Fig. 1. Flowchart of SC preparation process

Fig. 2. Crystal seeding method for preparing BP. (a) Schematic of an annealing apparatus; (b) muffle furnace heating process

Fig. 3. Influence of seed crystal on the size of BP. (a)(c) NSC-BP sample and its enlarged view; (b)(d) SC-BP and its enlarged view

Fig. 4. Influence of the number of SCs on BP size. (a)-(c) Samples with number of SCs of 1, 2, and 3; (d) enlarged view of single-SC BP; (e) length of BP prepared with different numbers of SCs

Fig. 5. SEM and TEM images of SC-BP. (a)-(f) SEM images under different magnifications; (g)(h) low-resolution and high-resolution TEM images

Fig. 6. Phase structure of original BP and SC-BP. (a) Raman spectra of BP; (b) local enlarged-view of Raman spectra; (c) XRD spectra of BP; (d) local enlarged-view of XRD spectra

Fig. 7. Phase composition of original BP and SC-BP. (a) Element spectra of phosphorus; (b) full XPS spectra of BP

Fig. 8. Optical and electrical properties of BP. (a) Absorption spectra; (b) EIS

Fig. 9. Influence of excess Sn on BP. (a) BP prepared with excess Sn; (b) local magnification