Thin Film Solar Cells Research Articles

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.

Optimizing Na2EDTA Concentration for Enhanced Properties of SILAR - Deposited CTS Thin Films

Abstract This study investigates the impact of varying Na2EDTA concentrations on the properties of copper tin sulfide (CTS) thin films deposited on soda lime glass substrates using the successive ionic layer adsorption and reaction (SILAR) method. The aim is to optimize CTS thin film growth for photovoltaic technology applications. CTS thin films were prepared using SILAR with Na2EDTA concentrations of 0.01M, 0.04M, and 0.07M, resulting in samples CTS01, CTS04, and CTS07. Characterization techniques included XRD, SEM, EDAX, FTIR, I-V curves, transmittance spectra, and Tauc plots. The results reveal significant variations in film properties with changing Na2EDTA concentration. XRD patterns indicate polycrystalline films with an orthorhombic CTS phase. SEM images show smooth, dense films with localized clusters. FTIR spectra detect hydrocarbon chains, aromatic rings, and hydroxyl or ether groups. The I-V curves of three samples (CTS01, CTS04, and CTS07) show a voltage-dependent transition from semiconducting to ohmic behavior. The CTS01 exhibits superior conductivity (3.13x10-5/Ωm), while the samples' resistance and conductivity values show an inverse relationship. Transmittance curves display low UV transmittance and high visible transmittance,suggests that the samples are highly absorptive in the UV range and become more transparent in the visible range, indicating potential applications in optical filtering and photovoltaic devices. Tauc plots estimate band gap energies of 3.66, 3.89, and 3.23 eV, indicating high band gap energies suitable for buffer layers in solar cells. The correlation between band gap energy and crystallite size as a function of Na2EDTA concentration is also observed. The study demonstrates the importance of optimizing Na2EDTA concentration for achieving high-quality CTS thin films with desirable properties for photovoltaic applications. The findings highlight the potential of CTS thin films for solar cells, optical filtering, and photonic devices.

Exploring Sb2S3 as a hole transport layer for GeSe based solar cell: A numerical simulation

Abstract Germanium selenide (GeSe) and antimony sulfide (Sb2S3) both are technological intriguing semiconductor material for green and economical photovoltaic devices. In this study, GeSe and Sb2S3 have been utilized as the absorber layer and hole transport layer, respectively, to constructed a heterojunction thin film solar cell consisting of FTO/TiO2/GeSe/Sb2S3/Metal. The GeSe and Sb2S3 are binary compounds and can adopt the same film deposition method, for instance, thermal evaporation, which is expected to improve process compatibility and to reduce production costs. The TiO2 (electron transport layer) and Sb2S3 can form small spike-like conduction band offset and valence band offset with the GeSe, respectively, which possesses potential to suppress carrier recombination at the heterointerfaces. Subsequently, the effects of main functional layer material parameters, heterointerface characteristics and back contact metal work function on the performance parameters of the proposed solar cell were simulated and analyzed using wxAMPS software. After numerical simulation and optimization, the proposed solar cell can reach an open circuit voltage of 0.872 V, a short circuit current of 40.72 mA·cm-2, a filling factor of 84.16%, and a conversion efficiency of 28.35%. According to the simulation results, it is anticipated that the Sb2S3 can serve as a hole transport layer for GeSe based solar cell and enable device to achieve high efficiency. Simulation analysis also provides some meaningful references for the design and preparation of heterojunction thin film solar cells.

Computational analysis of a Cu3VS4-based solar cell with a V2O5 back surface layer

This study has described the development and computational evaluation of Cu3VS4 (CVS) based highly potential thin film solar cell where ZnS is exploited as the transparent layer and V2O5 as the back surface field (BSF) layer, respectively, to form the n-ZnS/p-Cu3VS4/p + -V2O5 hetero-junction. The investigation has highlighted the significant influence of the V2O5 BSF layer on the device performance. The standalone n-ZnS/p-Cu3VS4 device exhibits an open circuit voltage (VOC) of 0.87 V, a short circuit current (JSC) of 33.89 mA/cm2, a fill factor (FF) of 86.72%, and a power conversion efficiency (PCE) of 25.68%. The incorporation of the V2O5 BSF layer has enhanced the PCE to 28.33%, where VOC reached 0.94 V, JSC to 34.39 mA/cm2, and FF to 87.47%. This improvement in VOC has been attributed to the V2O5 BSF layer, leading to increased built-in potential and reduced surface recombination velocity at device interfaces. These findings suggest promising prospects for advancing high-efficiency CVS dual-heterojunction (DH) PV cells in the coming days.

Photovoltaic Efficiency Enhancement of Indium-Free Wide-Bandgap Chalcopyrite Solar Cells via an Aluminum-Induced Back-Surface Field Effect.

Wide-bandgap chalcopyrite materials are attractive candidates for a wide variety of energy conversion devices such as the top cell of tandem-type photovoltaic devices and photoelectrochemical water splitting hydrogen evolution devices. Nevertheless, simultaneous realization of high open circuit voltage (VOC) and high fill factor (FF) values has been challenging, and thus, the photovoltaic performance has been limited. In this article, high VOC and high FF values of wide-gap chalcopyrite CuGaSe2 thin-film solar cells are simultaneously demonstrated using an aluminum-induced back-surface field effect. An independently certified photovoltaic efficiency of 12.25% was obtained from an elemental In-free CuGaSe2:Al (bandgap energy ∼1.7 eV) solar cell (VOC: 0.959 V, short circuit current density: 17.64 mA cm-2, FF: 72.5%). In addition, an over 1 V-VOC CuGaSe2 cell (FF: 74.5%) was obtained even with the use of a conventional CdS buffer layer. Although incorporation of aluminum often leads to degradation of the chalcopyrite solar cell performance, the addition of a small amount of aluminum is found to be effective in enhancing wide-gap chalcopyrite photovoltaic performance.

Strategies to Enhance the Performance of Cu(In,Ga)(S,Se)2 Thin-Film Solar Cells by Doping Approaches

Strategies to Enhance the Performance of Cu(In,Ga)(S,Se)2 Thin-Film Solar Cells by Doping Approaches

Efficiency Improvement on Indium Tin Oxide Films for Dye-Sensitized Solar Cell Using Oxygen Plasma by Bias-Magnetron RF Sputtering Process

Dye-sensitized solar cells (DSSCs) are among the most widely studied thin-film solar cells because of their cost-effectiveness, low toxicity, and simple fabrication method. However, there is still much scope for replacing current DSSC materials due to their high cost, low volume, and lack of long-term stability. Accordingly, indium tin oxide (ITO)-nanorod films were fabricated by electron (E)-beam evaporation using the glancing angle deposition method in this study. Then, the ITO-nanorod was treated with oxygen plasma via a bias-magnetron radio-frequency (RF) sputtering process to improve the efficiency of DSSCs under a varying gas flow rate of 20, 40, 60, 80, and 100 sccm. The field emission scanning electron microscopy (FE-SEM) investigation of the ITO film structure revealed that the obtained nanorod structures have slightly different diameters. At the same time, an increase in the oxygen flow rate resulted in a rougher film surface structure. In this, the lower sheet resistance was received because of rougher morphology. When comparing the DSSCs efficiency (η) test results, we found that at a gas flow rate of 100 sccm, the highest efficiency value showed 9.5%. On the other hand, the ITO-nanorod without plasma treatment exhibited the lowest η. Hence, plasma technology can be practically applied to improve the η of DSSC devices. This study will be a prototype of a highly advanced solar cell manufacturing method for the solar cell industry.

SCAPS numerical modeling of CBTS/WO3 thin film solar cell

The quaternary compound Cu2BaSnS4 (CBTS) has emerged as a suitable and attractive light-harvesting material due to its promising optoelectronic features as well as nontoxic and low-cost constituent elements. Yet efficiency of CBTS-based solar cells did not reach the Shockley-Queisser limit. Here, what we believe to be a novel structure ITO/WO3/CBTS heterojunction solar cell is designed and modeled using a solar cell capacitance simulator in one-dimension (SCAPS-1D). In this work, a what we also believe to be a novel WO3 as a buffer layer is proposed for the first time for the efficiency enhancement of CBTS thin film solar cells. Numerical investigation of the performance of CBTS-based solar cells without and with cuprous oxide (Cu2O) back surface field (BSF) is explored. The impact of thickness, doping density, bulk, and interface defect density of an absorber, buffer and window layer, working temperature, shunt and series resistance, back contact work function, and back surface recombination velocity were analyzed and optimized without and with the BSF layer. In this work, the optimized solar cell achieved an efficiency of 18.8%, fill factor (FF) of 83.79%, short-circuit current density (JSC) of 15.99 mA/cm2, and open circuit voltage (VOC) of 1.4 V without Cu2O BSF layer at optimal CBTS absorber and WO3 buffer layer thickness of 2 µm and 0.04 µm respectively. Furthermore, the efficiency boosted to 21.12% with VOC of 1.43 V, JSC of 16.8 mA/cm2 and FF of 87.77% by inserting 0.1 µm Cu2O BSF layer. Therefore, these results will facilitate the fabrication of an efficient and low-cost CBTS-based solar cell with promising WO3 and Cu2O as buffer and BSF layer, respectively.

Impact of graded CIGS absorber layer on Cd-free CIGS thin-film solar cell performance: numerical optimization

Abstract This paper investigates replacing the CdS buffer layer with (Zn, Mg)O and Zn(S, O) double buffer layers. To increase the efficiency of the structure, our strategy involves numerically studying and comparing three types of CIGS bandgap absorber layers: FB (Flat Band), Double Gradient Bandgap (DG) with a high bandgap near the Mo contact (back side), a low bandgap near the buffer layer (front side), and a minimum bandgap between them, and Simple Gradient Bandgap (SG) with a high bandgap near the Mo contact (back side) and a low bandgap near the buffer layer (front side). Each type features different linear graded profiles in the thickness direction to determine the optimal bandgap gradient of the CIGS layer. The performance of the three types is numerically analyzed using the SCAPS-1D simulator. Simulation enables us to test multiple structural combinations efficiently, saving both time and money, while providing results that guide experimental research. The proposed device structure is composed of the following layers: ZnO:Al/n-Zn1-xMgxO/n- ZnSxO1-x/p- Graded-CuIn1-xGaxSe2 /Mo. To study the effects of linear bandgap gradient distribution of Ga⁄((Ga+In) ) ratio according to the thickness direction on CIGS solar cell performance, the electrical properties of the proposed CIGS model were initially matched with experimental data to confirm the structure's accuracy. It was found that the Double Gradient Bandgap (DG), with maxima of 1.44 eV at the back side (near Mo contact), 1.238 eV at the front side (near n-type buffer layer interface), and a minimum of 1.154 eV at a position of 1.7 µm from the back side, has a higher efficiency than the other structures with 26.22% (Voc = 0.8134 V, Jsc = 37.82 mA/cm², FF = 85.21%). Optimizing the bandgap gradient of the CIGS absorber layer helps improve the efficiency of CIGS solar cells. 

Achieving 34 % efficiency with a dual-absorber solar cell design using CaRbCl3 and Ca3NCl3 perovskites

This study’s DFT calculations show that the direct bandgaps of perovskite CaRbCl3 and Ca3NCl3 are 1.386 eV and 1.430 eV, respectively, confirming their semiconducting nature. The study also provides density of states and dielectric constant data for these materials. In photovoltaic (PV) technology, perovskites are highly valued as solar absorber materials for their exceptional optical properties, low cost, high efficiency, and lightweight design. This study presents a structure (Al/FTO/CdS/dual absorber (CaRbCl3/Ca3NCl3)/V2O5/Au) incorporating a CdS electron transport layer (ETL) and a V2O5 hole transport layer (HTL) with a double perovskite absorber layer (DPAL) of CaRbCl3 and Ca3NCl3 using SCAPS-1D. The results show that the DPAL-based perovskite solar cell (PSC) outperforms single-layer PSCs, with significant efficiency gains when HTL is included. The study thoroughly examines the effects of layer thickness, doping levels, and defect densities on key electrical parameters such as VOC, JSC, FF, and PCE. It also explores J-V and QE characteristics and the impact of temperature. The ideal absorber thickness for achieving the highest PCE is 500 nm for CaRbCl3 and 600 nm for Ca3NCl3, combined with a doping density of 1 × 1017 cm−3, a defect density of 1 × 1011 cm−3 and interface defect density of 1 × 1010 cm−2. While single-absorber solar cells achieve maximum efficiencies of 24.40 % (CaRbCl3) and 24.02 % (Ca3NCl3), the DPAL setup reaches an optimized efficiency of 27.66 %, further increasing to 34.39 % with a VOC of 1.295 V, FF of 83.95 %, and JSC of 31.63 mA/cm2 when using V2O5 HTL. This research provides valuable insights and a practical strategy for developing cost-effective CaRbCl3/Ca3NCl3 thin-film solar cells.

Optimization of CTS Thin Film Solar Cell: A Numerical Investigation Based on USP Deposited Thin Films

Optimization of CTS Thin Film Solar Cell: A Numerical Investigation Based on USP Deposited Thin Films

Enhancing photovoltaic performance of GeSe thin film solar cells by photogenerated carriers redistribution via Cu doping

Enhancing photovoltaic performance of GeSe thin film solar cells by photogenerated carriers redistribution via Cu doping

A Comprehensive Modeling on MoS2 Interface and Defect Engineering in CZTS Thin Film Solar Cells

This work uses the SCAPS-1D modeling program to examine the effects of faults in the molybdenum Disulfide (MoS2) layer and the MoS2 interface on the electrical performance of CZTS solar cells. To get an ideal energy gap (Eg) of 1.3 eV and a carrier concentration (CC) of 1014 cm⁻³, the research attempts to optimize the CZTS absorber layer. By maintaining a consistent doping level with 1016 cm-3 ≤ CC and an Eg within 1.6 eV < Eg ≤ 1.8 eV for the MoS2 film, the work also investigates the possibility of increased efficiency in CZTS/MoS2 devices. The study results indicate that open circuit voltage (VOC) and Efficiency (Eta-η) parameters are improved by a p-type MoS2 interface, indicating a promising development for CZTS solar systems. Nonetheless, n-type MoS2 suggests a compromise with a reduction in the fill factor. The study emphasizes the stability benefits of a p-type MoS2 interface as well as the importance of surface recombination velocity. The study also considers phase transitions that occur during the manufacture of devices, highlighting the intrinsic n-type character of MoS2 and the importance of experimental methods in CZTS device optimization. After analyzing the effects of defects on carrier density, depletion width, and quantum efficiency, the study concludes that enhancing the performance of CZTS solar cells requires an acceptor-type interface with p-type MoS2. With recombination resistances of 443.92 Ω cm2, 1530.33 Ω cm2, 81.54 Ω cm2, and 93.82 Ω cm2, the SCAPS model shows zero series resistance at a particular site for the fundamental, optimized design using n-MoS2 and p-MoS2. In the end, the work sheds light on the possibilities for additional experimental studies to advance the technology of CZTS solar cells.

Effect of substrate temperature on the performance of Sb2Se3 thin film solar cells fabricated by chemical-molecular beam deposition method

Antimony triselenide (Sb2Se3) stands as a promising candidate for photovoltaic (PV) applications due to its favorable material- and optoelectronic properties. However, the realization of further advancements in device efficiency is hindered by the substantial deficit in open-circuit voltage (VOC) attributed to the presence of multiple defect states and detrimental recombination losses.In this work, solar cells based on Sb2Se3 absorber layers deposited by chemical-molecular beam deposition method at substrate temperatures of 400 °C, 450 °C, and 500 °C. Due to the precise control of the Sb/Se ratio, Sb2Se3 thin films with stoichiometric composition were obtained, which was confirmed by energy-dispersive X-ray spectroscopy. The effect of substrate temperature on the morphology and electrical properties of Sb2Se3 thin-films were characterized by scanning electron microscopy and hot probe method. The PV performance of Mo/Sb2Se3/ZnCdS/CdS/ZnO/ITO/Au devices were investigated by current-voltage characteristics, and external quantum efficiency. The conductivity values tend to increase from 1.2 × 10–6 to 4.6 × 10–4 (Ω cm)-1 as the substrate temperature increased. Whereas, the trap-state density was determined between 7.3 × 1013 – 1.7 × 1014 cm-3 in the absorber layer by the space charge limited current method. Ultimatety, it has been shown that defect densities in Sb2Se3 films can be suppressed to some extent by optimizing the substrate temperature. Best solar cell performance of 5.36%, resulting from VOC of 476 mV, short-circuit current densit of 22.97 mA/cm−2, and fill factor of 49% at the substrate temperature of 450 °C.

Optimization of the solar cell based on cadmium telluride by adding the CdSeTe absorbing layer (heterostructure simulation)

Cadmium telluride solar cells are among the most common devices for photovoltaic applications. However, the energy conversion efficiency of these elements remains insufficiently high. Using the SCAPS programming environment, research and optimization of a classical thin-film solar cell based on CdTe were carried out. The structure of this element consisted of ITO as a transparent conductive contact, a cadmium sulfide (CdS) layer, and a cadmium telluride (CdTe) absorber layer with a metal contact. To optimize this structure in terms of power conversion efficiency, the influence of the thickness and concentration of acceptor impurities in the CdTe absorbing layer, as well as the influence of the thickness and concentration of donor impurities in the CdS buffer layer, were considered. It was established that the optimal thicknesses for the CdS buffer layer and absorption CdTe layers are 50 nm and 3000 nm, respectively. An additional CdSeTe layer between the CdS and CdTe layers has been proposed as one of the optimization options to improve the device efficiency. The main photovoltaic parameters of such a solar cell were analyzed depending on the thickness of the CdSeTe layer and its selenium content. It has been demonstrated that adding CdSeTe solid solution to the 1500 nm thick CdTe absorber layer increases the efficiency of the solar cell by 6.84 %. The main photovoltaic characteristics of CdS/CdTe and CdS/CdSeTe/CdTe solar cells were compared. The results showed that the simulated CdS/CdSeTe/CdTe structure provides better photoconversion efficiency in the AM1.5G light spectrum compared to the classical CdS/CdTe structure. Such elements can be used to form highly efficient solar panels

Design and simulation of highly efficient CZTS/CZTSSe based thin-film solar cell

Thin-film solar cells are a substitute for more common crystalline silicon solar cells, which consist of thin semiconductor layers. Thin-film materials comprise direct bandgap and can absorb sunlight more efficiently than silicon. In this article, a double-absorber-based thin-film solar cell comprising CZTS/CZTSSe is designed and optimized through numerical simulation. The proposed solar cell structure consists of a transparent window layer made of aluminum-doped zinc oxide, followed by an intrinsic zinc oxide layer, an n-type cadmium sulfide layer, and a p-type combined absorber layer of copper zinc tin sulfide (Cu2ZnSnS4) (CZTS) and copper zinc tin sulfur-selenium alloy (Cu2ZnSn(S,Se4)) (CZTSSe). The structure is further optimized by introducing two interfacial layers between CZTSSe/CZTS and CZTS/CdS. The highest conversion efficiency is achieved by adjusting the thicknesses of the layers, the doping densities in different layers, and the defect densities in the two absorber layers. The optimized model, with a total thickness of 2.01 μm, demonstrates an open-circuit voltage (Voc) of 0.7669 V, a short-circuit current (Jsc) of 48.57740 mA/cm2, a fill factor (FF) of 70.61%, and efficiency (η) of 26.31%. These results suggest that CZTS is a promising candidate for replacing other thin-film photovoltaic materials, such as CdTe. The proposed double-absorber thin-film solar cell optimizes doping concentration, thickness, and defect density to enhance performance metrics and efficiency while utilizing non-toxic materials to promote cost-effective, environmentally friendly energy solutions.

In-Silico Design and Optimization of p-BaSi₂/n-Bi₂S₃ Heterojunction for Enhanced Photovoltaic Performance

This study aims to explore the integration of Bi2S3 as an electron transport layer (ETL) in BaSi2-based thin-film solar cells for the enhanced performance. Using the globally accepted SCAPS-1D simulation tool, a novel device architecture consisting of Al/SnO2:F/Bi2S3/BaSi2/Ni was systematically designed and optimized. Key optimization parameters include the thicknesses, carrier concentrations, bulk defect densities of each layer, interface defects, operating temperature, and the influence of series and shunt resistance on overall efficiency. The simulation results reveal that a BaSi2 layer with an optimized thickness of 1 µm and a doping concentration of 5 x 1019 cm-3, yields noteworthy outcomes. Specifically, champion efficiency (

Probing into the low efficiency of CdS/SnS-based solar cells and remediation through surface treatments

Tin sulfide (SnS) is a highly promising photovoltaic absorption material in thin-film solar cells with abundant reserves, environmental friendliness, low cost and long-term stability. An efficiency of up to 4.8 % has been achieved for SnS absorber/CdS heterojunction solar cells where the CdS buffer layer is usually obtained by chemical bath deposition. However, current CdS/SnS devices often suffer from severe interface recombination loss, which deteriorates device performance. This report focuses on the CdS film surface to identify performance-degrading factors for CdS/SnS-based solar cells. XRD and XPS reveal numerous oxides on freshly fabricated CdS films increasing surface roughness and reducing conductivity. Herein, a method based on ammonium sulfide (AS) chemical treatment is proposed, which can effectively reduce the oxide content on the surface of CdS and optimize the band alignment, leading to the facilitation of charge carrier transport and the suppression of interface recombination. Consequently, the PCE of the FTO/CdS/SnS/Ag device is enhanced about three times (from 0.18 % to 0.47 %) with excellent moisture stability.

A Review of Simulation Tools for Thin-Film Solar Cells.

Unlike current silicon-based photovoltaic technology, the development of last-generation thin-film solar cells has been marked by groundbreaking advancements in new materials and novel structures to increase performance and lower costs. However, physically building each new proposal to evaluate the device's efficiency can involve unnecessary effort and time. Numerical simulation tools provide a solution by allowing researchers to predict and optimize solar cell performance without physical testing. This paper reviews thirteen of the main numerical simulation tools for thin-film solar cells, including SCAPS, AMPS, AFORS-HET, ASPIN3, GPVDM, SESAME, SILVACO, SENTAURUS, and ADEPT. This review evaluates each tool's features, modeling methods, numerical approaches, and application contexts. The findings reveal notable differences in material modeling, numerical accuracy, cost, and accessibility among the tools. Each tool's strengths and limitations in simulating thin-film solar cells are highlighted. This study emphasizes the necessity of selecting suitable simulation tools based on specific research requirements. It provides a comparative analysis to assist researchers in choosing the most effective software for optimizing thin-film solar cells, contributing to advancements in photovoltaic technology.

Trends Research Characterization of TiO2 Thin Films as Solar Cell Materials (2015-2024): A Systematic Review

Research in the field of solar cells continues to increase along with the development of the times and human needs for renewable energy sources. One of the fields of study that is often used as a research topic is the development of Thin Film Solar Cells or known as Thin Film Solar Cells (TFSC). This research aims to identify and analyze research trends of synthesis of Ti02 thin films as solar cell materials. This research method is descriptive and analytical. The data used in this research was obtained from documents indexed by Google Scholar from 2015-2024 using Publish or Perish and Dimension.ai. Research procedures use PRISMA guidelines. The data identified and analyzed are the type of publication, publication source, and the title of research on synthesis of Ti02 thin films as solar cell materials that is widely cited. The data analysis method uses bibliometric analysis assisted by VOS viewer software. The results of the analysis show that research trend on synthesis of TiO2 thin films as solar cell materials indexed by Google Scholar from 2015 to 2024 has experienced increases and decreases. There are many documents in the form of articles, proceedings, chapters, preprints, monograph and edited books that discuss research about synthesis of Ti02 thin films as solar cell materials. Key words that are often used in research about it are dye sensitized cell, electrode, electron, characterization, etc.