Mechanism for Flexible Solar Cells

Flexible solar cells have a lot of market potential for application in photovoltaics integrated into buildings and wearable electronics because they are lightweight, shockproof and self-powered. Silicon solar cells have been successfully used in large power plants. However, despite the efforts made for more than 50 years, there has been no notable progress in the development of flexible silicon solar cells because of their rigidity1–4. Here we provide a strategy for fabricating large-scale, foldable silicon wafers and manufacturing flexible solar cells. A textured crystalline silicon wafer always starts to crack at the sharp channels between surface pyramids in the marginal region of the wafer. This fact enabled us to improve the flexibility of silicon wafers by blunting the pyramidal structure in the marginal regions. This edge-blunting technique enables commercial production of large-scale (>240 cm2), high-efficiency (>24%) silicon solar cells that can be rolled similarly to a sheet of paper. The cells retain 100% of their power conversion efficiency after 1,000 side-to-side bending cycles. After being assembled into large (>10,000 cm2) flexible modules, these cells retain 99.62% of their power after thermal cycling between −70 °C and 85 °C for 120 h. Furthermore, they retain 96.03% of their power after 20 min of exposure to air flow when attached to a soft gasbag, which models wind blowing during a violent storm.

Flexible solar cells have launched potential applications in diverse areas, such as civil engineering, consumer electronics, electric automobile, and aerospace use. In recent years, perovskite solar cells (PSCs) have been successful with a rocketing power conversion efficiency (PCE) from 3.8% to 25.2% in the last decade. Due to its material flexibility, together with low‐cost and facile fabrication processes, perovskites have certainly been considered as a promising candidate for the next generation of flexible solar cells. So far, the PCE of single‐junction flexible perovskite solar cells (FPSCs) has reached 19.51%, which retains researchers' great enthusiasm for further development and applications of FPSCs. Herein, a brief review of the recent advances in the structural components of FPSCs is presented, including perovskite absorber layers, flexible substrates, transparent bottom electrodes, and charge carrier transport layers. In particular, the focus is on the development of low‐temperature fabrication processes of the aforementioned compositional layer structures. Finally, noticeable achievements and annual milestones are discussed and summarized, and suggestions for further improvement of FPSCs and their ways toward commercialization are presented.

The development of flexible solar cells is necessary for achieving market competitiveness through the implementation of low cost solar cells and for applying customized business models, such as Building Integrated Photovoltaics (BIPV). Cu2ZnSn(S,Se)S4 (CZTSSe) thin films have attracted attention as low-cost absorber materials for solar cells; however, further studies are required to develop flexible solar cells from this material and to achieve a high power conversion efficiency. In this work, the carrier separation characteristics of flexible CZTSSe thin-film solar cells on Mo foil substrates were identified. The surface electrical characteristics of the CZTSSe absorber layer indicate that the topography, surface potential, and local current are proportional to one another, in contrast to the characteristics exhibited by CIGS cells. For the CZTSSe absorber layer, an upward band bending-like band structure formed at and near the GBs, and a current path formed along the IGs as holes collected toward the GBs, and electrons collected toward the IGs. In contrast to that in CIGS cells, the carrier separation induced by the formation of the upward band bending-like band structure at the GBs is crucial in CZTSSe thin-film solar cells. Furthermore, the positive potential distribution at the IGs and average potential difference showed a proportional relationship to the local current and PCE. Through the implementation of these carrier separation characteristics, a flexible CZTSSe thin-film solar cell on a Mo foil substrate achieved a PCE of over 7%. Acknowledge: This work was supported by the Korea Institute of Energy Technology Evaluation and Planning (KETEP) and the Ministry of Trade, Industry & Energy (MOTIE) (No. 20173010012980) and by the DGIST R&D Programs of the Ministry of Science, ICT & Future Planning of Korea (19-BD-05).

Organic-inorganic hybrid perovskite solar cells have experienced a skyrocketing photoelectric conversion efficiency (PCE) increase in recent years, and become the “rock star” in the field of solar cells. After only 4 years, the certificated PCE of these materials based solid state solar cells have reach the maximum 22.1%, which is comparable to the highest PCE of the commercial silicon-based solar cells and higher than those of the organic solar cells and the dye-sensitized solar cells. Besides the promising efficiency, these materials surpass its competitors with the adaptability to solution- process at low-temperature and in air, and better flexibility, which can lead to lower large-scale production cost and more application potential for wearable electronics. The outstanding device performance of the hybrid perovskite solar cells have attracted intensive research interest, and besides increasing the PCE, lots of efforts have been focused on functional diversification for this solar cells. Compare to the commercial solar cells based on rigid silicon, organic- inorganic hybrid perovskite materials exhibit better flexibility which is beneficial for applications in flexible electronic devices, and due to the mild preparation conditions and the solution processablity, it is easy to prepare a variety of nanostructures. Those advantages have expanded the application scope of the hybrid perovskite materials, especially for fabricating flexible and semi-transparent solar cells which have potential use in building integrated photovoltaic such as solar cell windows and solar cell curtains. Here in this review, we focus on the recent progress of the flexible and semi-transparent solar cells based on organic-inorganic hybrid perovskite materials. In the part of the flexible hybrid perovskite solar cells, two mainstream device structures, namely planar and fiber-shaped devices, are discussed and the device structure and materials selection are analyzed in detail. As for the planar flexible perovskite solar cells, the choosing of the low-temperature processable function materials for the solar cells seems to be one of key factors due to the fact that most flexible planar substrates are vulnerable to the high-temperature treatments. As for the fiber-shaped perovskite solar cells, the choosing of the proper transparent conductive electrode materials is crucial which should have a good balance between the transparency and conductivity, and due to the difficulty of forming high-quality perovskite function layer on the curved surface of a certain wire, the prepare methods have to be upgraded too. In the part of the semi-transparent hybrid perovskite solar cells, two main strategies (reducing film thickness and forming isolated island structure) are discussed and a lot of reported preparation methods are analyzed in detail. As for the former strategy of reducing film thickness, the advantages are the comparatively higher PCE, easier manufacture and better controllability and the disadvantage is the unfavorable brownish color. As for the latter strategy of forming isolated island structure, the advantage is the better full-spectrum transmission and the disadvantages are comparatively more complicated manufacture and worse controllability. The whole paper has presented the development of the flexible and semi-transparent perovskite solar cells so far and gave detailed discussions for the reported works. Based on these analyzations, the organic-inorganic hybrid perovskites will find their special and unique position in the field of flexible and semi-transparent solar cells and may aggressively push the field forward.

Flexible thin film solar cells have attracted a great deal of attention as mobile power sources and key components for building-integrated photovoltaics, due to their light weight and flexible features in addition to compatibility with low-cost roll-to-roll fabrication processes. Among many thin film materials, organometallic perovskite materials are emerging as highly promising candidates for high efficiency thin film photovoltaics; however, the performance, scalability, and reliability of the flexible perovskite solar cells still have large room to improve. Herein, we report highly efficient, flexible perovskite solar cells fabricated on ultrathin flexible glasses. In such a device structure, the flexible glass substrate is highly transparent and robust, with low thermal expansion coefficient, and perovskite thin film was deposited with a thermal evaporation method that showed large-scale uniformity. In addition, a nanocone array antireflection film was attached to the front side of the glass substrate in order to improve the optical transmittance and to achieve a water-repelling effect at the same time. It was found that the fabricated solar cells have reasonable bendability, with 96% of the initial value remaining after 200 bending cycles, and the power conversion efficiency was improved from 12.06 to 13.14% by using the antireflection film, which also demonstrated excellent superhydrophobicity.

Top PV market solar cells 2016

We investigated the characteristics of nano crystalline silicon(nc-Si) thin-film solar cells on graphite substrates. Amorphous silicon(a-Si) thin-film solar cells on graphite plates show low conversion efficiency due to high surface roughness, and many recombination by dangling bonds. In previous studies, we deposited barrier films by plasma enhanced chemical vapor deposition(PECVD) on graphite plate to reduce surface roughness and achieved ~7.8 % cell efficiency. In this study, we fabricated nc-Si thin film solar cell on graphite in order to increase the efficiency of solar cells. We achieved 8.45 % efficiency on graphite plate and applied this to nc-Si on graphite sheet for flexible solar cell applications. The characterization of the cell is performed with external quantum efficiency(EQE) and current density-voltage measurements(J-V). As a result, we obtain ~8.42 % cell efficiency in a flexible solar cell fabricated on a graphite sheet, which performance is similar to that of cells fabricated on graphite plates.

1 - Introduction

For the development of high efficiency Cu(In,Ga)Se 2 (CIGS) flexible solar cells on polymer films with efficient and robust deposition process the so-called three-stage evaporation processes were modified. CIGS layers were grown by co-evaporation of constituent elements at low substrate temperature compatible with the stability of the polyimide film. The CIGS layers grown with our standard process are compositionally graded, especially the Ga has a strong grading profile across the layer thickness. Different variations of the standard evaporation process were investigated, especially in view of changing the energy band gap profiles in the absorber layer for achieving further improvements in high efficiency solar cells. Further on, the incorporation of sodium during the CIGS deposition was optimized. Structural and chemical composition properties of CIGS layers were characterized with SEM, XRF, SIMS and the photovoltaic properties were characterized with I–V and quantum efficiency measurements. A flexible CIGS solar cell on polyimide film with a record efficiency of 17.6% has been developed.

Halide perovskite films processed from solution at low-temperature offer promising opportunities to make flexible solar cells. However, the brittleness of perovskite films is an issue for mechanical stability in flexible devices. Herein, photo-crosslinked [6,6]-phenylC61 -butyric oxetane dendron ester (C-PCBOD) is used to improve the mechanical stability of methylammonium lead iodide (MAPbI3 ) perovskite films. Also, it is demonstrated that C-PCBOD passivates the grain boundaries, which reduces the formation of trap states and enhances the environmental stability of MAPbI3 . Thus, MAPbI3 perovskite solar cells are prepared on solid and flexible substrates with record efficiencies of 20.4% and 18.1%, respectively, which are among the highest ever reported for MAPbI3 on both flexible and solid substrates. The result of this work provides a step improvement toward stable and efficient flexible perovskite solar cells.

Smaller texture improves flexibility of crystalline silicon solar cells

Enhanced mechanical endurance and power conversion efficiency in flexible Cu2ZnSnS4 solar cells using ZnO/Ag-Ag2O/ZnO film

Flexible solar cells have been considered as a promising photovoltaic (PV) technology due to their intrinsic advantages such as lightweight and bendability, which make them very convenient for transportation, installation, and integration with architectures and wearable electricity‐generating devices. As a novel PV technology being compatible with roll‐to‐roll fabrication, flexible perovskite solar cells (FPSCs) have achieved a great progress within the past few years, partially due to the superior photoelectronic properties of the halide perovskite absorber and the easy fabrication of the device. As a result, the champion power conversion efficiency of the FPSCs has exceeded 18% recently. In this review, the recent developments of FPSCs are summarized and discussed in the following four aspects: perovskite absorbers, flexible substrates, transparent conductive electrodes, and carrier transport layers, which are the main components for a FPSC device. The flexibility, stability, and other properties are also discussed in terms of the specialized FPSC devices. Finally, a rough prediction for the future development of FPSCs is provided at the end of this review.

With the continuous development of various new energy sources, flexible solar cells have attracted much attention as a renewable and clean energy source. Compared with rigid solar cells, flexible solar cells have the characteristics of bendability, flexibility, and portability. Choosing the right material and manufacturing process can get twice the result with half the effort in the research of flexible solar cells. This article aims to review the research progress of wearable flexible solar cells, analyze the materials and preparation technologies used in flexible solar cells at this stage, and discuss the influence of some materials and processes on the photoelectric conversion efficiency and flexibility of flexible solar cells. In addition, this paper also discusses the future development prospects and some existing problems of flexible solar cells. With the continuous development of wearable technology, the research of flexible solar cells must be one of the development priorities in the future.

Diversifying Progress in Solar