Suppression of Hysteresis Effects in Organohalide Perovskite Solar Cells

Abstract

Thin‐film solar cell based on hybrid perovskites shows excellent light‐to‐power conversion efficiencies exceeding 22%. However, the mixed ionic‐electronic semiconductor hybrid perovskite exhibits many unusual properties such as slow photocurrent instabilities, hysteresis behavior, and low‐frequency giant capacitance, which still question us so far. This study presents a direct surface functionalization of transparent conductive oxide electrode with an ultrathin ≈2 nm thick phosphonic acid based mixed C60/organic self‐assembled monolayer (SAM) that significantly reduces hysteresis. Moreover, due to the strong phosphonates bonds with indium tin oxide (ITO) substrates, the SAM/ITO substrates also exhibit an excellent recyclability merit from the perspective of cost effectiveness. Impedance studies find the fingerprint of an ion‐based diffusion process in the millisecond to second regime for TiO2‐based devices, which, however, is not observed for SAM‐based devices at these low frequencies. It is experimentally demonstrated that ion migration can be considerably suppressed by carefully engineering SAM interfaces, which allows effectively suppressing hysteresis and unstable diode behavior in the frequency regime between ≈1 and 100 Hz. It is suggested that a reduced density of ionic defects in combination with the absence of charge carrier accumulation at the interface is the main physical origin for the reduced hysteresis.

On the Current–Voltage Hysteresis in Perovskite Solar Cells: Dependence on Perovskite Composition and Methods to Remove Hysteresis

“…Between TiO 2 and perovskite an ultrathin SAM (self‐assembled monolayer) was inserted to reduce the hysteresis. As can be seen in Figure , hysteresis disappears by insertion of a C 60 ‐based SAM between TiO 2 and MAPbI 3 in normal planar structure . Impedance studies revealed that capacitance of the C 60 ‐SAM‐based devices showed about two orders of magnitude smaller at low and medium frequencies than that of the TiO 2 ‐based devices, which underlines that ionic defect density at interface was significantly reduced by insertion of interlayer.…”

“…In normal structure, TiO 2 and spiro‐MeOTAD are chosen for investigation because they were mostly employed for PSCs. Figure shows some of selected J – V curves of the device employing MAPbI 3 in normal mesoscopic device structure including c‐TiO 2 , mp‐TiO 2 . Although kink structure of the forward scanned J – V curves and small deviation in V oc are sometimes detected, almost no change in J sc and V oc between reverse and forward scan is observed as common feature in the normal mesoscopic structure of FTO/c‐TiO 2 /mp‐TiO 2 /MAPbI 3 /spiro‐MeOTAD/Au.…”

“…SAM was composed of C 60 with 30% of C 60 ‐C 6 ‐PA (PA = phosphoric acid). All panels reproduced with permission …”

“…For the surface or structural modification of selective contacts, TiO 2 doped with lithium ion exhibited hysteresis‐less behavior . In addition, other ions such as indium, sodium, niobium and transition metal ions were used to modify surface or defect of TiO 2 , which reduced nonradiative recombination in perovskite near TiO 2 and thereby hysteresis was substantially reduced. The CsX (X = I and Br) doped mesoporous TiO 2 was found to show no significant hysteresis as compared to the bare TiO 2 , which was attributed to less charge accumulation at perovskite/CsX‐doped TiO 2 interface .…”

Interfacial Engineering of Metal Oxides for Highly Stable Halide Perovskite Solar Cells

“…Research on different interfacial organic modifiers has gained attention due to their ability to influence oxide properties, tune their electrical, chemical, and physical properties, affect charge carrier dynamics (transport, injection, and recombination) or modify their work function. Other benefits of applying surface modifiers in PSCs are, for example, the enhancement of moisture tolerance, the suppression of hysteresis, the enhancement of power conversion efficiency, and lifetime stability; moreover, the enhancement of the fracture resistance of perovskite films can be reinforced with the aid of organic or polymeric modifiers …”