Stretchable and colorless freestanding microwire arrays for transparent solar cells with flexibility

Sung Bum Kang,Chil-Min Kim,Myeong Hoon Jeong,Chan Ul Kim,Ji-Hwan Kim,Kyoung Jin Choi,Amit Sanger

doi:10.1038/s41377-019-0234-y

Abstract

Transparent solar cells (TSCs) are emerging devices that combine the advantages of visible transparency and light-to-electricity conversion. Currently, existing TSCs are based predominantly on organics, dyes, and perovskites; however, the rigidity and color-tinted transparent nature of those devices strongly limit the utility of the resulting TSCs for real-world applications. Here, we demonstrate a flexible, color-neutral, and high-efficiency TSC based on a freestanding form of n-silicon microwires (SiMWs). Flat-tip SiMWs with controllable spacing are fabricated via deep-reactive ion etching and embedded in a freestanding transparent polymer matrix. The light transmittance can be tuned from ~10 to 55% by adjusting the spacing between the microwires. For TSCs, a heterojunction is formed with a p-type polymer in the top portion of the n-type flat-tip SiMWs. Ohmic contact with an indium-doped ZnO film occurs at the bottom, and the side surface has an Al2O3 passivation layer. Furthermore, slanted-tip SiMWs are developed by a novel solvent-assisted wet etching method to manipulate light absorption. Finite-difference time-domain simulation revealed that the reflected light from slanted-tip SiMWs helps light-matter interactions in adjacent microwires. The TSC based on the slanted-tip SiMWs demonstrates 8% efficiency at a visible transparency of 10% with flexibility. This efficiency is the highest among Si-based TSCs and comparable with that of state-of-the-art neutral-color TSCs based on organic–inorganic hybrid perovskite and organics. Moreover, unlike others, the stretchable and transparent platform in this study is promising for future TSCs.

Highlights

Transparent solar cells (TSCs) are emerging as building blocks for building-integrated power generation[1,2,3,4]
A 15-nm-thick Al2O3 layer was deposited on the silicon microwires (SiMWs) by atomic layer deposition (ALD) to passivate the Si surface
The photovoltaic parameters of the device in Stretchability of the Si microwire array polymer composite film (SiMPF) platform and its application for stretchable solar cells As shown in Fig. 5a, the optical diffraction patterns are produced by transmitted light, demonstrating the Fourier transform properties between the reciprocal domains

Summary

Introduction

Transparent solar cells (TSCs) are emerging as building blocks for building-integrated power generation[1,2,3,4]. In this attractive concept of photovoltaics, there is an unavoidable trade-off between the energy generation (i.e., the photovoltaic conversion efficiency (PCE)) and the light admission (visible transparency). The most common way to develop transparent solar cells is via band-gap engineering of active materials that can absorb sunlight selectively, resulting in tinted transparency[5,6,7,8,9]. Previous attempts have been made to develop transparent solar cells by taking advantage of dyes as active materials When the active layers are designed to absorb short-wavelength light and transmit longwavelength light in the visible range (λ > 600 nm), the transparent devices exhibit a yellow or reddish color[7,8,9,10,11,12,13,14].

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Conclusion