Semitransparent Photovoltaics Research Articles

Active heating of greenhouse integrated semitransparent photovoltaic thermal system with series connected semitransparent photovoltaic thermal air collectors

In order to fulfill the demand of energy and food security, active heating of controlled environment greenhouse integrated semitransparent photovoltaic thermal (GiSPVT) system with N-semitransparent photovoltaic thermal (SPVT) air collector for cold climatic condition has been analyzed in this paper. The proposed SPVT air collectors are connected in series and integrated with GiSPVT. It is used to generate thermal as well electrical energy to meet daily requirement of users. Based on energy balance equation which is a function of design and climatic parameters, an analytical expression for various variable parameters namely plant, room air and solar cell temperatures have been derived. Numerical computation has been made in Matlab for computing thermal, electrical and overall exergy of the proposed system. Based on numerical computation, the following observations have been made: (i) From thermal point of view, the packing factor (0.5, 0.8) of semitransparent PV module plays an important role and it has to be optimized for maximum thermal heating. (ii) The selection of number of collector N is an important parameter to generate electrical energy as well as thermal heating of GiSPVT room air in an optimum way.

Semitransparent organic photovoltaics enabled by transparent p-type inorganic semiconductor and near-infrared acceptor

Semitransparent organic photovoltaics (STOPVs) have gained wide attention owing to their promising applications in building-integrated photovoltaics, agrivoltaics, and floating photovoltaics. Organic semiconductors with high charge carrier mobility usually have planar and conjugated structures, thereby showing strong absorption in visible region. In this work, a new concept of incorporating transparent inorganic semiconductors is proposed for high-performance STOPVs. Copper(I) thiocyanate (CuSCN) is a visible-transparent inorganic semiconductor with an ionization potential of 5.45 eV and high hole mobility. The transparency of CuSCN benefits high average visible transmittance (AVT) of STOPVs. The energy levels of CuSCN as donor match those of near-infrared small molecule acceptor BTP-eC9, and the formed heterojunction exhibits an ability of exciton dissociation. High mobility of CuSCN contributes to a more favorable charge transport channel and suppresses charge recombination. The control STOPVs based on PM6/BTP-eC9 exhibit an AVT of 19.0% with a power conversion efficiency (PCE) of 12.7%. Partial replacement of PM6 with CuSCN leads to a 63% increase in transmittance, resulting in a higher AVT of 30.9% and a comparable PCE of 10.8%.

Reliability of colorfast semitransparent organic photovoltaics

Reliability of colorfast semitransparent organic photovoltaics

Experimental and simulation study on the thermoelectric performance of semi-transparent crystalline silicon photovoltaic curtain walls

This study aims to evaluate and optimize the thermoelectric performance of semi-transparent crystalline silicon photovoltaic (PV) curtain walls. An integrated thermoelectric performance coupling calculation model was developed, combining heat transfer and electricity generation calculations as a novel approach. Simulations and experiments were conducted to compare the performance of PV curtain walls with conventional curtain walls under various weather conditions, and were validated by experimental data. The results demonstrate that PV curtain walls enhance the thermal environment inside buildings and promote efficient power generation, with the arrangement of PV cells notably affecting performance. Under sunny conditions, the temperatures of the PV cell backplate and glass part backsheet in semi-transparent PV curtain walls exceeded those in ordinary glass curtain walls, yet the indoor air temperature was lower. Furthermore, when the working temperature of PV cells reaches to a certain level, it slightly deviates the electricity generation trend from the real-time solar radiation trend. Under cloudy conditions, the backsheet temperatures of semi-transparent PV curtain walls and standard glass curtain walls align with outdoor temperatures. Different PV module forms demonstrated that striped and square PV module forms offer better lighting effects than whole forms. The working temperatures among the three were close, with an annual average temperature difference of less than 1 °C and a peak temperature difference of approximately 3 °C, impacting the monthly total power generation by less than 1 %. This study presents a more precise and thorough approach for evaluating semi-transparent PV curtain walls' performance, providing insights for future sustainable architectural design.

Unveiling the Potential of Two-Terminal Perovskite/Organic Tandem Solar Cells: Mechanisms, Status, and Challenges.

Perovskite/organic tandem solar cells (PO-TSCs) demonstrate exceptional suitability for emerging applications such as building-integrated photovoltaics, wearable devices, and greenhouse farming. By leveraging the distinctive attributes of perovskite and organic materials, which encompass expanded solar spectrum utilization, chemically benign solubility, and soft nature, PO-TSCs position themselves as ideal candidates for high-performance semi-transparent photovoltaics (ST-PVs). Despite these advantages, their development significantly lags behind other perovskite-based counterparts, such as perovskite/perovskite, perovskite/silicon, and perovskite/Cu(In, Ga)Se2. To address existing challenges and unlock the full potential of PO-TSCs, an exploration of the fundamental mechanisms governing tandem photovoltaic devices is embarked. Delving into critical aspects such as charge generation/separation, energy level alignment, and material choices becomes pivotal for optimizing PO-TSC performance. The investigation of monolithic two-terminal PO-TSCs offers insights into achievements and barriers, recognizing the competitive landscape with other TSC counterparts. Further scrutiny of perovskite absorbers and organic absorbers in TSCs reveals strategies aimed at enhancing stability and efficiency. The discussion extends to interconnection layers, elucidating their role in optimizing light transmission and balancing carrier recombination. In conclusion, a compelling outlook on the dynamic landscape of PO-TSCs is presented, highlighting the remarkable efficiency progression and signaling their potential to revolutionize solar energy harvesting technologies.

Optical design and bandgap engineering in ultrathin multiple quantum well solar cell featuring photonic nanocavity

AbstractUltrathin solar cells are efficient and captivating devices with unique technological and scientific features in terms of minimal material consumption, fast fabrication processes, and good compatibility with semi‐transparent applications. Such photovoltaic (PV) technologies can enable effective synergy between optical and electronic confinements with large tuning capabilities of all the optoelectronic characteristics. In this work, the implications of the optical design and the bandgap engineering in ultrathin hydrogenated amorphous Si/Ge multiple quantum well (MQW) solar cells featuring photonic nanocavity are analyzed based on experimental measurements and optoelectronic modelling. By changing the period thicknesses and the positions of QWs inside the deep‐subwavelength nanophotonic resonator, the spatial and spectral distributions of the optical field and the local absorption are strongly affected. This leads to a modulation of the absorption resonance condition, the absorption edge and the resulting photocurrent outputs. Because of quantum confinement effect, the change of MQW configurations with different individual QW periods while keeping similar total thickness of about 20 nm alters both the bandgap energy and the band offset at the QW/barrier heterojunctions. This in turn controls the photovoltage as well as the carrier collection efficiency in solar cells. The highest open circuit voltage and fill factor values are achieved by employing MQW device configuration with 2.5 nm‐thin QWs. A record efficiency above 5.5% is reached for such emerging ultrathin Si/Ge MQW solar cell technology using thinner QWs with sufficient number, because of the optimum trade‐off between all the optoelectronic characteristic outputs. The presented design rules for opaque ultrathin solar cells with quantum‐confined nanostructures integrated in a photonic nanocavity can be generalized for the engineering of relevant multifunctional semitransparent PV devices.

Examining the effect of different photovoltaic modules on cucumber crops in a greenhouse agrivoltaic system: A case study

Agrivoltaic systems, a fusion of agriculture and photovoltaic (PV) technology, have emerged as a sustainable solution to optimise land use by enabling simultaneous solar energy and agricultural harvesting. The experiments were conducted in a polytunnel greenhouse in Kfar Qara, Israel, deploying three types of semi-transparent solar PV panels—bifacial glass-encapsulated silicon, bifacial plastic-encapsulated silicon, and semi-transparent organic photovoltaics (OPVs) installed above the plant canopy. The impact of these PV treatments on cucumber crops was evaluated and juxtaposed against a control greenhouse with no panels, over the spring season from February to June 2022. Key growth and yield metrics were recorded during 17 harvests between April 10 and June 2, 2022. The findings revealed a negligible decline in crop yield across PV panel treatments compared to the control. Notably, the control and glass-encapsulated silicon PV treatments demonstrated an increase in yield, growth, and fruit quality. Moreover, the glass-encapsulated silicon PV panels outperformed the plastic-encapsulated and OPV module power conversion in the high heat and humidity of the greenhouse environment. This study accentuates the potential of integrating glass-encapsulated silicon PV panels in polytunnel greenhouses, heralding a promising avenue for bolstering agrivoltaic applications by ensuring a harmonious balance between agricultural yield and electrical energy production.

Doping with KBr to Achieve High-Performance CsPbBr3 Semitransparent Perovskite Solar Cells.

Wide-bandgap semitransparent perovskite photovoltaics are emerging as one of the ideal candidates for building-integrated photovoltaics (BIPV). However, surface defects in inorganic CsPbBr3 perovskite prepared by vapor deposition severely limit the optoelectronic performance of perovskite solar cells. To address this issue, a strategy of doping a trace amount of KBr into perovskite by vapor deposition is adopted, effectively improving the quality of the film, reducing surface defect concentration, and enhancing the transportation and extraction of charge carriers. Simultaneously, fully physical vapor deposition technology is employed to fabricate perovskite solar cells with an average visible light transmittance of 44%. These devices exhibited an ultrahigh open-circuit voltage of 1.55 V and a superior power conversion efficiency (PCE) of 7.28%, demonstrating excellent moisture and heat resistance. Moreover, the corresponding 5 cm × 5 cm modules achieve a PCE of 5.35% with great thermal insulation capability. This work provides an approach for fabricating highly efficient all-inorganic perovskite solar cells with high average visible light transmittance, demonstrating new insights into their application in building-integrated photovoltaics.

Comprehensive performance investigation of a novel thermal catalytic semi-transparent PV double-skin ventilated window integrated with CdTe cells

Human health is adversely impacted by indoor formaldehyde. Given that buildings with conventional PV-DSVs fail to improve indoor air quality in the indoor or outdoor air circulation mode without any air handling devices. To remove indoor formaldehyde, a thermal-catalytic CdTe PV double-skin ventilated window is proposed. A corresponding mathematical model was established and validated against experiment data. Based on the validated model, the thermal, electrical, daylighting, and formaldehyde degradation performances were investigated and compared with a conventional PV-DSV (PV-CDSV). Additionally, parametric analysis was conducted to analyse impacts of four factors, including the area of catalytic coating, the window-to-wall ratio, outdoor solar radiation, and ambient temperature, on the energy performance of the proposed window. Main results are: (1) The proposed window had a higher power output but a bit lower thermal efficiency than PV-CDSV, and it had a higher ηtotal in winter, which reached 35.35 % and was 31.45 % higher than that of the PV-CDSV. (2) The net energy consumption of PV-TCDSV increased by 6.59 % and 6.26 % compared with PV-CDSV in winter and summer, respectively. (3) Among the four influencing factors, the solar radiation and ambient temperature had strong impacts on the effectiveness of formaldehyde degradation.

Semi-Transparent PV and Double-Glazed Windows for Heat Reduction and Electricity Generation: A Study for Office Buildings in Tropical Climate

This research aims to develop a methodology for the evaluation of the potential energy saving and energy generation of semi-transparent PV and double-glazed window in Indonesia office buildings. The evaluation is based on Comsol software. The heat transfer equations for the inside the enclosure between the glass have been constructed according to the natural convection equation. The simulations were accomplished for four orientations from January until December and compared to a single-glazed window. The results show that it is possible to reduce the energy consumption for artificial lighting and air-conditioning using appropriate control systems and furthermore to generate electricity using semi-transparent photovoltaic panels in windows. The use of semi-transparent PV and double-glazed window has proven to be more effective in reducing heat transfer in buildings and generate electricity. East-facing double-glazed windows produce the most electricity, approximately 341 kWh.

Economic and Performance Analysis of Modified Solar Distillation System Coupling Different Integrations Using Carbon Quantum Dot Nanoparticles: Generalized Thermal Model

Abstract Clean drinking water and electricity production utilizing non-conventional sources of energy is the global demand for sustainable development. Ultrafast heat transfer fluids have delivered impressive results in photovoltaic (PV)-integrated solar thermal systems, in recent times. Efforts have been made for the productivity and electricity augmentation of solar still equipped with helically coilled heat exchanger and coupled with different integrations, viz., (a) partially covered N-photovoltaic thermal compound parabolic concentrator (N-PVT-CPC), (b) partially covered N-photovoltaic thermal flat plate collector (N-PVT-FPC), (c) N-FPC-CPC, and (d) N-flat plate collector (N-FPC). System design has also been modified by adding a roof-top semi-transparent PV module and built-in passive copper condenser (circulation mode), and effect of carbon quantum dots (CQDs) water-based nanofluids, nanoparticles volume concentration, and packing factor (βc) of the PV module has been studied by developing generalized thermal modeling of the system (special cases). Overall, 41.1%, 21.52%, 22.01%, and 10.01% rise in evaporative HTCs is observed in FPC-CPC, PVT-CPC, FPC, and PVT-FPC integrations, respectively. Thermal exergy is found to be higher for FPC-CPC integration, and it follows the enhancement order as FPC-CPC (max-0.147 kW) > PVT-CPC (0.088 kW) > FPC (0.038 kW) > PVT-FPC (0.028 kW). In reference to the base fluid, significant enhancement in the daily productivity is observed for FPC-CPC (10.9%) and PVT-CPC (5.16%) integrations using CQD-NPs. The production cost of potable water has also been estimated for all the cases for n = 30 and n = 50 years life span and i = 4% and 8% interest rates, and it is found to be the lowest (0.014 $/L) for FPC-CPC integration using CQD-NPs (n = 30 years, i = 4%).

Low-damage hydrogen-doped transparent electrodes towards semitransparent perovskite photovoltaics

As one kind of transparent conductive electrodes (TCEs), transparent conductive oxides (TCOs) have been widely used in perovskite solar cells (PSCs). However, the conventional magnetron sputtering usually causes high-energy particles, thus damaging the underlying functional films and deteriorating the performance of devices. Therefore, developing a low-damage method for high-quality TCO film is crucial. Here, the hydrogen and cerium co-doped indium oxide (ICO:H) films were prepared by the reactive plasma deposition (RPD) technology at room temperature. Benefiting from the hydrogen doping, the bandgap of the ICO:H film was tuned to 3.97 eV, the average transmittances reached 91.25% (from 800 nm to 1200 nm) and 81.35% (from 300 nm to 800 nm), and the carrier mobility exceeded 30 cm2/V/s. Combined with these advantages, semitransparent perovskite solar cells (ST-PSCs) without buffer layers were fabricated using ICO:H films as transparent conductive window layers, and the power conversion efficiency (PCE) was up to 17.61% (from the glass side). Furthermore, the ICO:H films were also applied in two-terminal perovskite/silicon tandem solar cells, and the PCE exceeded 25%. This low-damage method opens a new avenue for fabricating film-based optoelectronics.

Growth and Physiological Characteristics of Strawberry Plants Cultivated under Greenhouse-Integrated Semi-Transparent Photovoltaics.

The integration of semi-transparent photovoltaics into the roof of greenhouses is an emerging technique used in recent years, due to the simultaneous energy and food production from the same piece of land. Although shading in many cases is a solution to maintain the desired microclimate, in the case of photovoltaic installations, the permanent shading of the crop is a challenge, due to the importance of light to the growth, morphogenesis, and other critical physiological processes. In this study, the effect of shade from semi-transparent photovoltaics on a strawberry crop (Fragaria x ananassa Duch.) was examined, in terms of growth and quality (phenolic and flavonoid concentration of fruits). According to the results, in non-shaded plants, there was a trend of larger plants, but without a significant change in leaf number, while the total number of flowers was slightly higher at the end of the cultivation period. Moreover, it was found that the percentage change between the number of ripe fruits was smaller than that of the corresponding change in fruit weight, implying the increased size of the fruits in non-shaded plants. Finally, regarding the antioxidant capacity, it was clearly demonstrated that shading increased the total phenolic content, as well as the free-radical-scavenging activity of the harvested fruits. Although the shading from the semi-transparent photovoltaics did not assist the production of large fruits, it did not affect their number and increased some of their quality characteristics. In addition, the advantageous impact of the semi-transparent photovoltaics in the energy part must not be neglected.

Identifying and Amplifying the Spontaneously Formed Photo‐Charge Contribution in Opaque and Semitransparent Organic Photovoltaics

AbstractSpontaneous photo‐charge (SP) generation within the non‐fullerene (NFA) bulk helps avoid exciton (EX) related loss as compared to the traditional heterojunction route in organic solar cells (OSCs). Unfortunately, the promising SP utilization attracts little attention at this time due to the lack of knowledge on its specific contribution to the photovoltaic performance and rational optimization in high‐efficiency devices. To fill the gap, the NFAs’ SP characteristics are related with their photocurrent loss and power conversion efficiency (PCE) in state‐of‐the‐art materials. Though higher SP population is good for efficient EX utilization, it simultaneously acts as an additional photo‐charge recombination channel. The former can be further enhanced by increasing the NFAs’ crystallinity with preferred lamellar growth, and the latter can be suppressed via electric doping. With the aid of the two‐step optimization strategy, the total photocurrent loss is reduced from 14.4% to 4.8%, accompanying with PCE increment from 16.9% to 18.5%. The SP utilization strategy is finally applied in the semitransparent OSCs (ST‐OSCs), due to its less heterojunction area sensitive photo‐charge generation characteristic. A light utilization efficiency (LUE) is then increased from 3.21% to 3.77%. The findings highlight the pursue of efficient SP utilization as a new design philosophy in future OSCs’ progresses.

Hot-Antisolvent Assisted Morphological Regulation of Perovskites for Semitransparent Photovoltaics Employing Hot-Pressing Approach

The processing of halide perovskites in the air significantly influences their morphology and surface coverage, often leading to the presence of numerous trap densities that adversely affect device performance. In this study, we explored the development of perovskite films using a solvent extraction method, where the temperature of the anisole antisolvent was varied. Our findings demonstrate that the hot-antisolvent strategy effectively controls nucleation, resulting in the formation of highly dense, pinhole-free, and crack-free perovskite films with reduced surface roughness. Films fabricated using this hot-antisolvent approach exhibited enhanced photoluminescence, indicating lower trap density and increased recombination resistance. They also showed slower charge carrier recombination rates and efficient charge extraction, suggesting the suppression of nonradiative recombination. Furthermore, the superior quality of perovskite films obtained through the hot-antisolvent strategy significantly enhanced the power conversion efficiency (PCE) of hot-pressed semitransparent perovskite solar cells. The PCE remarkably increased from 0.13% to an impressive 12.65% while maintaining an average visible transmittance of 26.55% and exceptional air stability for 2000 hours with no significant degradation in initial PCE. This study achieves a record-breaking light utilization efficiency of 3.36% in the realm of research on hot-press processes.

Luminous Transmittance and Color Rendering Characteristics of Evaporated Chalcopyrite Thin Films for Semitransparent Photovoltaics

The luminous transmittance and the color rendering index of daylight through semitransparent photovoltaic glazing are essential parameters for visual comfort indoors, and they must be considered for different absorber materials that were traditionally developed for opaque solar cells, such as those of the chalcopyrite type. With this aim, various chalcopyrite compounds (CuInSe2, CuInS2 and CuGaS2) were prepared by means of evaporation and then measured to obtain their optical absorption spectra. These experimental data are used here to calculate the solar absorptance (αS), luminous transmittance (τL) and color rendering index (Ra) as a function of the chalcopyrite film thickness. The comparative analysis of the different factors indicates that 70 nm thick CuInSe2 is optimal to guarantee excellent visual comfort (τL = 50% and Ra = 93%) while absorbing as much solar irradiance (αS = 37%) as 130 nm thick CuInS2 or 900 nm thick CuGaS2. The second option (130 nm thick CuInS2) is also considered good (τL = 40% and Ra = 80%), but for CuGaS2, the thickness should be kept below 250 nm in order to obtain a suitable color rendering Ra ≥ 60%.

Boosting the Performances of Semitransparent Organic Photovoltaics via Synergetic Near-Infrared Light Management.

Semitransparent organic photovoltaics (ST-OPVs) offer promising prospects for application in building-integrated photovoltaic systems and greenhouses, but further improvement of their performance faces a delicate trade-off between the two competing indexes of power conversion efficiency (PCE) and average visible transmittance (AVT). Herein, the authors take advantage of coupling plasmonics with the optical design of ST-OPVs to enhance near-infrared absorption and hence simultaneously improve efficiency and visible transparency to the maximum extent. By integrating core-bishell PdCu@Au@SiO2 nanotripods that act as optically isotropic Lambertian sources with near-infrared-customized localized surface plasmon resonance in an optimal ternary PM6:BTP-eC9:L8-BO-based ST-OPV, it is shown that their interplay with a multilayer optical coupling layer, consisting of ZnS(130nm)/Na3AlF6(60nm)/WO3(100nm)/LaF3(50nm) identified from high-throughput optical screening, leads to a record-high PCE of 16.14% (certified as 15.90%) along with an excellent AVT of 33.02%. The strong enhancement of the light utilization efficiency by ≈50% as compared to the counterpart device without optical engineering provides an encouraging and universal pathway for promoting breakthroughs in ST-OPVs from meticulous optical design.

New Nanophotonics Approaches for Enhancing the Efficiency and Stability of Perovskite Solar Cells.

Over the past decade, the power conversion efficiency (PCE) of perovskite solar cells (PSCs) has experienced a remarkable ascent, soaring from 3.8% in 2009 to a remarkable record of 26.1% in 2023. Many recent approaches for improving PSC performance employ nanophotonic technologies, from light harvesting and thermal management to the manipulation of charge carrier dynamics. Plasmonic nanoparticles and arrayed dielectric nanostructures have been applied to tailor the light absorption, scattering, and conversion, as well as the heat dissipation within PSCs to improve their PCE and operational stability. In this review, it is begin with a concise introduction to define the realm of nanophotonics by focusing on the nanoscale interactions between light and surface plasmons or dielectric photonic structures. Prevailing strategies that utilize resonance-enhanced light-matter interactions for boosting the PCE and stability of PSCs from light trapping, carrier transportation, and thermal management perspectives are then elaborated, and the resultant practical applications, such as semitransparent photovoltaics, colored PSCs, and smart perovskite windows are discussed. Finally, the state-of-the-art nanophotonic paradigms in PSCs are reviewed, and the benefits of these approaches in improving the aesthetic effects and energy-saving character of PSC-integrated buildings are highlighted.

High‐Performance Organic Photovoltaics Incorporating Bulk Heterojunction and p–i–n Active Layer Structures

In the past five years, significant advancements in the development of novel conjugated polymer donors (D) and non‐fullerene acceptors (A), such as small molecules, have substantially boosted the power conversion efficiency of bulk heterojunction (BHJ) organic photovoltaics (OPVs) devices to over 19%. Recently, in the pursuit of broader impact and heightened efficiency for OPVs, an alternative processing approach has emerged; this approach involves a sequential deposition (SD) technique or a layer‐by‐layer method, creating active layers with p–i–n structures (p and n stand for D and A region, respectively; i stands for BHJ region). Notably, this SD method is particularly effective in semitransparent organic photovoltaics (ST‐OPVs), despite the material requirements it entails. SD‐processing methods enable the creation of vertical multiple junctions and controllable D/A interfaces, facilitating exciton dissociation and charge transport through a well‐designed pseudo p–i–n structure. Furthermore, ST‐OPVs can be integrated into building‐incorporated photovoltaic modules, offering potential applications in greenhouses and agricultural modernization. This integration allows for the comprehensive utilization of solar spectrum energy. In this review, current literature is consolidated on new materials, such as conjugated polymers and non‐fullerene small molecules as electron‐donating and electron‐withdrawing materials, aimed at high‐efficiency OPVs and ST‐OPVs with BHJ‐ and p–i–n structured active layers, and perspectives are offered for future developments.

The Next Frontier of Solar Energy: Transparent Photovoltaics

The development of "Transparent Photovoltaics" (TPVs[1]), i.e., solar cells that are transparent to visible light, has become more and more popular in recent years due to their contribution to low CO2 emissions through "window power generation" in fully glazed buildings (building-integrated photovoltaics: BIPV) and the growing demand for development in the promotion of farm-based solar power; Agrivoltaics [2, 3]. So far, selective light-transmission photovoltaics (SLTPVs), in which conventional bulk and thin-film solar cells are fabricated into long and thin strips and arranged like a window shade at intervals or by reducing the film thickness, have already been put into practical use [3, 4], allowing part of the incident light to escape to the rear. However, the installation applications of SLTPVs are limited since blocking the line of sight outside the window and preventing a sufficient amount of light from reaching the interior or farmland surface. If TPVs that are uniformly transparent or tinted-transparent like window glasses can be commercialized, the range of applications is expected to expand significantly.TPVs are perceived by humans as being "nearly colorless" if they have a visible light transmittance of 80% or more, including the substrate material. Depending on the application, it is possible to produce red, and dark colors by adjusting the material characteristics so that only the short wavelength side of the visible light wavelength range, the long wavelength side, or the entire wavelength range is uniformly absorbed [2, 3]. These visible light-transmissive solar cells with visible light transmittance of 80% or less are referred to as semitransparent photovoltaics (STPVs).It is crucial to consider the theoretical limiting efficiency (TLE) for the practical application of TPVs. Recent reports have simulated TLs for single-junction and multi-junction cells with optical absorption in the UV and NIR regions, yet not in the visible region [5]. The results demonstrate that practical conversion efficiencies of 11% and 21% can be obtained for single-junction and 16-junction cells respectively, with 80% visible transmission. The optimal band gap for cells with 100% Vis-EQE (an external quantum efficiency in the visible light range of 435 to 670 nm) is around 1.5 eV, while for cells with 0% Vis-EQE and full transmission in the visible region, the optimal Eg shifts to the lower energy side of 1.1 to 1.2 eV. To use only the UV region without using the NIR region, 2.8 to 3.0 eV or higher can be easily approached with existing technology.Transparent photovoltaic cells (TPVs) and semi-transparent photovoltaic cells (STPVs) developed to date can be broadly classified into the following four types of power generation methods: TPVs (1) Heterojunction and homojunction with 3.0 eV and more wide-gap semiconductors as generating layers [6-8].(2) Glass plate (+ wavelength conversion material) with Si solar cells installed on the end face of the glass plate to form a module [9]. STPVs (3) Increased visible light transmittance by wider-gap semiconductor materials (colored transparent type) [3].(4) SLTPVs [4].If TPV can be made more cost-effective, it can be applied to various applications such as low CO2 emissions in buildings, photovoltaic power generation for agriculture, no external power source required for electric bulletin boards, auxiliary power source for electric vehicles, and so on. Research and development are categorized into the above areas (1) through (4), with (1) through (3) in particular requiring basic research and development from a materials perspective. The number of groups involved in research and requests for practical applications is increasing, and accelerated progress is expected.