Fig. 1. (Color online) Three-dimensional (3D) nanostructured silicon solar cells and their corresponding absorption spectra. (a1, a2) Double-sided nanostructure. (b1, b2) Top-only nanostructure. (c1, c2) Bottom-only nanostructure. (d1, d2) Flat film. Red curves stand for the Yablonovitch limit, green curves are the single-pass absorption spectra, and black curves represent spectra for corresponding structures. Reproduced with permission^[31]. Copyright 2014, Wiley-VCH.

Fig. 2. The scanning electron microscope (SEM) of inverse nanocone (NC) template (a) and NC arrays (b). (c) The external quantum efficiency (EQE) spectra of CdTe solar cells with and without NC film. The inset of (c) is the schematic structure of the device. (a–c) Reproduced with permission^[25]. Copyright 2014, Wiley-VCH. (d) SEM of NC arrays. The inset is a drop of water on NC arrays, illustrating a contact angle of 155°. (e) The current density–voltage (J–V) characteristics of perovskite solar cells with and without NC arrays (inset is a photo of the flexible device). (f) Under different incident angles, the short-circuit current density (J_sc) and the power conversion efficiency (PCE) with and without NC arrays. (d–f) Reproduced with permission^[38]. Copyright 2015, American Chemical Society. (g) Schematic procedure of 3D nanostructured a-Si:H solar cells. (1) Spin coating ZnO film on polyimide film. (2) Patterned ZnO film. (3) A a-Si:H solar cell constructed on the as-fabricated substrate. (4) Fabrication of nanoindentation on aluminum foils. (5) The anodic aluminum oxide (AAO) template with inverse NC arrays. (6) The NC arrays film peeled off from the template. (7) The a-Si:H solar cell with nanostructured back-reflector and top anti-reflection NC arrays. (h) Normalized PCE under different bending angles. (i) Normalized PCE as a function of bending cycles. The insets (h) and (i) demonstrate bending angles and a bent solar cell mounted on the set-up. Reproduced with permission^[39]. Copyright 2017, Wiley-VCH.

Fig. 3. (Color online) (a) Complete compound moth eyes and a moth-eye-inspired structure (MEIS) device structure diagram. (b) Reflectance spectra of MEIS and human luminosity curve, inset is the photo of MEIS (scale bars, 3 cm). (c) J–V curves of the MEIS ST-PSCs and a planar reference under simulated AM1.5G illumination, the inset is the photographs of (c) (scale bars, 2 cm). Reproduced with permission^[50]. Copyright 2021, Wiley-VCH. (d) SEM images of TiO₂ nanobowl with a diameter of 180 nm (NB-180). (e) J–V curves of the device based on different diameters. (f) Simulated cross-sectional |E| distribution of the electromagnetic (EM) waves at 600 nm wavelength in the perovskite deposited on (f1) TiO₂ NB-180, (f2) TiO₂ NB-220, (f3) TiO₂ NB-500, and (f4) planar TiO₂, Reproduced with permission^[21]. Copyright 2021, Wiley-VCH. (g) Schematic view of nanostructured a-Si:H thin-film. (h) SEM image of the 100 nm Ag-coated substrates deposited with 100 nm conductive Al-doped ZnO (AZO). (i) The calculatedJ_sc of the device based on different diameters TiO₂. (j) Normalized PCE under different bending angles. The inset (j1) represents a photo of the measurement set-up and (j2) a schematic of bending angles. Reproduced with permission^[40]. Copyright 2021, Wiley-VCH.

Fig. 4. (Color online) (a) Cross-sectional schematic diagram of a 3D solar nanopillar cell, demonstrating improved carrier separation and collection. (b) SEM images of d a CdS nanopillar array. The experimental (c) and simulated (d) absorption spectra of the nanowire (NW) plotted as a function of diameter and pitch. (c, d) Reproduced with permission^[15]. Copyright 2012, American Chemical Society. (e) SEM images of InSb NW. (f) The electron mobility of InSb NW. (e, f) Reproduced with permission^[58]. Copyright 2019, American Chemical Society. (g) Visualization of the Shockley–Read–Hall (SRH) recombination in the 3D nanopillar cells plotted with a function of heigh (H): H = 0 nm (g1) and H = 900 nm (g2). (a, b, g) Reproduced with permission^[28]. Copyright 2009, Nature Research. (h) Schematic representation of BiI₃ structure. (h) Reproduced with permission^[75]. Copyright 2017, Wiley-VCH. (i) Cross-sectional schematic diagram of 3D BiI₃ nanosheets (NSs) cell. (j) SEM of BiI₃ NSs. (k) J–V curves of BiI₃ NSs solar cells from different precursor Bi thicknesses. (i–k) Reproduced with permission ^[22]. Copyright 2020, Wiley-VCH.

Fig. 5. (Color online) (a) Schematic diagram of the 3D nanospike. (b) Angular and wavelength-dependent absorption of a nanospike solar cell and a planar reference. (c) Normalized PCE of the nanospike device under different bending angles, inset is the schematic of a flexible nanospike solar cell. (a–c) Reproduced with permission^[52]. Copyright 2014, The Royal Society of Chemistry. (d) SEM image of a-Si:H solar cells on 0.5 aspect ratio nanocone. The aspect ratio is the ratio between height and pitch. Simulated cross-sectional stress distribution of flat (e) and nanocone devices (f), with their photos after bending with a radius of 4 mm shown. (d–f) Reproduced with permission^[73]. Copyright 2016, The Royal Society of Chemistry.