Page 243 - A Comprehensive Guide to Solar Energy Systems

246 A COMPREHENSIVE GUIdE TO SOLAR ENERGy SySTEMS

11.5.2 J–V Hysteresis

Standard solar cells such as CdTe and Si, do not change the nature of the current density–
voltage (J–V) curves while scanning from forward bias to reverse bias voltage and vice
versa, but perovskite solar cells display anomalous J–V hysteresis phenomenon [130]. The
variation in J–V characteristics depends on the direction and the rate of the voltage sweep.
This lack of accuracy in J–V measurement poses a great concern in scientific community
as it leads to inaccurate device efficiencies. The origin of hysteresis is still open for discus-
sion although ferroelectricity [131,132], ion migration [133,134], and unbalanced charge
collection rates [135] have been proposed as possible reasons. The application of mesopo-
rous TiO 2 considerably weakens the hysteresis effects, while the equivalent planar devices
struggle with severe hysteresis due to the induce dipole polarization in perovskite films as
shown in Fig. 11.7 [44,130,136]. However, the degree of hysteresis depends on the thick-
ness of the mesoporous TiO 2 layer [130]. The charge transfer between the perovskite and
planar TiO 2 is not efficient in comparison with mesoporous TiO 2 layer. The hysteresis in

FIGURE 11.7 SEM Cross-sectional images of mesoporous structured solar cells with (A) 220 nm, (B) 110 nm thick
mp-TiO 2 , (C) planar structured solar cell without mp-TiO 2 . J–V characteristics measured at forward bias scan (FS) and
reverse bias scan (RS) for mesostructured devices, (D) 220 nm, (E) 110 nm thick mp-TiO 2 , and (F) planar structured solar
cell without mp-TiO 2 . The solar cells were illuminated with AM1.5G illumination at a voltage setting time of 200 ms.
Adapted with permission from Kim H-S, Park N-G. Parameters affecting I–V hysteresis of CH 3 NH 3 PbI 3 perovskite solar
cells: effects of perovskite crystal size and mesoporous TiO 2 layer. J Phys Chem Lett 2014;5:2927–9, copyright 2014,
American Chemical Society.