Negative Capacitance and Inverted Hysteresis: Matching Features in Perovskite Solar Cells

Abstract

Negative capacitance at the low-frequency domain and inverted hysteresis are familiar features in perovskite solar cells, where the origin is still under discussion. Here we use Impedance Spectroscopy to analyse these responses in methylammonium lead bromide cells treated with lithium cation at the electron selective layer/perovskite interface and in iodide devices exposed to different relative humidity conditions. Employing the Surface Polarization Model, we obtain a time constant associated to the kinetics of the interaction of ions/vacancies with the surface, τkin, in the range of 10 0 -10 2 s for all the cases exhibiting both features. These interactions lead to a decrease in the overall recombination resistance, modifying the low-frequency perovskite response and yielding to a flattening of the cyclic voltammetry. As consequence of these results we find that that negative capacitance and inverted hysteresis lead to a decrease in the fill factor and photovoltage values.

In the Quest of Low‐Frequency Impedance Spectra of Efficient Perovskite Solar Cells

“…Recent studies by Alvarez et al, have shown that the faster time response or kinetics lead to a behavior dominated by ionic diffusion. [36] In the present case, faster ionic diffusion is expected in IPA-PSCs because of larger grains' sizes. This result signifies that the sizes of the grains affect the impedance response of PSCs.…”

“…The reduction in the capacitance values was previously observed after Li þ treatment of the TiO 2 layer. [36] The authors found that the presence of Li þ at ETL/perovskite interface could reduce the accumulation of the intrinsic ions, and especially avoid the interactions at ETL surface by reducing the density of holes. [36] In line with the results shown in Figure 2d, a higher value of R HF and R LF in TiO 2 /SnO 2 PSC is obtained as compared with that of the reference device, which suggests lower recombination and higher value of V OC (Figure 2f ).…”

“…[36] The authors found that the presence of Li þ at ETL/perovskite interface could reduce the accumulation of the intrinsic ions, and especially avoid the interactions at ETL surface by reducing the density of holes. [36] In line with the results shown in Figure 2d, a higher value of R HF and R LF in TiO 2 /SnO 2 PSC is obtained as compared with that of the reference device, which suggests lower recombination and higher value of V OC (Figure 2f ). In the case of TiO 2 /SnO 2 PSC, lower recombination is expected as charge accumulation at interface, i.e., C LF is lower than that found in TiO 2 PSC (Figure 2e).…”

Technology agnostic frequency characterization methodology for memristors

“…Furthermore, due to the nature of these devices, electrochemical redox processes are considered to be commonplace 9 , 10 . Other types of electrochemical processes, such as adsorption–desorption and diffusion, seen more commonly in similar solid state devices, such as, perovskite solar cells 11 , 12 , lithium-ion batteries 13 , fuel cells 14 , OLEDs 15 , Fe doped SrTiO3 (STO) thin films 16 , may also materialize inside memristors, due to the abundance of oxygen vacancies and other interstitials, thought to be the cause of the resistive switching phenomenon 17 . Many of these processes are better identified in an Alternating Current (AC) environment.…”

Toward a Scalable Fabrication of Perovskite Solar Cells under Fully Ambient Air Atmosphere: From Spin-Coating to Inkjet-Printing of Perovskite Absorbent Layer

“…According to the literature, the normal hysteresis presented in PSCs is attributed to the existence of a capacitive current before reaching the steady-state current, namely, there is an accumulation of charges in the forward scan ("capacitor filling") and a release of charges in the reverse scan ("capacitor emptying") [40]. On the other hand, the inverted hysteresis is intimately related to phenomena of negative capacitance, which are associated with surface interactions with vacancies/ions at the electron transport layer/perovskite interface [41]. A more and in-depth discussion on the origins of the obtained PV parameters variation is given in the following paragraphs through the quantum efficiency and impedance measurements on PSCs.…”