Lead-free and electron transport layer-free perovskite yarns: Designed for knitted solar fabrics

Highly flexible and Lead-free perovskite solar yarns, based on methylammonium tin mixed halide Polyvinylpyrrolidone (PVP) composite nanofibers doped with [6,6]-Phenyl C61 butyric acid methyl ester (PC61BM), as the light harvesters are reported. The photoactive nanofiber layer of the solar yarn featured an optical bandgap of 1.65 eV, with a remarkable light absorption capacity > 90% in the wavelength range of 300-550 nm, outstanding flexibility, and an impressive charge carrier lifetime of 278 ns which rises to 300 ns upon doping with PC61BM. These photoactive nanofibers are directly electrospun on top of poly(3-hexylthiophene-2,5-diyl) 'P3HT', as the hole transporting layer, which was coated on a multi-filament carbon fiber yarn. The resulting yarn is twisted with a commercial silver yarn, serving as the positive electrode. The ensuing fiber-shaped solar device exhibits a maximum power conversion efficiency of 5.34% which is increased to 7.49% upon doping the photoactive layer with 0.17% PC61BM. A knitted solar fabric from the novel solar yarn with 45-mm x 35-mm active area presented a maximum power density of 1.21 mWcm(-2) under 1 sun (1000 Wm(-2)) solar illumination.