posted on 2018-03-20, 00:00authored byYen-Chen Shih, Leeyih Wang, Hsiao-Chi Hsieh, King-Fu Lin
Ion
accumulation of organometal halide perovskites (OHPs) induced by electrode
polarization of perovskite solar cells (PSCs) under illumination has
been intensely studied and associated with a widely observed current–voltage
hysteresis behavior. This work is dedicated to the investigation of
the behavior of charged species at the compact TiO2/OHP
interface with respect to electrode polarization in PSC devices. By
providing a comprehensive discussion of open-circuit voltage (VOC) buildup and VOC decay under illumination and in the dark for the PSCs modified with
[6,6]-phenyl-C61 butyric acid methyl ester (PCBM) at the
TiO2/OHP interface and their corresponding electrochemical
impedance spectroscopies (EISs), a justified mechanism is proposed
attempting to elucidate the dynamics of interfacial species with respect
to the time and frequency domains. Our results demonstrate that the
retarded VOC buildup and decay observed
in PSC devices are related to the formation of bound charges in TiO2, which is essential to neutralize the oppositely charged
ions accumulating at the OHP side. Besides, inserting a thicker PCBM
at the TiO2/OHP interface as a passivation layer can alleviate
the electrode polarization more efficiently as verified by the low
dielectric constant measured from EIS. Moreover, photoluminescence
measurements indicate that PCBM at the TiO2/OHP interface
is capable of passivating a trap state and improving charge transfer.
However, with respect to the time scale investigated in this work,
the reduction of the hysteresis behavior on a millisecond scale is
more likely due to less bound charge formation at the interface rather
than shallow trap-state passivation by PCBM. After all, this work
comprehensively demonstrates the interfacial properties of PSCs associated
with PCBM passivation and helps to further understand its impact on
charging/discharging as well as device performance.