Semitransparent Organic Photovoltaics Research Articles

A relatively wide-bandgap and air-stable donor polymer for fabrication of efficient semitransparent and tandem organic photovoltaics

Organic photovoltaics (OPVs) have attracted tremendous attention in the field of thin-film solar cells due to their wide range of applications, especially for semitransparent devices. Here, we synthesize a dithiaindacenone-thiophene-benzothiadiazole-thiophene alternating donor copolymer named poly{[2,7-(5,5-didecyl-5H-1,8-dithia-as-indacenone)]-alt-[5,5-(5',6'-dioctyloxy-4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)]} (PDTIDTBT), which shows a relatively wide bandgap of 1.82 eV, good mobility, and high transmittance and ambient stability. In this work, we fabricate an OPV device using monolayer graphene as top electrode. Due to the stability of PDTIDTBT in air and water, we use a wet transfer technique for graphene to fabricate semitransparent OPVs. We demonstrate OPVs based on the PDTIDTBT:Phenyl-C61/71-butyric acid methyl ester (PCBM) blend with maximum power conversion efficiencies (PCEs) of 6.1 and 4.75% using silver and graphene top electrodes, respectively. Our graphene-based device shows a high average visible transmittance (AVT) of 55%, indicating the potential of PDTIDTBT for window application and tandem devices. Therefore, we also demonstrate tandem devices using the PDTIDTBT:Phenyl-C61-butyric acid methyl ester (PC60BM) blend in both series and parallel connections with average PCEs of 7.3 and 7.95%, respectively. We also achieve a good average PCE of 8.26% with an average open circuit voltage (Voc) of 1.79 V for 2-terminal tandem OPVs using this blend. Based on tandem design, an OPV with PCE of 6.45% and AVT of 38% is demonstrated. Moreover, our devices show improved shelf life and ultraviolet (UV) stability (using CdSe/ZnS core shell quantum dots [QDs]) in ambient with 45% relative humidity.

Enhanced Light Utilization in Semitransparent Organic Photovoltaics Using an Optical Outcoupling Architecture.

Building-integrated photovoltaics employing transparent photovoltaic cells on window panes provide an opportunity to convert solar energy to electricity rather than generating waste heat. Semitransparent organic photovoltaic cells (ST-OPVs) that utilize a nonfullerene acceptor-based near-infrared (NIR) absorbing ternary cell combined with a thin, semitransparent, high conductivity Cu-Ag alloy electrode are demonstrated. A combination of optical outcoupling and antireflection coatings leads to enhanced visible transmission, while reflecting the NIR back into the cell where it is absorbed. This combination of coatings results in doubling of the light utilization efficiency (LUE), which is equal to the product of the power conversion efficiency (PCE) and the average photopic transparency, compared with a conventional semitransparent cell lacking these coatings. A maximum LUE = 3.56 ± 0.11% is achieved for an ST-OPV with a PCE = 8.0 ± 0.2% at 1 sun, reference AM1.5G spectrum. Moreover, neutral colored ST-OPVs are also demonstrated, with LUE = 2.56 ± 0.2%, along with Commission Internationale d'Eclairage chromaticity coordinates of CIE = (0.337, 0.349) and a color rendering index of CRI = 87.

Environmental and economic impacts of solar‐powered integrated greenhouses

AbstractGreenhouse vegetable production plays a vital role in providing year‐round fresh vegetables to global markets, achieving higher yields, and using less water than open‐field systems, but at the expense of increased energy demand. This study examines the life cycle environmental and economic impacts of integrating semitransparent organic photovoltaics (OPVs) into greenhouse designs. We employ life cycle assessment to analyze six environmental impacts associated with producing greenhouse‐grown tomatoes in a Solar PoweRed INtegrated Greenhouse (SPRING) compared to conventional greenhouses with and without an adjacent solar photovoltaic array, across three distinct locations. The SPRING design produces significant reductions in environmental impacts, particularly in regions with high solar insolation and electricity‐intensive energy demands. For example, in Arizona, global warming potential values for a conventional, adjacent PV and SPRING greenhouse are found to be 3.71, 2.38, and 2.36 kg CO2 eq/kg tomato, respectively. Compared to a conventional greenhouse, the SPRING design may increase life cycle environmental burdens in colder regions because the shading effect of OPV increases heating demands. Our analysis shows that SPRING designs must maintain crop yields at levels similar to conventional greenhouses in order to be economically competitive. Assuming consistent crop yields, uncertainty analysis shows average net present cost of production across Arizona to be $3.43, $3.38, and $3.64 per kg of tomato for the conventional, adjacent PV and SPRING system, respectively.

Semi-transparent quaternary organic blends for advanced photovoltaic applications

In spite of enormous promise in a multitude of applications, semi-transparent organic photovoltaics (ST OPVs) relatively lag behind opaque OPVs in the efficiency, and further efforts are imperative to improve their performance while preserving their transparency and tunable color perceptivity. Here, we develop highly efficient ST OPVs based on quaternary blends (Q-blend) involving non-fullerene small molecules, and demonstrate their realistic application in four-terminal (4T) tandem PVs. The ST quaternary OPV (Q-OPV) exhibits superior power conversion efficiencies (PCEs) higher than those of the state-of-the-art ST OPVs under any irradiation conditions, while retaining high transparency and the possibility of implementing various colors. In particular, we achieve the first PCE value exceeding 15% (~15.46%) under indoor lighting among the ST OPVs reported to date. The 4T tandem configurations based on a ST Q-OPV with diverse opaque PVs demonstrate broadband photon harvesting, with aesthetic functions rendered from the color-codable ST Q-OPV. The benefits of the Q-blend platform, including efficient operation under any irradiation circumstance (both indoor and outdoor lighting) and device color codability via tuning the quaternary components, can further expand the applicability of the ST Q-OPV to various practical applications.

Interfacial engineering and optical coupling for multicolored semitransparent inverted organic photovoltaics with a record efficiency of over 12%

Guided by finite-difference time-domain (FDTD) and optical transfer matrix formalism (TMF) simulation, the contradiction between PCE and AVT was solved, and multicolored ST-OSCs with record high efficiency were achieved.

Organic Photovoltaics on Greenhouse Rooftops: Effects on Plant Growth

Abstract Greenhouse agriculture is a high-growth and high-volume market that rapidly expands worldwide to address the societal needs for food production. The increasing demand for energy to cover their requirements, coupled with the limited amount of available fossil fuels, has turned the agriculture community in the exploitation of renewable energy sources. Intensive research is currently focuses on the use of solar energy in agriculture constructions. Organic Photovoltaics (OPVs) are constantly gaining ground among other PV technologies due to their low weight, tunable optical transmittance, flexibility and high conformability. In this work, semi-transparent OPVs based on the blend of regioregular poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) were integrated on the rooftop of the 24 m2 experimental Mediterranean greenhouse covering the 22% of its total area in order to investigate its effect on the growth and behavior of cultivated pepper plants (Capsicum annuum). Under the shade of OPVs, the pepper plants produced 20.2% more fruit mass compared to the control ones. In addition, at the end of the growing season, the height of the shaded plants was 21.8% larger than the remaining plants.

Heat-Insulating Multifunctional Semitransparent Polymer Solar Cells

Summary Semitransparent organic photovoltaics (ST-OPVs) have attracted extensive attention due to their potential for integration into the windows of buildings. Herein, we propose a dual-functional ST-OPV device that is not only highly efficient but also very effective for heat insulation. By introducing non-fullerene acceptor with enhanced near-infrared absorption and distributed Bragg reflectors for selectively enhancing the transmittance in visible wavelengths while keeping high reflectance for near-infrared light, the ST-OPVs generate over 6% power conversion efficiency with high visible light transmission of over 25% and outstanding infrared radiation rejection rate of over 80%. Our results show that with proper design of ST-OPVs, they can be used not only for generating power from sunlight but also for solar shading and heat insulation, which opens up a new application of OPVs for both energy harvesting and saving.

Halide Perovskites for Selective Ultraviolet-Harvesting Transparent Photovoltaics

Summary Halide perovskite materials have emerged as a potential Si replacement with excellent photovoltaic properties. There has been growing interest in applying halide perovskites to semitransparent and spatially segmented transparent photovoltaics (TPVs) to enable a greater range of deployment routes. However, the continuous-band absorption of these semiconductors prevents near-infrared selective harvesting typically targeted for TPVs with the highest efficiency and transparency needed to meet the aesthetic demands of many potential applications. In this work, we demonstrate TPVs based on perovskite semiconductors where the band gap is sensitively tuned with a range of compositions to selectively harvest only ultraviolet photons with band gaps between 410 and 440 nm. This approach offers theoretical efficiencies up to 7% with >99% visible transparency when precisely targeting band gaps around 435 nm. Practical optimization of these perovskite cells could quickly yield TPVs with power conversion efficiencies rivaling state-of-the-art near-infrared harvesting TPVs today while also providing a route to higher-efficiency multi-junction TPVs.

Performance and stability of semitransparent OPVs for building integration: A benchmarking analysis

Semitransparent (ST) organic photovoltaics (OPVs) are demonstrating great potential for building integration applications, especially in windows. For that purpose, ST-OPVs should achieve adequate transparency and performance stability. In this regard, the present research deals with the experimental performance of three different building-integrated ST-OPV technologies (technology A: developed in the frame of the present study; technologies B and C: commercial modules). More specifically, spectral transmittance and electrical measurements have been conducted in order to determine the characteristics of the modules for building integration and electricity generation purposes. Results regarding the transmittance reveal that technology A outperforms technologies B and C. The stability analysis of the modules verifies that module C is the most stable one with almost no decrease (3.6%) in the power conversion efficiency (PCE). Furthermore, the PCE of technology B is slightly higher than in the case of technology C, which experiences a PCE degradation of about 10–15% over the whole time period. Finally, technology A presents a 20% reduction in PCE at around 500 h.

Microcavity Structure Provides High‐Performance (>8.1%) Semitransparent and Colorful Organic Photovoltaics

AbstractHigh‐performance colored aesthetic semitransparent organic photovoltaics (OPVs) featuring a silver/indium tin oxide/silver (Ag/ITO/Ag) microcavity structure are prepared. By precisely controlling the thickness of the ITO layer, OPV devices exhibiting high transparency and a wide and high‐purity color gamut are obtained: blue (B), green (G), yellow‐green (YG), yellow (Y), orange (O), and red (R). The power conversion efficiencies (PCEs) of the G, YG, and Y color devices are greater than 8% (AM 1.5G irradiation, 100 mW cm−2) with maximum transmittances (TMAX) of greater than 14.5%. An optimized PCE of 8.2% was obtained for the YG OPV [CIE 1931 coordinates: (0.364, 0.542)], with a value of TMAX of 17.3% (at 561 nm). As far as it is known, this performance is the highest ever reported for a transparent colorful OPV. Such high transparency and desired transmitted colors, which can perspective see the clear images, suggest great potential for use in building‐integrated photovoltaic applications.

Intrinsic coincident full-Stokes polarimeter using stacked organic photovoltaics.

An intrinsic coincident full-Stokes polarimeter is demonstrated by using strain-aligned polymer-based organic photovoltaics (OPVs) that can preferentially absorb certain polarized states of incident light. The photovoltaic-based polarimeter is capable of measuring four Stokes parameters by cascading four semitransparent OPVs in series along the same optical axis. This in-line polarimeter concept potentially ensures high temporal and spatial resolution with higher radiometric efficiency as compared to the existing polarimeter architecture. Two wave plates were incorporated into the system to modulate the S₃ Stokes parameter so as to reduce the condition number of the measurement matrix and maximize the measured signal-to-noise ratio. Radiometric calibration was carried out to determine the measurement matrix. The polarimeter presented in this paper demonstrated an average RMS error of 0.84% for reconstructed Stokes vectors after normalized to S₀. A theoretical analysis of the minimum condition number of the four-cell OPV design showed that for individually optimized OPV cells, a condition number of 2.4 is possible.

Self-Supplied Nano-Fusing and Transferring Metal Nanostructures via Surface Oxide Reduction.

Here, we demonstrate that chemical reduction of oxide layers on metal nanostructures fuses junctions at nanoscale to improve the opto-electrical performance, and to ensure environmental stability of the interconnected nanonetwork. In addition, the reducing reaction lowers the adhesion force between metal nanostructures and substrates, facilitating the detachment of them from substrates. Detached metal nanonetworks can be easily floated on water and transferred onto various substrates including hydrophobic, floppy, and curved surfaces. Utilizing the detached metal nanostructures, semitransparent organic photovoltaics is fabricated, presenting the applicability of proposed reduction treatment in the device applications.

Neutral-Color Semitransparent Organic Solar Cells with All-Graphene Electrodes.

Graphene has been considered as a promising material for transparent electrodes due to its advantages including ultrahigh carrier mobilities, high optical transmittance, excellent mechanical flexibility, and good stability. Solar cells with all-graphene electrodes are potentially low-cost, high-performance, and environmental friendly, which however have not been realized until now. Here, we report the fabrication of semitransparent organic photovoltaics (OPVs) with graphene transparent electrodes as both cathode and anode, which can absorb light from both sides with the power conversion efficiency up to 3.4%. Meanwhile, the OPVs have a neutral color and show the transmittance of ∼40% in the visible region, making them suitable for some special applications, such as power-generating windows and building integrated photovoltaics. This work demonstrates the great potential of graphene for the applications in carbon-based optoelectronic devices.

Role of vertical segregation in semitransparent organic photovoltaics.

In this work, the efficiency of semitransparent organic photovoltaic (OPV) devices for low intensity applications is investigated as a function of the processing conditions. It is observed that a thermal treatment of the organic layer induces fullerene migration toward the active layer/air interface. This physical process gives rise to different vertical segregation profiles of donor and acceptor molecules. Once the back contact is deposited, the amount of fullerene covering the surface will determine the contact selectivity and leakage current of the device. Control of this leakage current may not be essential for devices fabricated for high illumination condition applications. However, devices to be used under low illumination conditions may be highly influenced by the presence of this parasitic dark current which flows in the opposite direction to photogenerated current. At the proximity of the contacts, the vertical segregation profile is inferred from optical and electrical measurements. In particular, external quantum efficiency (EQE) measurements carried out from a relatively opaque back contact provide local information on the materials spatially close to the light source. Alternatively, capacitance-voltage measurements enable calculation of the percentage of fullerene molecules covering the cathode contact. Overall, a versatile method that can be used in regular and inverted configuration is presented that explains the different behavior observed for devices to be used under low illumination conditions.

Semi‐Transparent Polymer Solar Cells with Excellent Sub‐Bandgap Transmission for Third Generation Photovoltaics

Semi-transparent organic photovoltaics are of interest for a variety of photovoltaic applications, including solar windows and hybrid tandem photovoltaics. The figure shows a photograph of our semi-transparent solar cell, which has a power conversion efficiency of 5.0%, with an above bandgap transmission of 34% and a sub-bandgap transmission of 81%.

Semitransparent organic photovoltaics using a near-infrared absorbing cyanine dye

A selective near-infrared absorbing heptamethine cyanine dye (Cy7-P) electron donor was used for the fabrication of bilayer solar cells with the acceptor C60. Using a reflective metal top electrode, solar cell optimization resulted in an external power conversion efficiency (η) of 1.5% for layer thicknesses of ~20nm for Cy7-P and of ~40nm for C60, with using either PEDOT:PSS or MoO3 as anode and Alq3 as cathode buffer layers. Highly transparent devices were then fabricated by using silver/Alq3 cathodes. Average visible transmittance (450–670nm) values of, for example, 67.2% (η=0.7%), 62.1% (η=0.9%) or 50% (η=1%) were obtained for different thickness combinations of silver and Alq3. Optimized solar cells had a maximum transparency of 79.8% at 568nm. The operational stability under 1sun illumination was T80=30h, after which 80% of the initial cell performance was reached.

Thin Metal Electrodes for Semitransparent Organic Photovoltaics

We demonstrate semitransparent organic photovoltaics (OPVs) based on thin metal electrodes and polymer photoactive layers consisting of poly(3-hexylthiophene) and [6,6]-phenyl C61 butyric acid methyl ester. The power conversion efficiency of a semitransparent OPV device comprising a 15-nm silver (Ag) rear electrode is 1.98% under AM 1.5-G illumination through the indium-tin-oxide side of the front anode at 100 mW/cm2 with 15.6% average transmittance of the entire cell in the visible wavelength range. As its thickness increases, a thin Ag electrode mainly influences the enhancement of the short circuit current density and fill factor. Its relatively low absorption intensity makes a Ag thin film a viable option for semitransparent electrodes compatible with organic layers.

High-Performance Semitransparent Bulk-Heterojunction Organic Photovoltaics with Ag Interfacial Layer

Semitransparent bulk-heterojunction organic photovoltaics with power conversion efficiency (PCE) of 1.63±0.39% was achieved by using poly(3-hexylthiophene) (P3HT)/phenyl-C61-butyric acid methyl ester (PCBM) active layer and Ag/Ca/Ag transparent cathode. Insertion of a thin Ag interfacial layer (1 nm) between the P3HT/PCBM active layer and Ca/Ag transparent cathode dramatically improved the PCE from 0.83±0.33 to 1.63±0.39% as well as other photovoltaic properties such as fill factor, short-circuit current, and series resistance. In this experiment, it is considered that the improved device performance is possibly due to improved contact property by the Ag interfacial layer at the active/cathode interface.

High-Performance Semitransparent Bulk-Heterojunction Organic Photovoltaics with Ag Interfacial Layer

Semitransparent bulk-heterojunction organic photovoltaics with power conversion efficiency (PCE) of 1.63±0.39% was achieved by using poly(3-hexylthiophene) (P3HT)/phenyl-C61-butyric acid methyl ester (PCBM) active layer and Ag/Ca/Ag transparent cathode. Insertion of a thin Ag interfacial layer (1 nm) between the P3HT/PCBM active layer and Ca/Ag transparent cathode dramatically improved the PCE from 0.83±0.33 to 1.63±0.39% as well as other photovoltaic properties such as fill factor, short-circuit current, and series resistance. In this experiment, it is considered that the improved device performance is possibly due to improved contact property by the Ag interfacial layer at the active/cathode interface.