Semi-transparent polymer solar cells with excellent sub-bandgap transmission for third generation photovoltaics

High-Performance Semi-Transparent Perovskite Solar Cells with over 22% Visible Transparency: Pushing the Limit through MXene Interface Engineering

Semi-transparent perovskite solar cells (ST-PSCs) have attracted enormous attention recently due to their potential in building-integrated photovoltaic. To obtain adequate average visible transmittance (AVT), a thin perovskite is commonly employed in ST-PSCs. While the thinner perovskite layer has higher transparency, its light absorption efficiency is reduced, and the device shows lower power conversion efficiency (PCE). In this work, a combination of high-quality transparent conducting layers and surface engineering using 2D-MXene results in a superior PCE. In situ high-temperature X-ray diffraction provides direct evidence that the MXene interlayer retards the perovskite crystallization process and leads to larger perovskite grains with fewer grain boundaries, which are favorable for carrier transport. The interfacial carrier recombination is decreased due to fewer defects in the perovskite. Consequently, the current density of the devices with MXene increased significantly. Also, optimized indium tin oxide provides appreciable transparency and conductivity as the top electrode. The semi-transparent device with a PCE of 14.78% and AVT of over 26.7% (400-800 nm) was successfully obtained, outperforming most reported ST-PSCs. The unencapsulated device maintained 85.58% of its original efficiency after over 1000 h under ambient conditions. This work provides a new strategy to prepare high-efficiency ST-PSCs with remarkable AVT and extended stability.

Proposal and Design of Flexible All-Polymer/CIGS Tandem Solar Cell

Tandem solar cells (TSCs) have attracted prodigious attention for their high efficiency, which can surmount the Shockley-Queisser limit for single-junction solar cells. Flexible TSCs are lightweight and cost-effective, and are considered a promising approach for a wide range of applications. In this paper, a numerical model, based on TCAD simulation, is presented to assess the performance of a novel two-terminal (2T) all-polymer/CIGS TSC. To confirm the model, the obtained simulation results were compared with standalone fabricated all-polymer and CIGS single solar cells. Common properties of the polymer and CIGS complementary candidates are their non-toxicity and flexibility. The initial top all-polymer solar cell had a photoactive blend layer (PM7:PIDT), the optical bandgap of which was 1.76 eV, and the initial bottom cell had a photoactive CIGS layer, with a bandgap of 1.15 eV. The simulation was then carried out on the initially connected cells, revealing a power conversion efficiency (PCE) of 16.77%. Next, some optimization techniques were applied to enhance the tandem performance. Upon treating the band alignment, the PCE became 18.57%, while the optimization of polymer and CIGS thicknesses showed the best performance, reflected by a PCE of 22.73%. Moreover, it was found that the condition of current matching did not necessarily meet the maximum PCE condition, signifying the essential role of full optoelectronic simulations. All TCAD simulations were performed via an Atlas device simulator, where the light illumination was AM1.5G. The current study can offer design strategies and effective suggestions for flexible thin-film TSCs for potential applications in wearable electronics.

Green Energy by Hydrogen Production from Water Splitting, Water Oxidation Catalysis and Acceptorless Dehydrogenative Coupling

In this review, we want to explain how the burning of fossil fuels is pushing us towards green energy. Actually, for a long time, we have believed that everything is profitable, that resources are unlimited and there are no consequences. However, the reality is often disappointing. The use of non-renewable resources, the excessive waste production and the abandonment of the task of recycling has created a fragile thread that, once broken, may never restore itself. Metaphors aside, we are talking about our planet, the Earth, and its unique ability to host life, including ourselves. Our world has its balance; when the wind erodes a mountain, a beach appears, or when a fire devastates an area, eventually new life emerges from the ashes. However, humans have been distorting this balance for decades. Our evolving way of living has increased the number of resources that each person consumes, whether food, shelter, or energy; we have overworked everything to exhaustion. Scientists worldwide have already said actively and passively that we are facing one of the biggest problems ever: climate change. This is unsustainable and we must try to revert it, or, if we are too late, slow it down as much as possible. To make this happen, there are many possible methods. In this review, we investigate catalysts for using water as an energy source, or, instead of water, alcohols. On the other hand, the recycling of gases such as CO2 and N2O is also addressed, but we also observe non-catalytic means of generating energy through solar cell production.

Selective Solar Harvesting Windows for Full-Spectrum Utilization

Smart windows can selectively regulate excess solar radiation to reduce heating and cooling energy consumption in the built environment. However, the inevitable dissipation of ultraviolet and near-infrared into waste heat results in inefficient solar utilization. Herein, a dual-band selective solar harvesting (SSH) window is developed to realize full-spectrum utilization. A transparent photovoltaic, converting ultraviolet into electricity, and a transparent solar absorber, converting near-infrared into thermal energy, are integrated and coupled with a ventilation system to extract heat for indoor use. Compared with common transparent photovoltaics, the SSH window increases solar harvesting efficiency up to threefold while maintaining a considerable visible transmittance. Simulations suggest that the SSH window, besides generating electricity, delivers energy savings by over 30% higher than common smart windows. This is the first integration of transparent photovoltaic and transparent solar absorber into a window, which may open up a new avenue for the development of energy-efficient buildings.

Theory-Guided Material Design Enabling High-Performance Multifunctional Semitransparent Organic Photovoltaics without Optical Modulations

Semitransparent organic photovoltaics (ST-OPVs) have drawn great attention for promising applications in building-integrated photovoltaics, providing additional power generation for daily use. A previously proposed strategy, "complementary NIR absorption," is widely applied for high-performance ST-OPVs. However, rational material design toward high performance has not been achieved. In this work, an external quantum efficiency (EQE) model describing this strategy is developed to explore the full potential of material design on ST-OPV performance. Guided by the model, a novel nonfullerene acceptor (NFA), ATT-9, is designed and synthesized, which possesses optimal bandgap for ST-OPVs, achieving a record short-circuit current density of 30 mA cm^-2 and a power conversion efficiency of 13.40%, the highest value among devices based on NFAs with bandgaps lower than 1.2 eV. It is notworthy that, at such a low bandgap, the energy loss of the device is only 0.58 eV, which is attributed to the low energetic disorder confirmed by an ultralow Urbach energy of 21.6 meV. Benefiting from the optimal bandgap and low energy loss, the ATT-9-based ST-OPV achieves a high light utilization efficiency of 3.33% without optical modulations, and meanwhile shows excellent thermal insulation, exceeding the commercial 3M heat-insulating window film, demonstrating the outstanding application prospects of multifunctional ST-OPVs.

Recent Progress in Developing Monolithic Perovskite/Si Tandem Solar Cells

Monolithic perovskite/Silicon tandem solar cells have reached a certified efficiency of 29. 1% in recent years. In this review, we discuss material design for monolithic perovskite/Si tandem solar cells, with the focus on the top-cell development to improve their performance. Firstly, we introduce different types of transparent electrodes with high transmittance and low sheet-resistance used in tandem solar cells. We then discuss the development of the wide-bandgap perovskite absorber for top-cells, especially the strategies to obtain the perovskite layers with good efficiency and stability. In addition, as a special functional layer in tandem solar cells, the recombination layers play an important role in device performance, wherein different configurations are summarized. Furthermore, tandem device cost analysis is discussed. This review summarizes the progress of monolithic perovskite/Silicon tandem solar cells in a pragmatic perspective, which may promote the commercialization of this technology.

Toward Visibly Transparent Organic Photovoltaic Cells Based on a Near-Infrared Harvesting Bulk Heterojunction Blend

Wavelength-selective harvesting by organic solar cells (OSCs) has attracted significant research attention due to the unique potential of these materials for smart photovoltaic window applications. Here, a visibly transparent OSC is demonstrated by utilizing both near-infrared (NIR)-absorbing polymer donor and nonfullerene acceptor (NFA) materials with narrow optical band gaps of less than 1.4 eV. Despite the substantial overlap in absorption spectra between the donor and acceptor, sufficient lowest unoccupied molecular orbital (LUMO) and highest occupied molecule orbital (HOMO) energy offsets for efficient charge separation with concurrent very low voltage losses yield a power conversion efficiency (PCE) of 9.13%. Moreover, with the introduction of an ultrathin Ag film (8 nm) as a transparent top electrode, semitransparent OSCs exhibit an excellent dual-side photovoltaic performance of 5.7 and 3.9% under bottom and top illumination, respectively, with high transmittance reaching 60% at wavelengths from 400 to 600 nm. This approach is expected to provide a new perspective in developing the highly efficient and transparent OSCs.

Efficient Low-Cost All-Flexible Microcavity Semitransparent Polymer Solar Cells Enabled by Polymer Flexible One-Dimensional Photonic Crystals

High-efficiency low-cost all-flexible microcavity semitransparent polymer solar cells (STPSCs) are comparatively studied in both fullerene- and nonfullerene-based systems with the structure strategy, employing polymer flexible one-dimensional photonic crystals (F-1DPCs), as well as indium tin oxide-free UV/ozone plasma-treated polymer/ultrathin metal and PEDOT:PSS transparent electrodes. Based on the reasonable optimization of electrical and optical characteristics in the device, the maximum power conversion efficiency with the use of polymer F-1DPCs can be greatly improved by 24-27% compared to the respective control devices. The improvement in J_SC is comprehensively discussed, which is mainly ascribed to the enhancement of effective photon absorption in the device. Although color tunability of fullerene and nonfullerene all-flexible STPSCs can be easily achieved with the use of different photonic band gaps of polymer F-1DPCs, the CIE coordinates of nonfullerene STPSCs differ a lot from the original light source compared to the fullerene ones because of a high absorption coefficient in a narrow wavelength region. This work presents an easy and effective microcavity device strategy incorporated with different elements and demonstrates a new sketch of structure-absorption-performance relationships for fullerene- versus nonfullerene-based all-flexible STPSCs, which is compatible with low-cost roll-to-roll manufacturing and surely has a diversity of potential applications to better meet specific needs.

Retarding Ion Exchange between Conducting Polymers and Ionic Liquids for Printable Top Electrodes in Semitransparent Organic Solar Cells

Semitransparent organic solar cells (ST-OSCs) are considered to be an influential tool for aesthetic and economic building-integrated photovoltaics, which can be fabricated by the printing technology. A poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) and ionic liquid (IL) composite has been considered as an electrode for ST-OSCs because of its high electrical conductivity, high transparency, and printability. However, we found that the introduction of IL into the PEDOT:PSS solution for enhancing its electrical conductivity results in (1) nonreliable printing of PEDOT:PSS/IL composite films because of gradual gelation of the mixture solution and (2) the production of chemically reactive ion pairs during ion exchange between PSS and IL, which induces the oxidation of the underlying organic semiconductors during printing. To solve these problems, we developed a sequential printing method using pristine PEDOT:PSS and IL solutions to retard ion exchange, thus preventing chemical doping of organic semiconductors by newly generated ion pairs. Finally, by using only solution processes, we demonstrate efficient ST-OSCs with a printed PEDOT:PSS/IL composite as the top electrode, exhibiting a power conversion efficiency of 6.32% at an average visible transmittance of 35.4%.

Stretchable/flexible silver nanowire Electrodes for energy device applications

Research on sustainable and high-efficiency energy devices has recently emerged as an important global issue. These devices are now moving beyond the form of a bulk, rigid platform to a portable, flexible/stretchable format that is easily available in our daily lives. Similar to the development of an active layer for the production of next-generation energy devices, the fabrication of flexible/stretchable electrodes for the easy flow of electrons is also very important. Silver nanowire electrodes have high electronic conductivity even in a flexible/stretchable state due to their high aspect ratio and percolation network structures compared to conventional electrodes. Herein, we summarize the research in the field of flexible/stretchable electronics on energy devices fabricated using silver nanowires as the electrodes. Additionally, for a systematic presentation of the current research trends, this review classifies the surveyed research efforts into the categories of energy production, storage, and consumption.

Solution-Processed Semitransparent Organic Photovoltaics: From Molecular Design to Device Performance

Recent research efforts on solution-processed semitransparent organic solar cells (OSCs) are presented. Essential properties of organic donor:acceptor bulk heterojunction blends and electrode materials, required for the combination of simultaneous high power conversion efficiency (PCE) and average visible transmittance of photovoltaic devices, are presented from the materials science and device engineering points of view. Aspects of optical perception, charge generation-recombination, and extraction processes relevant for semitransparent OSCs are also discussed in detail. Furthermore, the theoretical limits of PCE for fully transparent OSCs, compared to the performance of the best reported semitransparent OSCs, and options for further optimization are discussed.

Graphene- and Carbon-Nanotube-Based Transparent Electrodes for Semitransparent Solar Cells

A substantial amount of attention has been paid to the development of transparent electrodes based on graphene and carbon nanotubes (CNTs), owing to their exceptional characteristics, such as mechanical and chemical stability, high carrier mobility, high optical transmittance, and high conductivity. This review highlights the latest works on semitransparent solar cells (SSCs) that exploit graphene- and CNT-based electrodes. Their prominent optoelectronic properties and various fabrication methods, which rely on laminated graphene/CNT, doped graphene/CNT, a hybrid graphene/metal grid, and a solution-processed graphene mesh, with applications in SSCs are described in detail. The current difficulties and prospects for future research are also discussed.

High-Efficiency and High-Color-Rendering-Index Semitransparent Polymer Solar Cells Induced by Photonic Crystals and Surface Plasmon Resonance

Semitransparent polymer solar cells (ST-PSCs) show attractive potential in power-generating windows or building-integrated photovoltaics. However, the development of ST-PSCs is lagging behind opaque PSCs because of the contradiction between device efficiency and transmission. Herein, Ag/Au alloy nanoparticles and photonic crystals (PCs) were simultaneously introduced into ST-PSCs, acting compatibly as localized surface plasmon resonances and distributed Bragg reflectors to enhance light absorption and transmission. As a result, ST-PSCs based on a hybrid PTB7-Th:PC₇₁BM active layer contribute an efficiency as high as 7.13 ± 0.15% and an average visible transmission beyond 20%, which are superior to most of the reported results. Furthermore, PCs can partly compensate valley range of transmission by balancing reflection and transmission regions, yielding a high color rendering index of 95. We believe that the idea of two light management methods compatibly enhancing the performance of ST-PSCs can offer a promising path to develop photovoltaic applications.

Efficient Semitransparent Organic Solar Cells with Tunable Color enabled by an Ultralow-Bandgap Nonfullerene Acceptor

Semitransparent organic solar cells (OSCs) show attractive potential in power-generating windows. However, the development of semitransparent OSCs is lagging behind opaque OSCs. Here, an ultralow-bandgap nonfullerene acceptor, "IEICO-4Cl", is designed and synthesized, whose absorption spectrum is mainly located in the near-infrared region. When IEICO-4Cl is blended with different polymer donors (J52, PBDB-T, and PTB7-Th), the colors of the blend films can be tuned from purple to blue to cyan, respectively. Traditional OSCs with a nontransparent Al electrode fabricated by J52:IEICO-4Cl, PBDB-T:IEICO-4Cl, and PTB7-Th:IEICO-4Cl yield power conversion efficiencies (PCE) of 9.65 ± 0.33%, 9.43 ± 0.13%, and 10.0 ± 0.2%, respectively. By using 15 nm Au as the electrode, semitransparent OSCs based on these three blends also show PCEs of 6.37%, 6.24%, and 6.97% with high average visible transmittance (AVT) of 35.1%, 35.7%, and 33.5%, respectively. Furthermore, via changing the thickness of Au in the OSCs, the relationship between the transmittance and efficiency is studied in detail, and an impressive PCE of 8.38% with an AVT of 25.7% is obtained, which is an outstanding value in the semitransparent OSCs.

Emerging Semitransparent Solar Cells: Materials and Device Design

Semitransparent solar cells can provide not only efficient power-generation but also appealing images and show promising applications in building integrated photovoltaics, wearable electronics, photovoltaic vehicles and so forth in the future. Such devices have been successfully realized by incorporating transparent electrodes in new generation low-cost solar cells, including organic solar cells (OSCs), dye-sensitized solar cells (DSCs) and organometal halide perovskite solar cells (PSCs). In this review, the advances in the preparation of semitransparent OSCs, DSCs, and PSCs are summarized, focusing on the top transparent electrode materials and device designs, which are all crucial to the performance of these devices. Techniques for optimizing the efficiency, color and transparency of the devices are addressed in detail. Finally, a summary of the research field and an outlook into the future development in this area are provided.

Efficient Semitransparent Solar Cells with High NIR Responsiveness Enabled by a Small-Bandgap Electron Acceptor

Inspired by the remarkable promotion of power conversion efficiency (PCE), commercial applications of organic photovoltaics (OPVs) can be foreseen in near future. One of the most promising applications is semitransparent (ST) solar cells that can be utilized in value-added applications such as energy-harvesting windows. However, the single-junction STOPVs utilizing fullerene acceptors show relatively low PCEs of 4%-6% due to the limited sunlight absorption because it is a dilemma that more photons need to be harvested in UV-vis-near-infrared (NIR) region to generate high photocurrent, which leads to the significant reduction of device transparency. This study describes the development of a new small-bandgap electron-acceptor material ATT-2, which shows a strong NIR absorption between 600 and 940 nm with an E_g^opt of 1.32 eV. By combining with PTB7-Th, the as-cast OPVs yield PCEs of up to 9.58% with a fill factor of 0.63, an open-circuit voltage of 0.73 V, and a very high short-circuit current of 20.75 mA cm^-2 . Owing to the favorable complementary absorption of low-bangap PTB7-Th and small-bandgap ATT-2 in NIR region, the proof-of-concept STOPVs show the highest PCE of 7.7% so far reported for single-junction STOPVs with a high transparency of 37%.

Fast-Response Photonic Device Based on Organic-Crystal Heterojunctions Assembled into a Vertical-Yet-Open Asymmetric Architecture

Crystalline dioctyl-3,4,9,10-perylenedicarboximide nanowires and 6,13-bis(triisopropylsilylethynyl) pentacene microplates are integrated into a vertical-yet-open asymmetrical heterojunction for the realization of a high-performance organic photovoltaic detector, which shows fast photoresponse, ultrahigh signal-to-noise ratio, and high sensitivity to weak light.

Coloring Semitransparent Perovskite Solar Cells via Dielectric Mirrors

While perovskite-based semitransparent solar cells for window applications show competitive levels of transparency and efficiency compared to organic photovoltaics, the color perception of the perovskite films is highly restricted because band gap engineering results in losses in power conversion efficiencies. To overcome the limitation in visual aesthetics, we combined semitransparent perovskite solar cells with dielectric mirrors. This approach enables one to tailor the device appearance to almost any desired color and simultaneously offers additional light harvesting for the solar cell. In the present work, opto-electrical effects are investigated through quantum efficiency and UV-to-visible spectroscopic measurements. Likewise, a detailed chromaticity analysis, featuring the transmissive and reflective color perception of the device including the mirror, from both sides and in different illumination conditions, is presented and analyzed. Photocurrent density enhancement of up to 21% along with overall device transparency values of up to 31% (4.2% efficiency) is demonstrated for cells showing a colored aesthetic appeal. Finally, a series of simulations emulating the device chromaticity, transparency, and increased photocurrent density as a function of the photoactive layer thickness and the design wavelength of the dielectric mirror are presented. Our simulations and their experimental validation enabled us to establish the design rules that consider the color efficiency/transparency interplay for real applications.

Thermal and Environmental Stability of Semi-Transparent Perovskite Solar Cells for Tandems Enabled by a Solution-Processed Nanoparticle Buffer Layer and Sputtered ITO Electrode

A sputtered oxide layer enabled by a solution-processed oxide nanoparticle buffer layer to protect underlying layers is used to make semi-transparent perovskite solar cells. Single-junction semi-transparent cells are 12.3% efficient, and mechanically stacked tandems on silicon solar cells are 18.0% efficient. The semi-transparent perovskite solar cell has a T 80 lifetime of 124 h when operated at the maximum power point at 100 °C without additional sealing in ambient atmosphere under visible illumination.

A Large-Bandgap Conjugated Polymer for Versatile Photovoltaic Applications with High Performance

A new copolymer PM6 based on fluorothienyl-substituted benzodithiophene is synthesized and characterized. The inverted polymer solar cells based on PM6 exhibit excellent performance with Voc of 0.98 V and power conversion efficiency (PCE) of 9.2% for a thin-film thickness of 75 nm. Furthermore, the single-junction semitransparent device shows a high PCE of 5.7%.

A Methoxydiphenylamine-Substituted Carbazole Twin Derivative: An Efficient Hole-Transporting Material for Perovskite Solar Cells

The small-molecule-based hole-transporting material methoxydiphenylamine-substituted carbazole was synthesized and incorporated into a CH3NH3PbI3 perovskite solar cell, which displayed a power conversion efficiency of 16.91%, the second highest conversion efficiency after that of Spiro-OMeTAD. The investigated hole-transporting material was synthesized in two steps from commercially available and relatively inexpensive starting reagents. Various electro-optical measurements (UV/Vis, IV, thin-film conductivity, hole mobility, DSC, TGA, ionization potential) have been carried out to characterize the new hole-transporting material.

A generic concept to overcome bandgap limitations for designing highly efficient multi-junction photovoltaic cells

The multi-junction concept is the most relevant approach to overcome the Shockley–Queisser limit for single-junction photovoltaic cells. The record efficiencies of several types of solar technologies are held by series-connected tandem configurations. However, the stringent current-matching criterion presents primarily a material challenge and permanently requires developing and processing novel semiconductors with desired bandgaps and thicknesses. Here we report a generic concept to alleviate this limitation. By integrating series- and parallel-interconnections into a triple-junction configuration, we find significantly relaxed material selection and current-matching constraints. To illustrate the versatile applicability of the proposed triple-junction concept, organic and organic-inorganic hybrid triple-junction solar cells are constructed by printing methods. High fill factors up to 68% without resistive losses are achieved for both organic and hybrid triple-junction devices. Series/parallel triple-junction cells with organic, as well as perovskite-based subcells may become a key technology to further advance the efficiency roadmap of the existing photovoltaic technologies.

The efficiency of a single-junction photovoltaic cell is constrained by the Shockley-Queisser limit. Here, the authors adopt a triple-junction configuration which relaxes material and current-matching constraints, providing a generic strategy for advancing the efficiency roadmap of photovoltaic technologies.

Highly efficient semitransparent polymer solar cells with color rendering index approaching 100 using one-dimensional photonic crystal

Window application is the important aim for semitransparent solar cells (STPSC) investigation. Here, we demonstrate a method to achieve significantly improved color rendering index (CRI), depressed chromaticity difference (DC), and enhanced power conversion efficiency (PCE) simultaneously by introducing the one-dimensional photonic crystals (1DPCs) Bragg reflector structure onto the STPSC. The device performance is studied from aspects of color perception, electrical properties, and theoretical optical simulations. The STPSCs exhibit achromatic transparency nature color perceptions, especially for the STPSCs with 1DPCs (pairs ≥ 3) under AM 1.5G illumination light source, standard illuminant D65, and standard illuminant A. The excellent CRI is approaching 97 with lower DC about 0.0013 for the device with 5 pairs of 1DPC illumined by AM 1.5G illumination light source. At the same time, the PCE of STPSC devices with 5 pairs of 1DPC was improved from 4.87 ± 0.14% to 5.31 ± 0.13% compared to without. This method provides a facilitative approach to realizing excellent SPTSC window application.

Linked-Acceptor Type Conjugated Polymer for High Performance Organic Photovoltaics with an Open-Circuit Voltage Exceeding 1 V

A linked-acceptor type conjugated polymer is designed and sythesized based on 4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene (BDTT) and linked-thieno[3,4-c]pyrrole-4,6-dione (LTPD). This polymer uses alkyl-substituted thiophene as a bridge. The PBDTT-LTPD includes two TPD units in one repeating unit, which can enhance acceptor density in the polymer backbone and lower the highest occupied molecular orbital (HOMO) level. By contrast, variable alkyl substitutions in the thiophene-bridges ensure the subtle regulation of polymer properties. The solar cells based on PBDTT-LTPD display an open-circuit voltage (Voc) that exceeds 1 V, and a maximum power conversion efficiency (PCE) of 7.59% is obtained. This PCE value is the highest for conventional single-junction bulk heterojunction solar cells with Voc values of up to 1 V. Given that PBDTT-LTPD exhibits a low HOMO energy level and a band gap equivalent to that of poly(3-hexylthiophene), PBDTT-LTPD/phenyl-C61-butyric acid methyl ester may be a promising candidate for the front cell in tandem polymer solar cells.

Semitransparent polymer solar cells with simultaneously improved efficiency and color rendering index

We demonstrate a high performance STPSC with a significantly improved CRI of 91 and a PCE of 5.01% by introducing 1DPCs.

Organic-inorganic halide perovskite/crystalline silicon four-terminal tandem solar cells

Tandem solar cells constructed from a crystalline silicon (c-Si) bottom cell and a low-cost top cell offer a promising way to ensure long-term price reductions of photovoltaic modules. We present a four-terminal tandem solar cell consisting of a methyl ammonium lead triiodide (CH3NH3PbI3) top cell and a c-Si heterojunction bottom cell. The CH3NH3PbI3 top cell exhibits broad-band transparency owing to its design free of metallic components and yields a transmittance of >55% in the near-infrared spectral region. This allows the generation of a short-circuit current density of 13.7 mA cm(-2) in the bottom cell. The four-terminal tandem solar cell yields an efficiency of 13.4% (top cell: 6.2%, bottom cell: 7.2%), which is a gain of 1.8%abs with respect to the reference single-junction CH3NH3PbI3 solar cell with metal back contact. We employ the four-terminal tandem solar cell for a detailed investigation of the optical losses and to derive guidelines for further efficiency improvements. Based on a power loss analysis, we estimate that tandem efficiencies of ∼28% are attainable using an optically optimized system based on current technology, whereas a fully optimized, ultimate device with matched current could yield up to 31.6%.

Fully solution-processing route toward highly transparent polymer solar cells

We report highly transparent polymer solar cells using metallic silver nanowires (AgNWs) as both the electron- and hole-collecting electrodes. The entire stack of the devices is processed from solution using a doctor blading technique. A thin layer of zinc oxide nanoparticles is introduced between photoactive layer and top AgNW electrode which plays decisive roles in device functionality: it serves as a mechanical foundation which allows the solution-deposition of top AgNWs, and more importantly it facilitates charge carriers extraction due to the better energy level alignment and the formation of ohmic contacts between the active layer/ZnO and ZnO/AgNWs. The resulting semitransparent polymer:fullerene solar cells showed a power conversion efficiency of 2.9%, which is 72% of the efficiency of an opaque reference device. Moreover, an average transmittance of 41% in the wavelength range of 400-800 nm is achieved, which is of particular interest for applications in transparent architectures.

A cracked polymer templated metal network as a transparent conducting electrode for ITO-free organic solar cells

We report a highly transparent, low resistance Ag metal network templated by a cracked polymer thin film and its incorporation in an organic solar cell. The performance of this scalable metallic network is comparable to that of conventional ITO electrodes. This is a general approach to replace ITO in diverse thin film devices.