Page 244 - A Comprehensive Guide to Solar Energy Systems

Chapter 11 • Hybrid Organic–Inorganic Metal Halide Perovskite Solar Cells 247

planar devices can be reduced by passivating the surface defects of the perovskite layer
with treatments of pyridine or thiophene [111]. Surprisingly, hysteresis was not observed
for inverted planar perovskite solar cells based on PEdOT:PSS/perovskite/PC 60 BM with
high efficiencies [85,111,137]. However, substantial J–V hysteresis was observed when the
temperature of hysteresis-free inverted planar solar cells was reduced to 175 K [138] or
when the devices were older than a week [133]. From the discussion, we conclude that
hysteresis in perovskite solar cells does not depend on the type of device architecture, but
it can be minimized by improving the stability of the perovskite and the engineering of the
interfaces. The device cross-sectional imaging and corresponding J–V characteristics of
perovskite solar cells showing hysteresis behavior are presented in Fig. 11.7 [136].

11.6 Summary

The film formation process of perovskite plays a critical role in determining device perfor-
mances. Perovskite thin films can be prepared by various techniques; the main techniques
include one-step solution, two-step sequential deposition processes, vapor deposition, and
vapor assisted solution processing. The perovskite film morphology is crucially important
for device performance. It can be optimized by various approaches such as the use of addi-
tives, thermal annealing, solvent annealing, atmospheric control, and solvent engineering.
during film fabrication, control over crystallization, and growth of perovskites is required
to achieve uniform film with full surface coverage, large crystal size, and even good stabil-
ity. Improved processing of film fabrication with proper morphological control has already
created great success in perovskite PV, and it is believed that this will lead to a significant
breakthrough in developing useful and successful perovskite solar cells in the future.
High performance solar cells are based on mesoporous oxide scaffolds because of
their good film quality. However, the high temperature annealing processes required in
mesoporous film formation increases processing complexity and cost. The fabrication of
perovskite solar cells using mesoporous structures might mitigate against the compatibil-
ity of implementing a high performance flexible product with the integration of tandem
cells into commercialized existing technologies. However, the planar device configura-
tion approach is considered an appropriate technological path for the fabrication of high
performance flexible solar cells. It is believed that numerous research efforts within the
perovskite PV community will, in the near future, solve the prevailing stability issues re-
sulting in the practical commercialization of perovskite solar cells.

References

[1] International Energy Outlook 2016. US Energy Information Administration, 2016.
[2] Schmela M: Global market outlook for solar power/2016-2020, Brussels, Belgium, 2016, Solar power
Europe.
[3] Bhandari KP, Collier JM, Ellingson RJ, Apul dS: Energy payback time (EPBT) and energy return on
energy invested (EROI) of solar photovoltaic systems: a systematic review and meta-analysis, Renew
Sust Energy Rev 47:133–141, 2015.