the use of self-assembled monolayer modified indium tin oxide (ITO) electrode in bulk heterojunction solar cell structure based on a photoactive layer of poly(3-hexylthiophene) and [6,6]-phenyl C61 butyric acid methyl ester (P3HT:PC61BM). The device studies show that there is a significant enhancement in the short-circuit current as well as in the shunt resistance on use of the hexamethyldisilazane (HMDS) layer. The enhancement in short-circuit current density is attributed to the good contact formed between the organic materials and the methyl groups of HMDS. A significant improvement in the external quantum efficiency is also observed in case of the HMDS modified ITO based solar cells.

Investigation of CdS and CdTe thin films and influence of CdCl2 on CdTe/CdS structure

CdTe/CdS heterojunction solar cell structure has been fabricated using simple, easy and low-cost methods. To fabricate this structure, CdS and CdTe thin films are deposited onto FTO-coated conducting glass substrates by chemical bath deposition (CBD) and electrodeposition method, respectively. The optimized growth conditions are chosen for both CdS and CdTe films by investigating the optical, structural and morphological properties of both the as-deposited and annealed films. Optical measurement showed that CdS films have higher transmittance and lower absorbance, and CdTe films have lower transmittance and higher absorbance in the near infrared region. The band gap of CdS films is estimated to lie in the range 2.29–2.41eV and that of CdTe films is in the range 1.53–1.55eV. X-ray diffraction (XRD) study reveals that CdS and CdTe films are polycrystalline with preferential orientation of (111) plane. Scanning electron microscopy (SEM) study reveals that both films are smooth, void-free and uniformly distributed over the surface of the substrate. Fabricated CdTe/CdS structure showed the anticipated rectifying behaviour, and the rectifying behaviour is observed to improve due to CdCl2 treatment.