Light-Induced Space-Charge Accumulation Zone as Photovoltaic Mechanism in Perovskite Solar Cells

Abstract

We fabricated formamidinium lead iodide perovskite solar cell for analysis of the photovoltaic mechanism based on the interpretation of the capacitance variation under illumination. It was shown that the low frequency capacitance increases proportional to incident light intensity, and in addition it increases proportional to absorber thickness. Furthermore the voltage dependence of capacitance is exponential with slope 1/2kT. We conclude that the large photovoltage and capacitance are associated to electronic accumulation zone at the interface with the metal oxide contact. While this type of accumulation capacitance is common in many devices as transistors, the perovskite solar cell shows a singular behavior in that under light, the electronic carrier accumulation grows unlimited by another series capacitance, reaching values as large as 10 mF cm -2 at one sun illumination.

Tunable hysteresis effect for perovskite solar cells

“…7 provides a picture of the charge accumulation and polarization features at the interface. The formation of an accumulation of cations and electronic holes at the c-TiO 2 /perovskite interface under illumination has been discussed 42 and is shown in Fig. 7c.…”

Investigating the Consistency of Models for Water Splitting Systems by Light and Voltage Modulated Techniques

“…It should be noted that Equation 7 will only be valid for illumination intensities which assure the formation accumulation zone. It is known from previous analysis 18 that it generally occurs for oc V ≥ 0.4-0.5 V above which the photovoltage is held by the electrostatic potential built-up at the interface.…”

“…[13][14][15][16] The analysis and mechanism identification of capacitive elements have raised certain attention in the last few years concluding that perovskite dielectric processes and interfacial charge accumulation dominate at the high-and lowfrequency response, respectively. [17][18] However the detailed classification of the resistances seems to be particularly elusive. This is a central point for device understanding in so far as the dc behavior (and consequently the steady-state V J − curve and efficiency) of the photovoltaic device is determined by the internal resistances.…”

“…s C appears as a consequence of interface accumulation processes, either of ionic character in the dark, or electronic under illumination. 18 Although several studies have discussed the origin of the different electrical features of the perovskite solar cells, the lack of a complete model, including resistive elements, prevents a full understanding of how these circuit elements define the performance of the cells. Here we aim at progressing in the understanding of the resistive mechanisms that ultimately establish the steady-state response of the V J − curves.…”

“…C has been interpreted in terms of the light-induced built-up of an electronic accumulation zone formed by majority carrier (holes) in the vicinity of the cathode contact (TiO 2 /perovskite interface). 18 The model in Figure 3 accounts for the cathode contact in open circuit conditions. The accumulation layer corresponds to an upward band bending zone with extension equaling the Debye length of the background hole density 0 p as …”