Elucidating the Impact of Charge Selective Contact in Halide Perovskite through Impedance Spectroscopy

Abstract

paved the way for new formulations by the means of compositional engineering of perovskites. [1] Tweaking of halide anion and/or organic cation allowed to push the efficiency as well as stability. [2] Power conversion efficiencies as high as 25.2% have been reported at laboratory scale, [3] which is on par with other matured thin film photovoltaics (PV) technologies. The realization of perovskite for PV application was due to its intriguing optoelectrical properties, which led to its exploitation in other optoelectrical devices such as lasing, [4] X-ray, OLEDs, [5] and photodiodes. [6] Despite its unparalleled performance, the perovskites solar cells (PSCs) suffer from several key issues such as anomalous J-V hysteresis, electrical instability, nonradiative recombination losses, and environmental instability. The primary cause for J-V hysteresis is intrinsic defects present in the perovskites layers and charge accumulation at interfaces. [7][8][9][10] The plausible reason for the charge accumulation at the interface can be unbalanced electron and hole mobility which allows charge to be accumulated at the perovskite/electron selective contact (ESC) and perovskite/hole selective contact (HSC) interface. [11] In the past we have reported unbalance charge extraction along with its charge injection on time scale and noted charge accumulation at ESC/perovskite interface. [12] The defect states present in the bulk of perovskite effect the charge accumulation near the interface. Furthermore, the presence of defects in the bulk of perovskites further acts as trapping center for charge carriers, which in turn causes nonradiative losses and decreases charge carrier's lifetimes leading to deterioration in the device performance. Moreover, the presence of inorganic part suggests mixed conductivity, with contribution from both electronic and ionic conductivity. The ion migration was also speculated to be one of the reason for low long-term PV behavior under stress condition or at V oc . [13,14] Similarly cathode materials such as silver or gold were reported to be found at anode side, which travelled all the way through hole transport materials and perovskites. This diffusion of metallic contact into the active material is a loss and this process can activate intensely by thermal process. [15] Apart from all these, the undesirable process in which dopant ions mainly Li + (used in HSC) can diffuse The electron and hole selective contact (SC) plays a pivotal role in the performance of perovskite solar cells. In order to separate the interfacial phenomenon from bulk, the influence of charge SC is elucidated, by means of impedance spectroscopy. The specific role played by TiO 2 and Spiro-OMeTAD as electron and hole SC in perovskite solar cells is investigated at short circuit condition at different temperatures. The methylammonium lead triiodide (MAPbI 3 ) and mixed perovskite of formamidinium lead iodide and methylammonium lead bromide namely; (FAPbI 3 ) 0.85 (MAPbBr 3 ) 0.15 are probed and parameters such as charge carrier mobi...

Electrochemical Impedance Spectroscopy Analysis of Hole Transporting Material Free Mesoporous and Planar Perovskite Solar Cells

“…Moreover, the FF also decreases due to the higher R s value in the absence of HTM. Similarly, Khan et al [68] also performed a study on the impact of HTM layer in PSCs by EIS technique which also showed a lower recombination resistance in the case of HTM-free PSC devices.…”

Interface Engineering by Thiazolium Iodide Passivation Towards Reduced Thermal Diffusion and Performance Improvement in Perovskite Solar Cells

“…From the derivative of the capacitance spectrum (Figure S16, Supporting Information), we determined the frequency of peak emission ( f peak ) rate of electrons from a trap state located below E T to the LUMO edge E LUMO as depicted schematically in Figure . From the slope of Arrhenius plot, , the value of activation energy E A , and attempt to escape frequency υ 0 were deduced through the relation:38 where β is a proportionality constant, T is the temperature, and k B is the Boltzmann constant. The calculated activation energy for each device are presented in Table 1 .…”

“…From the slope of Arrhenius plot, ln . 1 peak 2 f T vs T , the value of activation energy E A , and attempt to escape frequency υ 0 were deduced through the relation: [38] ln ln…”

Interface Engineering by Thiazolium Iodide Passivation Towards Reduced Thermal Diffusion and Performance Improvement in Perovskite Solar Cells

“…, the value of activation energy EA, and attempt to escape frequency 0 were deduced through the relation: [38]  …”