Heterogeneous Supersaturation in Mixed Perovskites

Abstract

Thin-film solar cells based on hybrid lead halide perovskites have achieved certified power conversion efficiencies exceeding 24%, approaching those of crystalline silicon. This motivates deeper studies of the mechanisms that determine their performance. Twin defect sites have been proposed as a source of traps in perovskites, yet their origin and influence on photovoltaic performance remain unclear. It is found that twin defects-observed herein via both transmission electron microscopy and X-ray diffraction-are correlated with the amount of antisolvent added to the perovskite and that twin defects in the highest-performing perovskite photovoltaics are suppressed. Heterogeneous supersaturation nucleation is discussed as a contributor to efficient perovskite-based optoelectronic devices.

Keywords: defects; perovskites; traps; twins.

Figure 1

Scanning electron microscopy, film roughness, X‐ray diffraction, and UV–vis absorption spectrum of perovskites with different antisolvent treatments. SEM images of perovskites treated with a) 100, b) 200, c) 300, d) 400, and e) 500 µL of chlorobenzene antisolvent. f) RMS roughness. g) UV–vis absorption of perovskite thin films treated with different CB amounts.

Figure 2

Twin defects and strain in perovskites treated with 200 and 500 µL of antisolvent. High‐resolution TEM images of perovskites treated with a) 200 and e) 500 µL of antisolvent. b,f) (111) filtered images of (a) and (e), respectively. c,g) FFT of (a) and (e), respectively. Perovskite films treated with 500 µL of antisolvent show twin defects while those treated with 200 µL do not. d,h) Normalized strain tensor (ε_xy) distributions calculated from images (a) and (e), respectively. Color contour is showing the calculated values of the normalized strain tensor. i) The absolute value of the strain tensor (ε_xy)_max took at different observation points for perovskite films treated with 200 and 500 µL of antisolvent. j) High‐dynamic‐range EQE. Error bars represent the standard deviation in the measurements of perovskite thin films treated with different antisolvent amounts.

Figure 3

(100) X‐ray diffraction, photoluminescence, solar cell cross‐section, and photovoltaic characteristics. a) (100) XRD peak. b) Distortion of the (100) d spacing for perovskites treated with different amounts of antisolvent. c) Illustration the deformation of the (100) d spacing by the (111) twin plane. d) PL spectra. e) Time‐resolved PL. f) The cross‐section SEM image of the device. g) V _OC, h) PCE, and i) steady‐state power output of photovoltaic devices with perovskites treated with different amounts of antisolvent.