Homojunction Solar Cells Research Articles

Efficiency of Heterojunction Solar Cells Based on Optical Band Gap

Electric energy production by fuel burning produces dangerous pollutants. The photovoltaic solar cell is a suitable alternative. For thin film solar cells, efficiency improvement should be carried out through continued development of their characteristics. The homojunction solar cell has reached its optimum. In the present work, a relationship between optical band gap and solar cell efficiency of heterojunctions has been established. Suitable band gaps of a pair of heterojunctions are required to get maximum efficiency for an appropriate frequency of solar radiation. The efficiency of a couple of extrinsic semiconductors can be calculated theoretically. An optimum band gap of a pair of heterojunctions with the highest efficiency may be found by this process. The efficiency of a few heterojunctions has been calculated using reported data. The results show that efficiency is increased with optical band gaps, and type-I is more efficient than type-II heterojunctions. The work may help to improve the solar cell efficiency.

Cu2O Homojunction Solar Cells: Efficiency Enhancement with a High Short Circuit Current

Cu2O Homojunction Solar Cells: Efficiency Enhancement with a High Short Circuit Current

An experimental investigation of spin-on doping optimization for enhanced electrical characteristics in silicon homojunction solar cells: Proof of concept

The pursuit of enhancing the performance of silicon-based solar cells is pivotal for the progression of solar photovoltaics as the most potential renewable energy technologies. Despite the existence of sophisticated methods like diffusion and ion implantation for doping phosphorus into p-type silicon wafers in the semiconductor industry, there is a compelling need to research spin-on doping techniques, especially in the context of tandem devices, where fabricating the bottom cell demands meticulous control over conditions. The primary challenge with existing silicon cell fabrication methods lies in their complexity, cost, and environmental concerns. Thus, this research focuses on the optimization of parameters, such as, deposition of the spin on doping layer, emitter thickness (Xj), and dopant concentration (ND) to maximize solar cell efficiency. We utilized both fabrication and simulation techniques to delve into these factors. Employing silicon wafer thickness of 625 μm, the study explored the effects of altering the count of dopant layers through the spin-on dopant (SOD) technique in the device fabrication. Interestingly, the increase of the dopant layers from 1 to 4 enhances efficiency, whereby, further addition of 6 and 8 layers worsens both series and shunt resistances, affecting the solar cell performance. The peak efficiency of 11.75 % achieved in fabrication of 4 layers dopant. By using device simulation with wxAMPS to perform a combinatorial analysis of Xj and ND, we further identified the optimal conditions for an emitter to achieve peak performance. Altering Xj between 0.05 μm and 10 μm and adjusting ND from 1e+15 cm−3 to 9e+15 cm−3, we found that maximum efficiency of 14.18 % was attained for Xj = 1 μm and ND = 9e+15 cm−3. This research addresses a crucial knowledge gap, providing insights for creating more efficient, cost-effective, and flexible silicon solar cells, thereby enhancing their viability as a sustainable energy source.

Temperature-dependent electronic, optical, and solar cell device properties of AlAs and AlSb semiconductors and their p-n homojunctions

AlSb and AlAs have attracted renewed interest in recent years as promising photovoltaic (PV) materials due to significant light absorption, eco-friendliness, and low cost. Here, density functional theory (DFT) in combination with the non-equilibrium Green's function method (NEGF) has been used to compute the temperature-dependent PV parameters of nanoscale AlSb and AlAs p-n junction solar cell devices. In particular, the influence of electron-phonon coupling (EPC) and spin-orbit coupling (SOC) on the PV properties of these devices is investigated. Our results highlight the importance of inclusion of EPC in evaluating the ab initio PV properties of p-n junctions at finite temperatures. At non-zero temperatures, the PV parameters can differ significantly compared to those at zero temperature due to phonon-assisted tunnelling of charge carriers across the p-n junction. In particular, the mobility of low-effective-mass carriers at the p-n junction is found to be enhanced by phonon scattering, which in turn results in improved PV transport properties. The short-circuit current (Jsc) at 300 K proved to be 21.7% (16.2%) higher for AlSb (AlAs) than that at 0 K. On the other hand, the open-circuit voltage (Voc) at 300 K proved to be 19.1% (16.7%) lower for AlSb (AlAs) than that at 0 K. Jsc is higher in AlSb than in AlAs due to higher phonon-influenced mobility of low-effective-mass carriers. Overall, our study strongly suggests the importance of inclusion of EPC and hence phonon scattering in the first-principles quantitative determination of PV parameters of solar cells. The estimates obtained in this study may be utilized as input ab initio parameters in continuum-model-based multi-scale simulations of AlSb and AlAs p-n homo-junction solar cells.

Performance assessment of an eco-friendly tandem solar cell based on double perovskite Cs2AgBiBr6

Tandem solar cells have a wider photon absorption range, allowing them to provide better efficiency than single-junction SC. The upper cell absorbs high-energy photons, while the lower cell absorbs low-energy filtered photons. However, in order to obtain affordable, efficient, and long-lasting SC, the absorber layers of the top and bottom cells must be integrated with an adequate bandgap. This research suggests tandem perovskite solar cells as upper band active materials in this setting. The Si homojunction solar cell's performance was improved by investigating the thicknesses of the p−type and n−type layers, doping concentrations, and defect densities. The thickness variation of the perovskite solar cell (100−400nm) is then optimized. To precisely replicate the tandem devices, the estimated spectra of the perovskite SC are optically filtered onto the lower cells. Current matching was achieved by adjusting the thickness of the perovskite sub-cell with different bottom layer thicknesses, and the optimized efficiency of 36.26% for the perovskite/Si tandem device was shown. The discoveries will open the door for the upcoming creation of high−efficiency, low-energy solar cells.

A review of Cu2O solar cell

Cu2O-based solar cells offer a promising solution to address future energy challenges due to their affordability, eco-friendliness, and impressive power conversion efficiency (PCE). With the development of thin film deposition technology, the maximum PCE of single-junction solar cells fabricated based on Cu2O is 9.5%. Because the spectral sensitivity overlaps between Cu2O and crystalline silicon (c-Si) is small, Cu2O thin-film solar cells can be made into tandem solar cells with Si-based solar cells to achieve higher PCE. The Cu2O–Si tandem solar cell has been delivered 24.2% PCE in 2020, a time when the PCE of stand-alone silicon solar cells was 17.6%. The purpose of this paper is to summarize the development of Cu2O-based heterojunction, homojunction. The Cu2O material properties, n and p-type doping, the role of defects and impurities in bulk of films or at the interface of the p–n-junction and n-type buffer layer on the performance of Cu2O-based heterojunction like ZnO–Cu2O, and the difficulty in decreasing the interface state and doping in Cu2O homojunction solar cells are discussed. This review discusses the Cu2O film material preparation method, the history of Cu2O based solar cells, the essential factors required to enhance the performance of various types of Cu2O-based solar cells, and the potential future research opportunities for as a top subcells in Cu2O–Si tandem solar cells.

Improvement of InGaP solar cells grown with TBP in planetary MOVPE reactor

In this study, the impact of various growth parameters, such as wafer temperature, device structures, and substrate misorientation, on the quality of InGaP epitaxial layers and solar cells grown in a planetary MOVPE reactor using TBP as a P source were investigated and optimized. Results showed that the carrier lifetime in unintentionally n-doped InGaP significantly decreased as the growth temperature increased from 560 to 590 °C. At temperatures above 600 °C, the growth of InGaP was unsuccessful due to extremely rough surface morphology. The study revealed that InGaP rear homojunction and rear heterojunction solar cells using n-type InGaP base layers displayed improved photo-carrier collection and performance compared to traditional front junction solar cells with p-type InGaP base layers. Notably, InGaP grown on GaAs (001) with a 5° miscut towards (111)A was found to have better quality, while InGaP grown on GaAs (001) with a 6° tilt towards (111)B had worse results in terms of carrier lifetime, PL intensity, and solar cell performance.

Comprehensive device simulation of barium silicide solar cells with diverse ETMs and HTMs

The photovoltaic performances of n-i-p or inverted p-i-n BaSi2 homojunction solar cells are limited by the parasitic high light absorption of n-BaSi2 or p-BaSi2 window layer. In this work, diverse electron transport materials (ETMs) and hole transport materials (HTMs) are employed instead of BaSi2 as window layers to promote the performances of BaSi2 solar cells, and the effects of different ETMs and HTMs were simulated and comprehensively studied. For n-ETM/i-BaSi2/p-BaSi2 solar cells, the solar cell with ZnO exhibits the highest efficiency of 28.21%. As increasing the thicknesses of ETM layer from 5[Formula: see text]nm to 100[Formula: see text]nm, the efficiency for n-BaSi2/i-BaSi2/p-BaSi2 solar cell decreases seriously from 24.52% to 15.99%, while the solar cells with wide band gap ETMs including SnO2, TiO2 and ZnO show neglectable change in performances. The performances n-ETM/i-BaSi2/p-BaSi2 solar cells are affected by donor like defects more than acceptor like defects in i-BaSi2. For p-HTM/i-BaSi2/n-BaSi2 solar cells, employing Cu2O, CuI, CuSCN or NiO as HTM layer produces evident valence band discrepancies at HTM/i-BaSi2 interfaces. Heavy doping in HTM layer is necessary desired to overcome the energy band barriers. As increasing the thicknesses of HTM layer from 5 nm to 100 nm, the efficiency for p-BaSi2/i-BaSi2/n-BaSi2 solar cell also decreases from 24.52% to 15.99%, while the solar cells with wide band gap HTMs including CuI, CuSCN and NiO show neglectable change, and the efficiency for p-Cu2O/i-BaSi2/n-BaSi2 solar cells decreases slightly from 25.86% to 24.88%. The performances of p-HTM/i-BaSi2/n-BaSi2 solar cells are affected by acceptor like defects more than donor like defects in i-BaSi2.

Design and Performance Enhancement of a GaAs-Based Homojunction Solar Cell Using Ga0.5In0.5P as a Back Surface Field (BSF): A Simulation Approach

The GaAs semiconductor is a solar energy promising material for photovoltaic applications due to its good optical and electronic properties. In this work, a homojunction GaAs solar cell with AlxGa1-xAs and GayIn1-yP solar energy materials as window and back surface field (BSF) layers, respectively, was simulated and investigated using SCAPS-1D software. The performance of the GaAs-based solar cell is evaluated for different proportions ofxandy, which allowed us to obtain the values of 0.8 and 0.5 forxandy, respectively, as the best values for high performance. We then continued the optimization by taking into account some parameters of the solar cell, such as thickness, doping, and bulk defect density of the p-GaAs base, n-GaAs emitter, and Ga0.5In0.5P BSF layer. Solar cell efficiency increases with emitter thickness, but the recombination phenomenon is more pronounced than that of electron-hole pair generation in the case of a thicker base. The effect of variation in the work function of the back contact has also been studied, and the best performance is for a platinum (Pt) electrode. The optimized GaAs-based solar cell achieves a power conversion efficiency of 35.44% (JSC=31.52 mA/cm2,VOC=1.26 V,FF=89.14%) and a temperature coefficient of -0.036%/°C. These simulation results provide insight into the various ways to improve the efficiency of GaAs-based solar cells.

Comprehensive Review on Thin Film Homojunction Solar Cells: Technologies, Progress and Challenges

With the aim of achieving high efficiency, cost-effectiveness, and reliability of solar cells, several technologies have been studied. Recently, emerging materials have appeared to replace Si-based cells, seeking economic fabrication of solar cells. Thin-film solar cells (TFSCs) are considered strong candidates for this mission, specifically perovskite-based solar cells, reporting competitive power convergence efficiencies reaching up to 25.7%. Substantial efforts have been invested in experimental and research work to surpass the Si-based cells performance. Simulation analysis is a major tool in achieving this target by detecting design problems and providing possible solutions. Usually, a TFSC adopts p-i-n heterojunction architecture by employing carrier transport materials along with the absorber material in order to extract the photogenerated electrons and holes by realizing a built-in electric field. Eventually, this dependency of conventional heterojunction TFSCs on carrier transport layers results in cost-ineffective cells and increases the possibility of device instability and interface problems. Thus, the design of p-n homojunction TFSCs is highly desirable as an essential direction of structural innovation to realize efficient solar cell operation. In this review, a summary of the fundamentals of TFSC materials, recent design and technology progress, and methodologies for improving the device performance using experimental research studies will be discussed. Further, simulation analysis will be provided by demonstrating the latest research work outcomes, highlighting the major achievements and the most common challenges facing thin film homojunction solar cell structures and the methods to improve them.

Br-doped n-type SnS single crystals with carrier concentrations suitable for homojunction solar cells

SnS has attracted considerable attention as a semiconductor material for use in thin-film solar cells. In particular, fabricating a SnS homojunction is essential for achieving highly efficient solar cells. However, controlling the n-type SnS carrier concentration to the optimum level of 1015–1016 cm−3 is currently challenging. Herein, we report a doping strategy for n-type SnS and the fabrication of n-type single crystals with a carrier concentration of ∼1016 cm−3 using Br as the dopant. Br-doped single crystals were grown using SnBr2 as the flux, while Cl-doped single crystals were grown as a reference using the same method. Cl-doped SnS exhibited a carrier concentration of ∼1018 cm−3, whereas Br-doped SnS realized a concentration of 3.2 × 1016 cm−3. The Br-doped crystals exhibited thermal-activation-type behavior based on the temperature dependence of the carrier concentration, with an activation energy of 52 meV determined. X-ray photoelectron spectroscopy revealed that Br- and Cl-doped SnS exhibit Fermi levels at 0.22 and 0.15 eV relative to the bottom of the conduction band, respectively. Furthermore, the measured electrical and electronic properties suggested that Br-doped SnS has a lower Fermi level than Cl-doped SnS. These results indicate that Br-doped SnS is suitable for forming n-layers in SnS homojunction solar cells.

Structural design of BaSi2 solar cells with a-SiC electron-selective transport layers

Sputter-deposited polycrystalline BaSi2 films capped with a 5 nm thick a-SiC layer showed high photoresponsivity. This means that the a-SiC layer functions as a capping layer to prevent surface oxidation of BaSi2. Based on the measured absorption edge, the electron affinity of the a-SiC layer, and the work function of the TiN layer, the a-SiC is considered to act as an electron transport layer (ETL) for the BaSi2 light absorber layer/a-SiC interlayer/TiN contact structure in a BaSi2 solar cell. Using a 10 nm thick p+-BaSi2 layer as a hole transport layer, we investigated the effect of the BaSi2/a-SiC layered structure on the device performance of a BaSi2-pn homojunction solar cell by a one-dimensional device simulator (AFORS-HET v2.5). The a-SiC ETL effectively separates photogenerated carriers and allows transport of electrons while blocking holes to achieve an efficiency of 22% for a 500 nm thick BaSi2 light absorber layer.

The effect of fluorination on the low and high frequency dielectric constants of non-polymeric organic semiconductors – towards homojunction solar cells

Fluorination of a non-polymeric donor–acceptor–acceptor–donor organic semiconductor leads to an increase in the thin-film low frequency and decrease in the optical frequency dielectric constant relative to the protonated material.

Photovoltaic properties of new solar cell based on ideal cubic NaNbO3 thin films: a combined experimental and density functional theory study.

We explore the photovoltaic properties of a novel homojunction solar cell based on NNO(p)/NNO(n) perovskite by employing a combination of material synthesis, characterization and density functional theory calculations that are novel ideas compared to those previously reported in the literature. The band structure reveals that NaNbO3 introduces a n-type semiconductor. Moreover, using DFT calculation, we created n-NNO by a simple substitution in the O site by 4.16% fluorine atoms. Experimental and DFT calculation reveals that NNO perovskite exhibits a direct bandgap of ∼1.6 eV, with a slightly larger two other direct bandgaps of ∼2.13 and 3.24 eV. After extracting the necessary parameters, an electrical modelization of an n-NNO/p-NNO solar cell is performed by Maple software revealed that the cell conversion efficiency can reach 17% which presents a first path to identify a new solar cell based only on perovskite material.

High broadband light absorption in ultrathin MoS2 homojunction solar cells.

Transition metal dichalcogenides (TMDCs) have been proposed as light absorber materials for ultrathin solar cells. These materials are characterized by their strong light-matter interaction and the possibility to be assembled into devices at room temperature. Here, we model the optical absorptance of an ultrathin MoS2 absorber embedded in different designs of a 1D optical cavity. We find that up to 87% of the photons contained in the 300-700 nm range of the AM1.5G spectrum can be absorbed employing MoS2 absorbers as thin as 10 nm sandwiched between a h-BN top layer and an optically thick Ag reflector. An h-BN/MoS2/h-BN/Ag cavity produces 0.89 average absorptance for a 57-nm-thick MoS2 slab and it also maximizes the absorption of extremely thin absorbers, between 1 and 9 nm. We also model a possible large-scale device on a glass substrate combined with indium-tin oxide (ITO) whose absorptance is comparable to the other presented structures. The high broadband absorption in these light-trapping structures is caused by the amplification of the zeroth Fabry-Perot interference mode. This study demonstrates that light absorption in ultrathin solar cells based on nanometric TMDC absorbers can compete with conventional photovoltaic technology and provides different simple optical designs to choose from depending on the electronic characteristics of the TMDC junction.

Photovoltaic parameter extraction and optimisation of ZnO/GO based hybrid solar trigeneration system using SCAPS 1D

In this work, simulative investigation of Zinc Oxide/Graphene Oxide based novel hybrid solar trigeneration system has been performed to identify its photovoltaic parameters i.e. Current density (Jsc), Open circuit voltage (Voc), fill factor (FF), Power Conversion Efficiency (PCE), using SCAPS 1D (Solar Cell Capacitance Simulator) software. A comparison was made between the simulated and estimated experimental values for the cell under standard test conditions, which showed an all over good agreement. The simulated values of VOC, JSC, FF, PCE for ZnO/GO are 0.79 V, 12.46 mA/cm2, 52.14 %, 8.46 % respectively. The extracted experimental values are 0.72 V, 7.24 mA/cm2, 56.94 %, 9.12 % respectively. Further analysis is done to study the effect of graphene oxide layer thickness on PV properties of the cell. Also performance of ZnO/GO cell was compared to ZnO/SiO2 cell and it was found that the efficiency of the two is nearly similar when evaluated at 32 °C under 1 Sun and AM 1.5. A limiting factor in using the high-efficiency Si homojunction solar cell is its high fabrication cost. Hence here we try to replace GO with SiO2 because of its simpler synthesis and involved fabrication processes. But the only backdrop is its lower efficiency, which can be improved by rigorous simulation analysis of the organic semiconductor layer. The performance of the presented hybrid system has been estimated and differentiated with other known solar trigeneration system to evaluate the viability of the showcased model, provided physical constraints imposed by the environment are considered depending upon the system installation location.

Analysis and design of p-n homojunction Sb2Se3 solar cells by numerical simulation

Antimony selenide (Sb2Se3) is considered a promising candidate utilized as an absorber in thin film solar cell (TFSC) technology thanks to its non-toxic and earth-abundant nature besides its reported high absorption coefficient. To enhance the power conversion efficiency (PCE) of Sb2Se3 solar cells, we report some design suggestions by applying device simulation. The numerical model is firstly validated by calibration of simulation results vs those from an experimental Sb2Se3 solar cell structure composed of FTO/CdS/Sb2Se3/Au where CdS serves as an electron transport layer (ETL). Then, the cell is modified to include an embedded p-n homojunction. In contrast to the conventional heterostructure design, a homojunction structure has crucial benefits in terms of both electronic and optoelectronic characteristics such as the extra produced built-in electric field which can increase the transport of photogenerated carriers. Three device configurations are presented and compared. The first and the second cases are when using CdS and ZnOS as ETLs. Utilizing ZnOS ternary compound is found to be more beneficial as its conduction band offset with the absorber layer could be tuned to attain a proper cliff-like band alignment. The third case is when considering homojunction design free from all carrier transport layers. Possible paths for device optimization are investigated to boost the efficiency in a try to overcome the efficiency bottleneck encountered in the Sb2Se3-based quasi homojunction solar cells. All simulations, performed in this study, are done by SCAPS device simulation software under standard AM1.5G one Sun illumination.

Thiocyanate‐ and Thiol‐Functionalized p‐Doped Quantum Dot Colloids for the Development of Bulk Homojunction Solar Cells

Progress in device engineering and surface passivation strategies has led to steady progress in colloidal quantum dot (QD) solar cells. Bulk homojunction (BHJ) device architecture has several advantages over the conventional planar junction in developing QD solar cells. Herein, surface ligand chemistry is utilized to control the doping type and dispersibility of oppositely doped PbS QDs to develop BHJ solar cells. Thiocyanate and thiol ligand combination is introduced to develop p‐PbS QD ink, which is blended with halide‐passivated n‐PbS QDs to build BHJ solar cells. It is shown that BHJ solar cells are benefited from high energy offset and higher hole mobility. This leads to the superior carrier extraction from a thicker active layer without compromising fill factor and open circuit voltage. Power conversion efficiency has reached 10.7% in 530 nm‐thick BHJ solar cells, a 24% improvement over the best performing planar solar cells. With the help of the 1D solar cell capacitance simulator, it is shown that a 15% efficient QD solar cell can be realized by further improving the hole mobility above 0.1 cm2 V−1 s−1.

Formation of van der Waals Stacked p–n Homojunction Optoelectronic Device of Multilayered ReSe2 by Cr Doping

AbstractThe formation of p‐ or n‐type material via impurity doping should be crucial and essentially prior to the establishment of junction devices in semiconductor processing. Especially in a 2D transition‐metal dichalcogenide (TMD), dopant selection for growing p‐ and n‐type TMD semiconductors may suffer much higher difficulty and complexity than conventional Si and III–V compounds owing to the complicated valences occurred in transition metals. Different amount of chromium doped in ReSe2 interestingly showing dissimilar carrier types of p‐ReSe2 with Cr 10% and 20% doping and n‐ReSe2 with Cr 0%, 1%, and 5% doping, respectively, is presented here. According to structural and optical characterization, the crystal structure and bandgap of the Cr‐doped ReSe2 remain unchanged in which a deeper donor of Cr6+ can exist in n‐ReSe2 (1% and 5%) while a shallow acceptor of Cr3+ may appear in p‐ReSe2 multilayer (10% and 20%). A p–n homojunction light‐emitting diode made by stacking multilayered n‐ReSe2 (Cr 0%) and p‐ReSe2 (Cr 20%) is first fabricated, and it emits an electroluminescence of ≈946 nm from the band edge. Another p–n homojunction solar cell is also manufactured to exhibit a maximum axial conversion efficiency of η ≈ 1.05% along with the b‐axis polarization of ReSe2.

Stability Improvement of Perovskite Homojunction by Inhibiting the Diffusion of Doping Defects

Perovskite homojunction can promote the separation and oriented transportation of the photocarriers through the built‐in electric field, and weaken the dependence of solar cells on the charge transport layer. Although the perovskite homojunction shows great advantages in improving device efficiency, it retains the inherent poor stability of perovskite materials. Herein, it is found that donor defects (MA+ interstitial, I− vacancy, etc.) in the n‐type layer are prone to compensate the acceptor defects (MA+ vacancy, I− interstitial, etc.) in the p‐type layer. This compensation behavior results from the diffusion of doping defects driven by a concentration gradient, which leads to the weakening of the built‐in electric field. Furthermore, phenethylammonium iodide is introduced into the perovskite homojunction to inhibit the defect diffusion, which enhances the stability of the homojunction and the corresponding solar cells. After modification, the efficiency of perovskite homojunction solar cells is improved from 8.60% to 9.60%, and retains 80% (standard ≈30%) of initial efficiency after 1000 h aging.