Graded Band Gap Research Articles

Performance study of a graded band gap solar cell based on CZTS(SE)

The large-scale development of photovoltaic electrical energy is still conditional on lowering the cost of solar cells and increasing their efficiency. Since the realization of the first photovoltaic cell, several research works have been initiated to solve this problem, especially thin film solar cells. Thin film solar cells represent promising approaches for cutting production costs include the use of thin films solar cells. This generation's benefit is that they frequently employ semiconductor materials with direct band gaps, which have exceptionally high absorption coefficients. In this context, thin film solar cells based on a material (CZTS) play a role at low cost. CZTS (Cu2ZnSnS4) is a quaternary semiconductor of the I2-II-IV-VI4 type, it is composed of abundant materials. It is a new type of absorber for thin film solar cells. Copper-zinc-tin-sulfur (CZTS) is a semiconductor with excellent photovoltaic properties such as direct gap, high absorption coefficient, and has an optimal band energy highly desired in photovoltaic material. In addition, the cells using CZTS are non-toxic and inexpensive materials. Currently, several researches have been devoted to develop and improve the electrical characteristics (particularly efficiency) of CZTS solar cells which show a theoretical limit efficiency of 32.4 % Shockley Quisser, while the experimental efficiency is 14.9% In this paper, we propose a potential efficiency Cu2ZnSn(S,Se)/CdS (CZTS) solar cell design based on graded band-gap that can offer the benefits of improved absorption behavior and reduced recombination effects. Moreover, our approach is based on analytical modeling to determine the optimal band gap profile of the absorber layer of the CZTS material to improve the photovoltaic conversion efficiency. The results of this study show that the use of a graded layer shows a decrease the recombination rate which leads to an increase in current from 22.16 mA/cm2 (for a standard CZTS cell) to 30 mA/cm2 (for a graded cell) and by therefore an improvement in efficiency from 10.9 % to 15.25 %

A theoretical study on the insights of designing and optimization of a CsSn(IxBr1-x)3 based solar cell

This work focuses on designing and optimizing a lead-free perovskite solar cell. The significance of band gap grading in obtaining better performance of the solar cell was studied in detail with CsSn(IxBr1-x)3 () being used as the active absorber material. The device showed a maximum power conversion efficiency (PCE) of when the interfacial defects were not considered. The optimum thickness was obtained to be 1 μm, and the corresponding doping concentration was 1020 cm-3. Further, a detailed discussion on the band diagrams, electric fields, and different recombination processes has been carried out in this work to get an idea about the varying PCE values at different operating conditions. The presence of Shockley-Read-Hall (SRH) recombination at various temperature values was observed, which partially contributed to the reduction in PCE values at higher temperatures. This work also discusses briefly about the probable losses involved with the device, which may be considered as the plausible reasons for obtaining PCE values less than the SQ limit. This information opens up a wide window for researchers to experimentally fabricate solar cells with proper cautions so that a device with PCE value exceeding Shockley Quisser (SQ) limit can be made available commercially.

Towards highly efficient thin-film solar cells with a graded-bandgap CZ TSSe layer. Part II: Piecewise-homogeneous bandgap grading

Abstract In Part I, we optoelectronically optimized a thin-film solar cell with a graded-bandgap CZTSSe photon-absorbing layer and
a periodically corrugated backreflector, using the hybridizable discontinuous
Galerkin (HDG) scheme to solve the drift-diffusion equations.
The efficiency increase due
to periodic corrugation was minimal, but significant improvement was achieved
with a nonlinearly graded bandgap. Due to occasional failures of the HDG
scheme from negative carrier densities, we developed a new computational scheme using the finite-difference
method, which also reduced the overall computational cost of optimization. Later, a normalization error
was discovered in the electrical submodel in Part I, but it did not alter the overall conclusions. We have
now re-optimized the solar cells with (i) a homogeneous bandgap, (ii) a linearly graded bandgap, or (iii)
a nonlinearly graded bandgap, and (iv) piecewise-homogeneous bandgap which is easier to implement than a
continuously graded bandgap.
An efficiency of 13.53\% is predicted with a three-layered piecewise-homogeneous CZTSSe 
layer. Furthermore, concentrating sunlight by a factor of one hundred can boost the efficiency to 16.70\%
 with the
piecewise-homogeneous bandgap.

Enhancing performance of Cu2ZnSn(S, Se)4 solar cells via non-uniform gradient and flat bands induced by Cd substitution

Severe carrier recombination at the back (Mo/CZTSSe) and front (CZTSSe/CdS) interfaces is one of the most important reasons hindering the development of open-circuit voltage (VOC) and fill factor (FF) in Cu2ZnSn(S, Se)4 (CZTSSe) solar cells. In this study, we intentionally introduced a non-uniform distribution of Cd impurities into the middle of the absorber layer, designing and fabricating a CZTSSe solar cell with a non-uniform “V”-shaped graded bandgap structure. This structure is aimed at providing a favorable back electric field, reducing carrier recombination at the Mo/CZTSSe interface. The PCE of the CZTSSe solar cell improved from 8.88 % to 10.89 %, significantly enhancing FF and VOC. Additionally, we utilized the solar cell simulation software SCAPS-1D to simulate the position of the minimum point in the V-shaped graded bandgap and combined this with experimental results to explore the effect of Cd doping location on the performance of CZTSSe solar cells. It’s worth noting that the non-uniform Cd-doped solar cell displayed exceptional stability, demonstrating an efficiency enhancement from 10.28 % to 10.94 % after being exposed to air for 30 days.

Numerical optimization of cesium tin-germanium triiodide/antimony selenide perovskite solar cell with fullerene nanolayer

SCAPS-1D platform was used to simulate a solar cell with FTO/CdS/Sb2Se3/CuInSe2/Au structure which was recently fabricated by Liu et al. (2022) [1] [Journal of Energy Chemistry68 521–528 (2022)] and a very similar result was obtained. Reported parameters were Fill Factor (FF) = 53.60 %, short circuit current density (JSC) = 26.18 mA/cm2, open circuit voltage (VOC) = 0.37 V, and power conversion efficiency (PCE) = 5.19 %, while simulated parameters were FF of 54.68 %, JSC of 27.54 mA/cm2, VOC of 0.36 V, and PCE = 5.55 %. The advancements have been evaluated by analyzing FTO/CdS/Sb2Se3/CuInSe2/Au and FTO/C60/Sb2Se3/CuInSe2/Au configurations, serving as the reference cells. To improve the cell performance, the CdS layer was replaced with another layer (C60) which shows excellent electron transport properties. Replacing the CdS layer with C60 led to an increase in the power conversion efficiency by 65 % (from 5.55 % up to 9.20 %). In photovoltaic systems, the PCE constitutes a pivotal parameter that can be enhanced through the absorption of a broad spectrum of incident photons. Consequently, the implementation of two absorber layers within a solar cell, each characterized by a graded band gap energy, enables the capture of solar photons over a more extensive spectral range. Therefore, a perovskite containing a band gap of 1.5 eV, lead-free, and Sn-based was used as the second absorber layer in the device. Therefore, a solar cell with FTO/C60/CsSn0.5Ge0.5I3/Sb2Se3/CuInSe2/Au structure was simulated, and significant results were achieved. Results showed that inserting the CsSn0.5Ge0.5I3 layer led to an increase in PCE up to 11.42 %.

Fabricating Cu2Zn(SnxGe1-x)Se4 thin-film solar cells with back surface Ge grading by magnetron sputtering

In this paper, an approach of forming a band gap gradient by depositing a layer of Ge between the Mo layers by magnetron sputtering is proposed. The diffusion depth of the Ge into Cu2ZnSnSe4 (CZTSe) thin film can be effectively controlled by the Mo transition layer, resulting in the formation of Cu2Zn(SnxGe1-x)Se4 (CZTGSe) thin film with a band gap grading along the back surface. To validate the formation of the Ge gradient in the absorber, energy dispersive spectrometer line scanning and grazing incidence X-ray diffraction were performed. Furthermore, the impact of Ge layer on the morphologies of CZTSe was assessed using scanning electron microscopy. As a result, the introduced Ge layer formed a Ge grading along the back surface and improved the crystal quality of the absorber. Compared to CZTSe solar cells, the power conversion efficiency (PCE) of CZTGSe solar cells with a Ge gradient improved from 5.79 % to 9.28 %.

Bandgap-graded Cu2Sn1-xGexS3 thin film solar cells prepared by sputtering SnGe/Cu targets

Cu2Sn1-xGexS3 (CTGS) thin films were created through sulfurizing SnGe/Cu precursors deposited by the sputtering method. The effects of different sulfurization conditions on the crystallinity, morphology, composition, optical-electrical properties and chemical information of the CTGS thin films have been investigated in detail. The results demonstrate that the CTGS thin films obtained by using sulfurization temperature at 550 °C for 20min have the best crystal quality and smooth surface morphology with largest grains and the best optical-electrical properties. Meanwhile, CTGS thin films solar cell with the best performance is found that the CTGS film possesses a graded band gap structure, in which the band gap gradually become larger towards the Mo electrode, and the CdS/CTGS hetero-junction interface shows the “type I″ energy band alignment with a “spike-like” structure. As a result, the obtained bandgap-graded CTGS thin film solar cells with the best power conversion efficiency (PCE) of 3.35 (±0.04) % manifest an open-circuit voltage of 389 (±7.78) mV and a short-circuit current density of 26.98 (±0.54) mA cm−2. This work demonstrates a promising route to develop high-efficiency Cu(In,Ga)Se2 or Cu2SnS3-based thin film solar cells.

Maximizing photovoltaic performance of all-inorganic perovskite CsSnI3-xBrx solar cells through bandgap grading and material design

In the modern era of technology, worldwide paradigms have been shifted toward the utilization of green energy. Sun energy is the most astonishing eco-friendly resource of energy and can be harnessed with the help of photovoltaic cells. Hybrid (Organic-Inorganic) perovskite solar cells (PSCs) are emerged with incredible photovoltaic (PV) performance. Nevertheless, a significant challenge lies in their lower stability under diverse environmental conditions. To deal with this challenge, all inorganic cesium-based PSC has been studied and analyzed, results improved stability in comparison to hybrid PSC. However, the noxious nature of lead is deleterious to the environment. So, this work primarily aimed, to study lead-free all inorganic tin-based perovskite compound CsSnI3-xBrx, as the main light absorber layer. Further, to elevate the PV performance of PSC, bandgap grading is performed on CsSnI3-xBrx by varying bromide concentration x from 0 to 3. Bandgap grading encourages the absorption of a wide range of the light spectrum, by modulating bandgap (Eg) / affinity(χ) through the distance of the CsSnI3-xBrx layer. Additionally, it enhances light-generated charge carrier separation and collection by end electrodes. In this work, two different strategies have been adopted, linear and parabolic. During linear grading, the impact of variation in x (0 to 3) has been analyzed over the thickness 50–––500 nm in 10 linear steps for CsSnI3-xBrx. The highest PCE fetched from linearly graded layered FTO / CeO2 / CsSnI3-xBrx / CFTS / Gold PSC is 21.68 %. Similarly, in the parabolic graded absorber layer, the influence of change in the bowing factor (0 to 1), has been analyzed relative to different values of x (0 to 3). With improvement in PV performance, the maximum PCE delivered by parabolic-graded PSC is 23.61 %. Additionally, this work extends to check the compatibility of distinct electron transport layers (ETLs) and hole transport layers (HTLs). Upon analysis, it has been found that the best PV performance was obtained while selecting SnO2 / PEDOT as ETL / HTL respectively.

Optimizing photovoltaic performance: Strategic enhancement of Ag-doped graded CAZTS solar cells achieving 27.3% efficiency

The Ag-doped Cu2ZnSnS4 (CAZTS) based solar cell has been explored, with varying Ag concentrations (x = 0, 0.1, 0.2, 0.3, 0.4) in the composition (Cu1−xAgx)2ZnSnS4. In order to mitigate back surface recombination in CAZTS-based solar cells, a Sn2S3 layer has been incorporated as a back surface field (BSF). Further, the efficiency enhancement employs a bandgap grading approach, elevating efficiency from 15.8 % to 24.7 % compared to devices without the graded structure. Additionally, the thickness and total defect density of the CAZTS layer are optimized. The result demonstrates that the optimized value of the CAZTS layer’s thickness is 1.1 µm, and the defects are 1 × 1012 cm−3. To further enhance the performance, the doping variation of the CAZTS layer has also been investigated. The findings indicate that the maximum efficiency of 27.32 % is attained with a doping value of 1 × 1016 cm−3.

Efficiency enhancement of ultrathin CIGS solar cells by optimal bandgap grading. Part III: piecewise-homogeneous grading

In Parts I [ Appl. Opt. 58, 6067 (2019)APOPAI0003-693510.1364/AO.58.006067] and II [ Appl. Opt. 61, 10049 (2022)APOPAI0003-693510.1364/AO.474920], we used a coupled optoelectronic model to optimize a thin-film CIGS solar cell with a graded-bandgap photon-absorbing layer, periodically corrugated backreflector, and multilayered antireflection coatings. Bandgap grading of the CIGS photon-absorbing layer was continuous and either linear or nonlinear, in the thickness direction. Periodic corrugation and multilayered antireflection coatings were found to engender slight improvements in the efficiency. In contrast, bandgap grading of the CIGS photon-absorbing layer leads to significant enhancement of efficiency, especially when the grading is continuous and nonlinear. However, practical implementation of continuous nonlinear grading is challenging compared to piecewise-homogeneous grading. Hence, for this study, we investigated piecewise-homogeneous approximations of the optimal linear and nonlinear grading profiles, and found that an equivalent efficiency is achieved using piecewise-homogeneous grading. An efficiency of 30.15% is predicted with a three-layered piecewise-homogeneous CIGS photon-absorbing layer. The results will help experimentalists to implement optimal designs for highly efficient CIGS thin-film solar cells.

Tailored Band Alignment for Improved Carrier Transport in Composition-Controlled Sb2(S,Se)3.

Sb2(S,Se)3 is a highly available energy material with a tunable bandgap by adjusting the S/Se ratio. Increasing the Se ratio can enhance the efficiency of Sb2(S,Se)3 solar cells, with a higher short-circuit current (JSC). However, the accompanying decrease in the open-circuit voltage (VOC) restricts further improvement. The defect passivation is important, since it can reduce carrier recombination, enhancing the VOC. In this study, the relevance of the S/Se ratio, defect concentration, and VOC was investigated. The samples with or without the deposition of Se-rich Sb2(S,Se)3 onto S-rich Sb2(S,Se)3 were used for defect characterization. Different surface compositions were confirmed by Raman spectroscopy. The complicated subdefect states of S-rich Sb2(S,Se)3 were shown through photoluminescence and conductive atomic force microscopy, and a decrease in the defect concentration was observed through surface photovoltage. The improvement of JSC via bandgap grading and the simultaneous VOC improvement by defect passivation resulted in efficient cell performance.

Regulating SnZn defects and optimizing bandgap in the Cu2ZnSn(S,Se)4 absorption layer by Ge gradient doping for efficient kesterite solar cells

In recent years, the primary reasons for low efficiency Cu2ZnSn(S,Se)4 (CZTSSe) solar cells have been attributed to SnZn defects and related defect clusters, as well as the balance of absorption layer bandgap for short-circuit current density (Jsc) and open-circuit voltage (Voc). Ge gradient has been theoretically proven to be an effective strategy to change traditional flat bandgap structure and suppress SnZn defects and related defect clusters for improving the device performance of CZTSSe solar cells. However, the potential of Ge gradient has not been fully verified. In this work, Ge doping effectively reduces the formation of SnZn defects and [2CuZn + SnZn] defect clusters in the CZTSSe absorption layer. In addition, it can be found that the construction of the V-type bandgap is the best solution for balancing between Voc and Jsc. By using the bandgap grading strategy, the disparity between the recombination barrier of the junction and the optical bandgap's minimum value is widened, thereby obtaining a large Voc. The V-type doped device has the highest efficiency when Voc is 0.45 V, which can reach 8.03%. This Ge graded substitution method provides an alternative absorption layer structure for improving Voc and the preparation of future high-efficiency kesterite photovoltaic devices.

Quasi-Flat Narrow Bandgap Copper Indium Gallium Selenium Bottom Cell Application in Perovskite/Copper Indium Gallium Selenium Tandem Solar Cells

Cu(In 1− x Ga x ) Se 2 (CIGS) is a promising and ideal material for bottom cell in tandem solar cells, which can break the double junction solar cell’s Shockley–Queisser theoretical efficiency to above 40%. However, the high-efficiency CIGS solar cells deposited by the 3-stage process is normally double grading, leading to an incomplete absorption in the bottom cells. In this study, single bandgap grading and quasi-flat bandgap CIGS solar cells are proposed and fabricated for perovskite/CIGS 4-terminal tandem solar cells, which are more favorable for long-wavelength absorption and higher short-circuit current density J sc . Various characterizations have been performed to investigate the crystallization, crystal defects, composition depth profile, and carrier dynamics of the CIGS thin films. Our study reveals that the performance of CIGS solar cells with high Ga content is worse than expected. Using bandgap engineering, we can obtain CIGS solar cell with an efficiency above 16.5% regardless of the GGI [Ga/(Ga + In)] varying from 0.27 to 0.40. However, CIGS solar cells with less Ga content and low bandgap exhibit superior long-wavelength spectral response, making them more suitable for bottom cell applications in tandem solar cells. In combination with an 18.9% semitransparent inorganic perovskite solar cell, a 25.6% perovskite/CIGS tandem device in 4-T configuration is demonstrated.

N-type Ag2S modified CZTSSe solar cell with lowest Voc,def

The Sn, Zn-doped Ag2S plays a triple role in CZTSSe devices: p–n conversion, front-interface bandgap grading, and defect passivation. This strategy achieved an efficiency of 14.25%, with the Voc of 0.584 V and the lowest Voc,def of 0.228 V.

Exploring the deposition pathway in the notch region of double-graded bandgap ACIGS solar cells

The bandgap widening of Ag-alloyed Cu(In,Ga)Se2 (ACIGS) thin films poses a significant challenge in enhancing their photocurrent. This study demonstrates correlations between element diffusion behavior and notch-point formation in ACIGS films, which ultimately influence the resulting current circuit voltage and fill factor. Our findings delineate a novel approach for fabricating a suitably tailored band gap grading in ACIGS, which serves as a bottom subcell in tandem configuration. This was achieved by modulating a wide range of process temperatures from 340 to 470 °C, which were measured by pyrothermal, to assess the GGI profile during deposition. Experiments were undertaken to variate the second-stage conditions, striving to sustain the photocurrent, mitigate defects, and enhance crystallinity, achieving an impressive performance of 17.7 % without applying post-deposition treatments or anti-reflection coatings. The efficiencies surpassing 8 % were achieved as we measured these cells under a 715 nm long-pass filter, which corresponds to the bandgap of a typical top cell in tandem applications (1.73 eV photon energy). These results emphasize the significance of understanding the deposition temperature and its impact on the properties of ACIGS films, paving the way for further advancements in solar-cell technology.

Tunable, graded band-gap TiO2 thin film solar cell deposited by HIPIMS on flexible substrate

Among various types of thin-film solar cell (TFSC), the amorphous silicon type exhibits low and unstable conversion efficiency. Compound solar cells, on the other hand, are with a shortage of rare metals and toxic metals usage, not to mention unacceptable high deposition temperature. To overcome these problems and material cost consideration, the titanium-based oxide material known as potential photovoltaic material was chosen to develop a novel TFSC. During film deposition, the oxygen flow rate was adjusted to obtain p-TiO/n-TiO2 as the p-n junction, where p-TiO acts as the absorption layer and n-TiO2 as the window layer, whilst in an attempt in this study is to develop a graded bandgap n-TiO2 by progressive control of N2 flow rate to favor the electron-hole pairs separation and thus increased conversion efficiency. Meanwhile, a high-power impulse magnetron sputtering (HIPIMS) technique was used to conduct film deposition for providing high-density plasma that is beneficial for crystalline growth at low temperature. Ultimately, a flexible photovoltaic device composed of [PI/Ni (V)/ p-TiO/Graded bandgap n-TiO2/IZO/Al] is expected to be achieved.Experimental results show that the p-TiO absorption layer obtained at an oxygen/argon flow rate ratio of 0.28 exhibits a higher degree of crystallinity and enlarged grain size, leading to designated electrical properties. The carrier mobility and electrical resistivity are 2.18 cm2/Vs and 8.45 × 10−4 Ω-cm, respectively. The optical bandgap of the absorption layer p-TiO is about 2.27 eV. On the other hand, the n-TiO2 window layer slightly decreases its bandgap energy from 3.20 eV to 3.18 eV when the nitrogen flow rate increases from 0 to 50 sccm though, the increased external quantum efficiency (EQE) and the associated better conversion efficiency is found (in comparison with the intrinsic n-TiO2 window layer). It is undoubtedly contributed by the graded energy gap structure. Ultimately, the assembled photovoltaic device of [PI/Ni(V)/p-TiO/Graded bandgap n-TiO2/IZO/Al] presents an external quantum efficiency of 45 % under 310 nm monochromatic irradiation and photovoltaic efficiency of 0.2 %.

Efficiency improvement of Cu(In(1−x)Ga x )Se2 solar cell using copper barium tin sulfide as back surface field layer and bandgap grading technique

This work proposes the simulation of graded –based solar cell with copper barium tin sulfide (CBTS) compounds as a back surface field (BSF) layer using the SCAPS-1D software. The CBTS BSF layer reduces the charge carrier losses on the back contact side and creates an extra BSF that helps in extracting holes toward the back contact. To utilize the maximum spectrum absorption range, three different grading configurations were analyzed by varying the stoichiometry of . This grading technique significantly improves the device performance such as open circuit voltage (V oc), short circuit current density (J sc), fill factor (FF), and power conversion efficiency by changing the Ga content in the CIGS material. Furthermore, the impact of interface defect recombination velocity at the WSSe/graded-CIGS interface, acceptor density, and bulk defect in the CIGS layer on the device’s performance have been analyzed. The insertion of CBTS as a BSF layer and the bandgap grading technique yield a maximum efficiency of 31.08% for the proposed solar cell. These results will be helpful in the fabrication of highly efficient bandgap graded-CIGS solar cells.

Optoelectronic optimization of graded-bandgap thin-film AlGaAs solar cells. Part II: optimal antireflection front-surface texturing.

In Part I [Appl. Opt.59, 1018 (2020)APOPAI0003-693510.1364/AO.381246], we used a coupled optoelectronic model to optimize a thin-film AlGaAs solar cell with a graded-bandgap photon-absorbing layer and a periodically corrugated Ag backreflector combined with localized ohmic Pd-Ge-Au backcontacts, because both strategies help to improve the performance of AlGaAs solar cells. However, the results in Part I were affected by a normalization error, which came to light when we replaced the hybridizable discontinuous Galerkin scheme for electrical computation by the faster finite-difference scheme. Therefore, we re-optimized the solar cells containing an n-AlGaAs photon-absorbing layer with either a (i) homogeneous, (ii) linearly graded, or (iii) nonlinearly graded bandgap. Another way to improve the power conversion efficiency is by using a surface antireflection texturing on the wavelength scale, so we also optimized four different types of 1D periodic surface texturing: (i) rectangular, (ii) convex hemi-elliptical, (iii) triangular, and (iv) concave hemi-elliptical. Our new results show that the optimal nonlinear bandgap grading enhances the efficiency by as much as 3.31% when the n-AlGaAs layer is 400nm thick and 1.14% when that layer is 2000nm thick. A hundredfold concentration of sunlight can enhance the efficiency by a factor of 11.6%. Periodic texturing of the front surface on the scale of 0.5-2 free-space wavelengths provides a small relative enhancement in efficiency over the AlGaAs solar cells with a planar front surface; however, the enhancement is lower when the n-AlGaAs layer is thicker.

Flexible Stacked Perovskite Photodetectors for High-Efficiency Multicolor Fluorescence Detection.

A flexible, multicolor detector based on stacked perovskite layers with graded band gaps was presented. Different perovskite layers generate a series of photocurrents corresponding to light intensities at different wavelengths. Experimentally, the flexible detector demonstrated acceptable long-term stability and temperature stability in the bending state. To demonstrate the advantages of the flexible multicolor detector in biological applications, a tubular-shaped multicolor fluorescence detector that embraces the sample cell was constructed. As a result, the detection limits of three kinds of CdTe quantum dots (QDs) with central wavelengths of 545, 625, and 730 nm were 0.52, 0.85, and 0.43 nM, respectively, which was significantly improved by more than 10 times compared to those of planar detectors. Additionally, the detector was able to detect three kinds of QDs simultaneously in a mixed solution, and the relative deviation was smaller than 10% compared to the preset concentration. These results demonstrate that the flexible stacked perovskite detector and the tubular-shaped detection configuration hold promise for the simultaneous fluorescent detection of multiple biomolecules.

Optimization and performance enhancement of InP/CIGS/CuI solar cell using bandgap grading

Optimization and performance enhancement of InP/CIGS/CuI solar cell using bandgap grading