Diode Ideality Factor Research Articles

Realization of diode structures on paper: An example of papertronics

A possibility of fabricating paper/Ag/CdTe/Au Schottky and paper/Ag/CdTe/CdS/In p-n junction diode structures has been demonstrated here. Ag (∼5 μm), CdTe (∼50 μm), CdS (∼45 μm), Au and In dots (∼5 μm) were deposited on the cellulose using appropriate stainless-steel masks to obtain the requisite diode structures. The band gaps of the CdTe and CdS layers were ∼1.55 eV and ∼1.45 eV, respectively. Current-voltage (I-V) characteristics of the paper/Ag/CdTe/Au Schottky and paper/Ag/CdTe/CdS/In p-n junction diodes were recorded at room temperature. Ideality factor (n), series resistance (RS) and barrier height (φb) of the respective diodes were computed. The barrier height (φb) and ideality factor (n) computed from current-voltage characteristics were found to be 0.74 eV and 1.8, respectively at room temperature. Series resistance and φb computed by using Cheung-Cheung method were ∼177 Ω and ∼0.45 eV, respectively. They are comparable to the resistance derived from a modified Norde method. The fabricated diodes were reproducible and stable for a few months. These diode structures were tested in an open environment at room temperature and showed no noticeable ageing effect.

A Study on the Impact of Different PV Model Parameters and Various DC Faults on the Characteristics and Performance of the Photovoltaic Arrays

PV systems play a vital role in the global renewable energy sector, and they require accurate modeling and reliable performance to maximize the output power. This research presents a thorough analysis and discussions on the effects of different PV models’ parameters and certain specific faults on the performance and behavior of the photovoltaic systems under different temperature and irradiation conditions. It provides a detailed analysis of how several parameters affect the performance of the PV arrays, for instance, the series resistance, shunt resistance, photocurrent, reverse saturation current, and the diode ideality factor. These parameters were extracted mathematically and verified with the help of wide-ranging simulations and practical experiments. Additionally, the investigation of the effect of DC faults, including line-to-line, line-to-ground, partial shading, and complete shading faults on PV arrays, provides important fundamentals for fault detection and classification, thus improving the efficiency and protection of PV systems. It can, therefore, be stated that the outcomes of this research will assist in the enhancement of PV systems in terms of design, operation, and maintainability of photovoltaic plants, as well as contribute positively to the advancement of sustainable solar energy technology.

Enhanced photodiode performance: Au/boron-dipyrromethene/n-Si/Ag structure unveiling high photosensitivity and efficiency

In this study, the classical boron-dipyrromethene (4,4- difuoro-4-borata-3a-azonia-4a-aza-s-indacene, BODIPY) unit (C1), its halogenated derivative (C2), and disytryl derivative (C3), which are known for their absorption properties in the near-infrared (NIR) region, were synthesized. Chemical and photophysical investigations were carried out to reveal the complex features of the molecules using a range of spectroscopic techniques and their energies were calculated by Density Functional Theory (DFT) with the same basis set. The BODIPY thin films were coated on n-Si substrates using a spin coater to examine the effect of interlayer on photodiode/photovoltaic properties and Au/BODIPY (C1, C2, C3)/n-Si/Ag photodiodes having rectifying behavior were fabricated. The thermionic emission theory (TET) and modified Norde’s functions were utilized to determine the rectification ratio, ideality factor, series resistance, and barrier height values of diodes. The values of barrier height, ideality factor, and rectification ratio at ± 2 V were calculated as 0.81 eV, 1.83 and 2.47x103 for the Au/C1/n-Si/Ag diode, 0.83 eV, 1.63, and 7.06 x103 for the Au/C2/n-Si/Ag diode and 0.84 eV, 1.51 and 2.14x104 for the Au/C3/n-Si/Ag diode in the dark from the TET, respectively. The values of FF (%) and efficiency were calculated as 38 and 1.51 for the Au/C1/n-Si/Ag diode, 47 and 2.03 for the Au/C2/n-Si/Ag diode, and 56 and 3.68 for the Au/C3/n-Si/Ag diode under 100 mW/cm2 illumination, respectively. With remarkable electrical properties, the Au/C3/n-Si/Ag photodiode stood out among the others, performing better in both dark and light conditions. Therefore, the produced diodes based on the BODIPY thin film can be employed as photodiodes/photovoltaics in optoelectronic applications.

Parameters Estimation of Photovoltaic Modules Using Differential Evolution Metaheuristic Method

This paper presents the analysis of the differential evolution (DE) metaheuristic method, which is used to estimate some parameters employed in the equivalent electrical circuit that represents the photovoltaic (PV) cell model. The DE algorithm is an evolutionary algorithm that can be designed to search global optimal points with fast convergence time and present accurate results, requiring few control variables to be set. The accuracy of reproducing the characteristics of the PV module depends on the knowledge of some PV cell model parameters, such as series and shunt resistances, diode ideality factor, and diode reverse saturation current. Once the referred parameters are not usually given in the manufacturers' datasheet, their determination can be achieved by the DE algorithm, employing data and the current-voltage (I-V) characteristic curve provided by the PV module manufacturers. The technique is designed to minimize the error between the reference I-V curve and the I-V curve reproduced by the DE algorithm. Through simulation results, the feasibility of the DE algorithm to estimate the desired parameters of a PV cell is validated, and the algorithm's performance to reach the best solution with fast convergence and a small iteration number is evaluated.

Characteristics of grafted monocrystalline Si/ β -Ga2O3p–n heterojunction

Beta-phase gallium oxide (β-Ga2O3) has exceptional electronic properties with vast potential in power and radio frequency electronics. Despite the excellent demonstrations of high-performance unipolar devices, the lack of effective p-type dopants in β-Ga2O3 has hindered the further development of Ga2O3-based bipolar devices. In this work, we applied the semiconductor grafting approach and fabricated monocrystalline Si/β-Ga2O3p–n heterojunctions, of which the characteristics were systematically studied. The heterojunctions demonstrated a diode rectification over 1.3 × 107 at ±2 V with a diode ideality factor of 1.13. Furthermore, capacitance–voltage (C–V) measurement showed frequency dispersion-free characteristics from 10 to 900 kHz. The interface defect density (Dit) was calculated as 1–3 × 1012/cm2 eV. Scanning transmission electron microscopy (STEM) and x-ray photoelectron spectroscopy (XPS) revealed that an ultrathin oxygen-rich layer existed on the Ga2O3 surface and later formed an ultrathin interfacial layer after bonding with Si. It is speculated that the excessive oxygen at the Ga2O3 surface enhanced the passivation of the Si dangling bonds and thus reduced Dit. This work improved our understanding of interface properties of the semiconductor grafting approach, providing useful guidance on the future development of Si/Ga2O3 heterojunction devices.

P‐156: Efficiency Improvement Mechanism Analysis of Sidewall Passivation GaN based Micro‐LEDs by Atomic Layer Deposition

Sidewall passivation using atomic layer deposition (ALD) can efficiently improve external quantum efficiency (EQE). Such treatment increases EQE, a combination of internal quantum efficiency (IQE) and light extraction efficiency (LEE), primarily by curtailing surface recombination according to the ABC model. Determined by the ratio of radiative recombination rate to total recombination rate, the IQE of an LED holds a significant correlation with the diode's ideality factor in the Shockley model. In this paper, we analysis the mechanism of ALD sidewall passivation enhancing device performance in detail from the aspects of electrical performance improvement and optical performance improvement.

Dually boosting the performance of photovoltaic module via integrating elastocaloric cooler

Photovoltaic module (PVM) only can utilize visible and ultra-violet parts of solar spectrum, constrained by the Shockley-Queisser limit. To fully use solar spectrum, in this study, solar selective absorber (SSA) and elastocaloric cooler (ECC) are gradually hybridized with PVM to form a new hybrid system for the first time. The performance metrics of PVM, ECC, and hybrid system, taking into account various irreversible effects, are mathematically derived. The hybrid system achieves approximately a 63% enhancement in both energy efficiency and power output density compared to a standalone PVM, outperforming other similar PVM-based hybrid systems. Exhaustive parametric studies show that increasing the operating temperature, solar irradiance, diode ideality factor, length ratio or section area ratio can enhance the hybrid system performance. The optimal combination of refrigerant and actuator materials are, respectively, Ni–Ti and Cu–Zn–Al alloys. Furthermore, a case study conducted to forecast practical performance under southeast China's weather conditions reveals that the hybrid system attains significant annual maximum energy efficiency and power output density, reaching 29.3% and 54.66 W m−2, respectively. The findings from this study provide valuable insights and recommendations for the optimum design and operation for such a hybrid system.

Low-temperature electrical properties and barrier inhomogeneities in ITO/β-Ga2O3 Schottky diode

This study reports the electronic properties of the indium tin oxide (ITO)/β-Ga2O3 Schottky diode through the temperature (50–320 K)-dependent current density–voltage, capacitance–voltage, and admittance spectroscopy experiments. The room-temperature turn-on voltage of the ITO/β-Ga2O3 diode was observed to be 0.83 V, and it exhibited a slow increase with decreasing temperature. The ITO/β-Ga2O3 diode's ideality factor (n) varied from 3.92 to 1.05, and the zero-bias Schottky barrier height (φbo) varied from 0.31 to 1.28 eV. The temperature-dependent n and φbo indicate the spatial inhomogeneities of the potential barrier at the Ga2O3-ITO interface. We exploit the Gaussian distribution model to explain the Schottky barrier inhomogeneities, which could be associated with the defects observed by the admittance spectroscopy method.

Improvement of Efficiency in Kesterite Solar Cells by Intentionally Inserting a Thin MoS2 Layer into the Back Interface.

A Mo(S,Se)2 interfacial layer is formed inevitably and uncontrollably between the Mo electrode and Cu2ZnSn(S,Se)4 (CZTSSe) absorber during the selenization process, which significantly influences the performance of CZTSSe solar cells. In this work, an ultrathin MoS2 layer is intentionally inserted into Mo/CZTSSe to reduce the recombination and thus optimize the interface quality. It is revealed that the absorber exhibits a continuous and compact morphology with bigger grains and remarkably without pinholes across the surface or cross-sectional regions after MoS2 modification. Benefitting from this, the shunt resistance (RSh) of the device increased evidently from ∼395 to ∼634 Ω·cm2, and simultaneously, the reverse saturation current density (J0) realized an effective depression. As a result, the power conversion efficiency (PCE) of the MoS2-modified device reaches 9.64% via the optimization of the thickness of the MoS2 layer, indicating performance improvements with respect to the MoS2-free case. Furthermore, the main contribution to the performance improvement is derived and analyzed in detail from the increased RSh, decreased J0, and diode ideality factor. Our results suggest that the Mo/CZTSSe interface quality and performance of CZTSSe solar cells can be modulated and improved by appropriately designing and optimizing the thickness of the inserted MoS2 layer.

A study on the dark and illuminated operation of Al/Si3N4/p-Si Schottky photodiodes: optoelectronic insights

This work extensively investigates the operation of an Al/ Si3N4/p-Si Schottky-type photodiode under dark and varying illumination intensities. The photodiode is fabricated by employing the metal–organic chemical vapor deposition (MOCVD) method. A thorough electrical characterization is performed at room temperature, encompassing measurements of current–voltage (I–V), current–time (I–t), capacitance–time (C–t), and conductance time (G–t). The photodiode’s rectification factor and reverse bias area increased under illumination. The relationship between light power density, barrier height, and diode ideality factor is found. The study also found a strong correlation between light intensity and applied voltage on series resistance (Rs) and shunt resistance (Rsh). Rs values are calculated using Cheung’s functions, revealing the diode’s resistance behavior. The study also examines the photodiode’s photoconductivity and photoconductance, finding a non-linear relationship between photocurrent and illumination intensity, suggesting bimolecular recombination. Calculated photosensitivity (K), responsivity (R), and detectivity (D*) values show the device’s light response effectiveness, but efficiency decreases at higher illumination intensities. Transient experiments indicate stable and reproducible photocurrent characteristics, revealing photogenerated charge temporal evolution. This study provides a complete understanding of the Al/Si3N4/p-Si Schottky photodiode’s behavior under different illumination intensities. The findings advance optoelectronic device knowledge and enable their use in advanced technologies.

Critical role of dopant in NiOx hole transport layer for mitigating redox reactivity at NiOx/absorber interface in mixed cation perovskite solar cells.

Redox chemistry transpiring at the interface of NiOx hole transport layer (HTL) and perovskite absorber is a critical phenomenon leading to relatively low values of open circuit voltage (VOC) and fill factor (FF), in turn hampering the overall device performance and stability. In this work, for the first time, the hard acid electronic nature of vanadium (V) dopant in nickel oxide HTL is opportunely exploited to mitigate the undesirable Lewis acid-base reactions occurring at the HTL/mixed-cation perovskite interface. The findings of the study show that vanadium doping results in improved interfacial energetics along with decreased VOC loss, confirming that despite the increase in Ni3+/Ni2+ ratio with the vanadium dopant, the redox reaction catalyzed by Ni3+ ions is kept under check. Vanadium doping also aided in the realization of superior perovskite films with lower Urbach energy, which translated into one order increase in maximum photoinduced carrier generation rate per unit volume. Carrier dynamics investigations show fewer defect states (lower VTFL) and trap-assisted recombination (lower diode ideality factor), which optimize the devices' photovoltaic performance. These benefits collectively contribute to low-loss charge transfer across the NiOx/mixed-cation perovskite interface, which increases the relative efficiency by ∼30% for 5 wt% V-doped NiOx devices compared to pristine NiOx devices, augmented by an increase in device J-V parameters like open circuit voltage (VOC), short circuit current density (JSC), and fill factor (FF).

ANALYSIS OF PERFORMANCE OF A PV SOLAR CELL AND EFFECT OF PHYSICAL PARAMETER

In recent days, PV solar systems have been commercialized in almost the whole world because of its advantageous efforts like a long-term supply of power at a very lower cost and various governments are also encouraging consumers to use sustainable green energy. The purpose of this study was to develop a model that allows the user to predict PV cell’s current-voltage (I-V) and power-voltage (P-V) characteristic curves by varying irradiance, cell temperature, and diode ideality factor, and the value of series resistance. The characteristic curves obtained from the simulation of the MATLAB/Simulink model are matched with the data given by the manufacturers by changing the value of mentioned internal parameters. Comparative results of one and two diode models with different electrophysical parameters are shown. There are analyses for photocurrent, voltage and power, as well as their dependence on single and two diode models. Block diagram models for diodes are also presented. Keywords: Irradiance, Temperature, Ideality Factor, Series Resistance, current-voltage characteristics.

Fabrication of n-ZnS/p-SnS, n-ZnO/p-SnS, and n-SnO2/p-SnS heterojunctions by 2-step SILAR process for photodetector applications

In this work, we present the fabrication and detailed analysis of three functional heterojunctions based on SnS. Unlike most of the previous reports, all semiconductor layers in the heterojunctions were deposited using the low-cost SILAR technique. The ZnS, ZnO, and SnO2 films, each with a thickness of 400 nm, were grown on a previously deposited 800 nm SnS layer, forming n-ZnS/p-SnS, n-ZnO/p-SnS, and n-SnO2/p-SnS heterojunctions. Current-voltage characteristics confirmed the successful formation of p-n junctions. Various models were used to estimate junction parameters such as diode ideality factor, barrier height, and series resistance. The fabricated diodes exhibited a prominent photo response under illumination. Photodetection figures of merit were estimated for all the devices. n-ZnS/p-SnS showed 0.003μA response current, with 0.27 sensitivity. The responsivity observed was around 0.6 μA /W with LDR of 2.09 dB. The specific detectivity was 106 Jones. Similarly, n-ZnO/p-SnS showed 0.021μA response current, with 0.38 sensitivity. The responsivity observed was around 4.2 μA /W with LDR of 2.80 dB. The specific detectivity was 106 Jones. However, n-SnO2/p-SnS showed remarkable figures of merit such as 2.4 μA response current, with 8.40 sensitivity. The responsivity observed was around 488 μA/W with LDR of 19.47 dB. The specific detectivity was 109 Jones. The rise and decay time of the photocurrent were 5 and 7 s, respectively.

Investigation of fundamental electrical and optoelectronic properties of an organic- and carbon-based MnPc/GC photodiode with high photosensitivity

The aim of this work is to provide an alternative to optoelectronic devices that use carbon and organic materials. To achieve this, we coated a modified MnPc organic semiconductor compound onto a graphite-like carbon (GC) thin film using the thermal evaporation technique, and fabricated an organic-based, highly light-sensitive MnPc/GC hybrid heterojunction. The heterojunction had a transmittance of approximately 60% in the visible region, an absorption coefficient of ∼106 m−1, and an energy band gap of 2.6 eV. Subsequently, Ag contacts were grown on the surface of each layer, and the Ag/MnPc/GC/Ag photodiode was subjected to fundamental electrical analysis at various light intensities and a ±3 V applied potential. Analysis in a dark environment revealed that the photodiode had a rectification ratio of 2.59 × 103, a series resistance of 28 Ω, and a shunt resistance of 4.17 × 104 Ω, as calculated from Ohm’s law. The diode ideality factor and barrier height of the photodiode were determined from thermionic emission theory to be 5.60 and 0.71 eV, respectively, and it was observed that these decreased with increasing light intensity. The photodetector parameters of the MnPc/GC hybrid photodiode were determined under positive and negative applied potentials at various light intensities. The highest photocurrent, photoconductive responsivity, photosensitivity, and specific detectivity were determined to be 1.512 × 10−1 A, 11.52 A.W−1, 9.83 × 105, and 2.48 × 1012 Jones, respectively, which were significantly higher than those reported in literature for organic and inorganic-based photodiodes. Based on the findings, it was concluded that the Ag/MnPc/GC/Ag photodiode holds promise as an alternative for sensors, solar cells, photodetectors, and optoelectronic communications applications.

SnF2‐Doped Cs2SnI6 Ordered Vacancy Double Perovskite for Photovoltaic Applications

Air‐stable p‐type SnF2:Cs2SnI6 with a bandgap of 1.6 eV has been demonstrated as a promising material for Pb‐free halide perovskite solar cells. Crystalline Cs2SnI6 phase is obtained with CsI, SnI2, and SnF2 salts in gamma‐butyrolactone solvent, but not with dimethyl sulfoxide and N,N‐dimethylformamide solvents. Cs2SnI6 is found to be stable for at least 1000 h at 100 °C when dark annealed in nitrogen atmosphere. In this study, Cs2SnI6 has been used in a superstrate n–i–p planar device structure enabled by a spin‐coated absorber thickness of ≈2 μm on a chemical bath deposited Zn(O,S) electron transport layer. The best device power conversion efficiency reported here is 5.18% with VOC of 0.81 V, 9.28 mA cm−2 JSC, and 68% fill factor. The dark saturation current and diode ideality factor are estimated as 1.5 × 10−3 mA cm−2 and 2.18, respectively. The devices exhibit a high VOC deficit and low short‐circuit current density due to high bulk and interface recombination. Device efficiency can be expected to increase with improvement in material and interface quality, charge transport, and device engineering.

Innovative approaches to extract double-diode model physical parameters of a PV module serving outdoors under real-world conditions

This paper presents innovative techniques for modeling and simulating photovoltaic (PV) solar modules. The major objective is to determine the seven parameters of Double-Diode Model (DDM) for PV modules serving indoors under standard test conditions (STC), non-STC conditions, or outdoors under real-world conditions. The first method employs a precise iterative technique utilizing numerical variation of two diode ideality factors on a newly derived transcendental equation relating series resistance to ideality factors and PV measurements to find values of series resistance, parallel conductance, photocurrent and two diode saturation currents at STC. The second method utilizes a system of non-linear equations corresponding to key-points of current–voltage (I-V) curve and numerical values of seven parameters at STC to determine time dependent values of DDM physical parameters throughout an arbitrary day under real-world conditions. The third is a predictive approach based on analytical formulas portraying effects of solar irradiance and temperature on DDM physical parameters for PV modules installed at any location and serving during an arbitrary day. The proposed techniques are validated with actual data of four PV modules of polycrystalline silicon (poly-Si) and monocrystalline silicon (mono-Si) technologies from National Renewable Energy Laboratory (NREL) database. Absolute Error (AE) values for DDM parameter extraction method at STC do not exceed 5 μA. Normalized Root Mean Square Error (NRMSE) ceiling value is equal to 3 % for both numerical approach of extraction and analytical approach of prediction under real-word conditions. The results demonstrate the reliability of extracted DDM physical parameters and their compatibility with experimental I-V data, lending credibility to these methods for analyzing and optimizing PV systems.

The effect of ZnO:Si3N4 nanocomposite interlayer on electrical properties and interface-states between metal-semiconductor in Al/p-Si (MS) structures

In the study, the fabrication processes of the Al/p-Si (MS), Al/ZnO/p-Si (MIS1), and Al/(ZnO:Si3N4)/p-Si (MIS2) structures were described and the effect of the ZnO:Si3N4 interface layer in MS was investigated in detail. The ZnO and (ZnO:Si3N4) thin films were coated on p-Si substrates and annealed at 500 °C for 1 h. Si3N4 and ZnO phases were identified via X-ray diffraction (XRD) and Raman spectra. FESEM images demonstrated that ZnO nanorods grew on Si3N4 particles with a heterogeneous nucleation mechanism. The I–V characterization was performed in the dark (±4 V). The basic diode parameters (barrier height (BH), series/shunt (Rs/Rsh) resistances, rectifying rate (RR=If/Ir), and ideality factor (n)) were calculated from various methods. The RR, and Rsh values increased, but n, Rs and BH decreased by insulating layer in the MIS2 The energy-dependent profiles of interface-states (Nss) were also extracted from the I–V plots according to voltage-dependent n and BH. The MIS2 provided the best passivation effect with decreasing interface traps.

Five parameters extraction of single diode PV model by metaheuristic optimization method by identified built-up data

Precision calculation of unknown photovoltaic (PV) modules or single diode models for PV cell specifications under various environmental conditions is needed to build a sunlight-based PV framework. Installing a PV system requires knowledge of all parameters, modeling, and optimization techniques because PV system analysis and configuration help generate renewable energy. This concept requires accurate modeling and calculation of identified and unknown parameters. The single-diode model is simple and accurate for different mathematical equations. Streamlining calculations requires distinguishing this nonlinear model. The current investigation calculated five unknown parameters and compared them with particle swarm optimization (PSO) and wind-driven optimization (WDO) optimization results. The said approach utilizes MATLAB software, analytical as well as optimization methods, and manufacturing data. The suggested method is simple, fast, and accurate for calculating diode ideality factor (A), output currents (Io), series resistance (Rs), Shunt resistance (Rsh), and photocurrent (Iph).

Modeling, Simulation and Extraction of Model Parameters of Dye-Sensitized Solar Cells (DSSCs) using Different Single-Diode Models

Modeling, simulation and extraction of model parameters of four DSSCs was carried out using four different models. The results show that model parameters depend on of the types of models and dyes (or DSSCs). Also, the fewer the number of model parameters the lesser the computation efforts and knowledge about the internal features of the photovoltaic system and vice versa. In addition, the photocurrent Iph of a DSSC is constant for all models. Furthermore, the diode reverse saturation current Io is inversely proportional to the absolute values of the series resistance Rs and shunt resistance Rsh. Moreover, the modified diode ideality factor depends on the number of model parameters and nature of dye/DSSC. However, models with higher number of model parameters (4 and 5) involving resistances manifest parameter irregularity. Nevertheless, the negative sign or complexity of the model parameters does not render them undesirable elements for researchers to use them in their application. Thus, the overall result shows that all the models used produced good I-V curve fit for all the solar cells studied irrespective of the presence of parameter irregularity.Keywords: Modeling, Simulation, Model parameter, DSSCs, Single diode model, Parameter irregularity.

Experimental Confirmation of the Optoelectronic Reciprocity Theorem in High-Efficiency CuIn1−xGaxSe2 Solar Cells

The optoelectronic reciprocity theorem has been proposed as a theorem relating electroluminescence (EL) and photovoltaic external quantum efficiency in solar cells. The theorem is vital for a fundamental understanding of solar cell operation and its application to device evaluation. Furthermore, with this theorem, it is also possible to estimate the open-circuit voltage (${V}_{\mathrm{OC}}$) of solar cells using the external radiative efficiency (${\ensuremath{\eta}}_{\mathrm{ext}}$) obtained from the absolute value of EL emission intensity, even for solar cells for which we cannot directly measure ${V}_{\mathrm{OC}}$, such as subcells of multijunction solar cells or individual $\mathrm{Si}$ cells in modules and arrays. However, it is not a priori obvious that the optoelectronic reciprocity theorem holds for the various solar cells that exist. In this study, we report the results of qualitative and quantitative confirmation of the validity of the optoelectronic reciprocity theorem for high-efficiency ${\mathrm{Cu}\mathrm{In}}_{1\ensuremath{-}x}{\mathrm{Ga}}_{x}{\mathrm{Se}}_{2}$ (CIGS) solar cells fabricated by us. The results confirm that our CIGS solar cells qualitatively and quantitatively satisfy the optoelectronic reciprocity theorem within the limits of measurement uncertainty. Also, we experimentally confirm that the value of the diode ideality factor for the applied voltage dependence of the EL emission intensity is exactly unity when the emission mechanism is the band-edge emission due to the direct recombination of electron-hole pairs. Finally, the importance of the ${\ensuremath{\eta}}_{\mathrm{ext}}$ for improving solar cell efficiency is explained.