Abstract
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.
Highlights
The unique flexibility and lightweight characteristics of flexible solar cells render its applicability on various electronic devices to obtain continuous energy.[1−5] In contrast to the rigid substrate of conventional solar cells, the flexible solar cells are bendable or stretchable and can adapt to the various environmental conditions by altering its shape
As portrayed by the internal quantum efficiency (IQE) results (Figure 3G), the tapered MW-based flexible c-Si solar cells exhibited an extremely high IQE of over 95% at the wavelength range of 300−700 nm. This is because a majority of the relatively short wavelength light was absorbed by the tapered MWs, and the generated photo carriers were efficiently collected through the radial junction of the tapered MWs
The light absorption capability of thin c-Si films was enhanced with 1) vertical c-Si MW arrays formed onto flexible thin c-Si film and 2) random invertedpyramidal (RIP)-PDMS optical films for planar flexible c-Si solar cells
Summary
The unique flexibility and lightweight characteristics of flexible solar cells render its applicability on various electronic devices to obtain continuous energy.[1−5] In contrast to the rigid substrate of conventional solar cells, the flexible solar cells are bendable or stretchable and can adapt to the various environmental conditions by altering its shape. The development of flexible solar cells can create new values in various industries such as IT, display, electric vehicle, and aerospace, which require the use of solar cells on curved or uneven surfaces.[6] In recent years, the development of perovskite-based flexible solar cells has significantly improved the power conversion efficiency (PCE) because of the superior light absorption and electrical properties exhibited by the perovskite materials.[3,4] the thin-film-based flexible solar cells such as organic and perovskite solar cells still pose a critical problem pertaining to low material stability.[7,8] In particular, the photoactive materials of the perovskite solar cells, such as methylammonium lead iodide, are highly unstable toward moisture and can result in the decomposition of the perovskite structure.
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