Development Of Flexible Solar Cells Research Articles

Current status and prospects of flexible solar cells

With the increasing global demand for clean energy, solar cells, as a renewable and pollution-free clean energy source, have attracted much attention. In the past, solar cells have always used rigid materials as substrates. However, this rigid solar panel is not only bulky and limited in layout, but also susceptible to external impact and damage, which is not conducive to its application in various scenarios. Flexible solar cells, developed from rigid solar cells, have the advantages of light weight, small size, high safety, and strong adaptability, gradually becoming the development trend of solar cells. The research and development of flexible solar cells benefit from the rapid development of materials. In recent years, the emergence of various new materials and preparation technologies, such as carbon fibers, polymers, organic materials, and nanostructures, has provided a better foundation for the preparation of flexible batteries. At the same time, flexible batteries can also be processed through printing, spraying and other processing methods, improving manufacturing efficiency. In addition, the demand for wearable devices, smart homes and other emerging scenarios in society has also accelerated the research and application of flexible solar cells, providing broad application prospects for their development. However, its cost is usually higher than that of rigid solar cells, and market regulation under new categories requires time to adapt. The development of flexible solar cells is benign, but it requires the market to test its standardization.

Flexible Crystalline-Silicon Photovoltaics: Light Management with Surface Structures

ConspectusFlexible solar cells have been intensively studied in recent years for their applicability on curved or uneven surfaces, which augments their versatility toward various applications. Although emerging materials such as organics/polymers, perovskite, amorphous silicon, and copper indium gallium selenide have been used as light absorption materials for flexible solar cells, the commercialization of these materials is limited owing to their efficiency degradation, usage of toxic materials, short lifespan, or scarcity. On the contrary, crystalline silicon (c-Si) solar cells have been commercialized because of their low manufacturing cost, long lifespan of over 20 years, and high power-conversion efficiency (PCE) of ≤26.7%. However, the development of flexible solar cells using c-Si substrate poses an intrinsic problem resulting from its rigid material characteristics. In recent years, flexible solar cells using thin c-Si wafers have become more attractive with archiving a higher PCE than that of the emerging flexible solar cells. In addition, the mechanical flexibility can be realized using a thin c-Si film with a thickness of ≤50 μm, which is a quarter of the substrate thickness of conventional c-Si solar cells. Nonetheless, thin c-Si-based flexible solar cells face critical challenges because of severe light absorption loss in the entire wavelength region (300–1100 nm) because of the low absorption coefficient and surface reflection of c-Si. The development of the c-Si flexible solar cells should focus on improving the light absorption of thin c-Si films as well as maintaining the mechanical flexibility and stability of the thin c-Si solar cells. Thus, in this Account, we introduce high-aspect-ratio c-Si microwires and a random inverted-pyramidal-transparent optical film as promising surface structures for the efficient trapping of incident light in thin c-Si films. Moreover, the principles regarding the improvement in light absorption of these surface structures are discussed along with the implementable strategies for maximizing PCE of the c-Si flexible solar cells. Lastly, perspectives on further improvement of the PCE and stability of the flexible c-Si solar cells are presented.

Flexible Cu2znsn(S, Se)4 Solar Cells over 7% Power Conversion Efficiency

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).

Effects of Sn Incorporation in ZnO Thin Films on Properties of Perovskite Solar Cells

Properties of electron transporting layer (ETL) play an important role on photovoltaic performances of perovskite solar cells. In this work, effects of Sn incorporation on properties of ZnO-based perovskite solar cells were investigated. Sn-doped ZnO (TZO) thin film as ETL was prepared via a sol–gel method. With 5% atom doping, TZO film coated on an indium doped tin oxide (ITO) substrate provided comparable light transmittance with that of an undoped ZnO/ITO substrate. It was also found that the optical band gap of TZO film (3.30 eV) is slightly wider than that of the ZnO one (3.28 eV). These results suggest that Sn atoms probably incorporated into the ZnO crystal during the sol-gel method. The grains size of perovskite layer coated on TZO or ZnO films also showed variation. The perovskite crystal on the TZO thin film (average 300 nm) was larger than that of the one on ZnO thin film (average 277 nm). The preliminary results indicate that the perovskite solar cell based on TZO film provided higher power conversion efficiency (PCE) of 4.42 % than the ZnO-based device (3.16%). Short-circuit current density (Jsc), open-circuit voltage (Voc) and fill factor (FF) of TZO-based device were also higher than the ZnO-based device. This may be because TZO film may provide lower resistivity and better ETL/perovskite interface contact, confirmed by lower series resistance and higher shunt resistance of the TZO-based device. Finally, this work introduced a simple method to prepare TZO film at low temperature for photovoltaic application. It may help guide the development of flexible solar cells and other optoelectronic devices.

High flexible Cu2ZnSn(S,Se)4 solar cells by green solution-process

The highest efficiencies for both rigid and flexible Cu2ZnSn(S,Se)4 (CZTSSe) solar cells are still far behind the theoretical values. This is mainly due to band tailing in absorber and a large recombination near absorber/Mo interface that block the carrier transportation and lead to Voc and FF degradation, which are mostly noticeable in flexible solar cells. In this paper, CZTSSe thin films were prepared on flexible Mo substrates by green solution-based method followed by selenization. By optimizing selenization conditions (selenization time and temperature), dense and well crystallized CZTSSe thin films without micro-cracks were obtained at 550 °C for 12 min. The best efficiency of 6.78% can be achieved with Voc and FF enhanced to 390.43 mV and 57.71%. The dramatic reductions in ideal factor A, series resistance RS, the mismatch Δ(Eg-PL) and potential fluctuation γ indicate that band tailing and recombination are significantly reduced. The performance degradation with bending radius and cycles is studied for the first time among CZTSSe solar cells. Results indicate long-term stability at repeatable release–stretch cycles. The flexible CZTSSe solar cells with high stretch ability shed light on the development of flexible solar cells.

Research on the Development of Flexible Solar Cells

Research on the Development of Flexible Solar Cells

Light Management in Flexible Thin-Film Solar Cells—The Role of Nanoimprinted Textures and Tilted Surfaces

We present the application of ultraviolet (UV) nanoimprint lithography for the replication of advanced light management schemes in flexible thin-film solar cells. The approach is maintained entirely at low temperatures, which are required for the development of flexible solar cells on low-cost transparent polymer films. Light-scattering properties are significantly improved by this technique, and thin-film silicon solar cells prepared on these substrates show a substantial improvement in performance due to the nanoimprinted texture. We further investigate the effect of various incident angles of the light on the short-circuit current density (J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sc</sub> ) of the solar cell and evaluate the corresponding performance of a flexible solar cell in a bent state. Our results show that in the case of imprinted texture, the J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sc</sub> and efficiency is reduced within 5% in a bent case of a semicircle when a reduction of the effective illumination area with angle is not taken into account. Overall, the solar cell on imprint-textured polyethylene terephthalate (PET) film shows an increased J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sc</sub> for the entire range of incident angles and bent states compared with the nonimprinted PET substrate.

Flexible photovoltaic technologies

Flexible photovoltaic (PV) devices have attracted enormous attention from academy and industry as a convenient alternative energy source for indoor and outdoor applications. Flexible PV panels can be easily integrated with infrastructures of various shapes and sizes, meanwhile they are light-weight and thus suitable for applications where weight is important. In this review, we will describe the progress that has been made in the field of flexible PV technologies. In addition, a summary will be provided with perspective on the future development of flexible solar cells and new opportunities offered by these devices.

Effective piezo-phototronic enhancement of solar cell performance by tuning material properties

Piezo-phototronic effect is demonstrated in the ZnO/P3HT solar cell system and detailed study is conducted regarding the influence of crystallization and doping level of ZnO on the strength of piezo-phototronic effect as well as the overall solar cell performance. By testing and comparing five groups of samples prepared under different conditions, optimized parameters are determined for the most efficient piezo-phototronic enhancement of solar cell performance. The general principles and regularities provided in this study are universal and applicable to all solar cell systems involving piezoelectric semiconductor materials and could provide substantial guidance on further increasing performances of commercial solar cells based on CdTe, GaAs etc. and also spur the development of flexible solar cells for smart applications in various situations.

Development of high efficiency flexible solar cells

Elemental technological challenges required for the development of flexible solar cells have been clarified and a consortium system to solve the problems has been established based on industry-academia-government collaboration. The technology to form texture on polymer substrates indispensable for high efficiency has been developed, and we have succeeded in preparation of thin-film silicon solar cells on polymer substrates whose efficiency is comparable with that of cells prepared on glass substrates. The stage has already moved from research within the consortium to practical realization research in individual enterprises. Establishment process, management policy, patent strategy and training of young researchers of the consortium are described in this paper.