Understanding the Influence of Interface Morphology on the Performance of Perovskite Solar Cells

Abstract

In recent years, organo-halide perovskite solar cells have garnered a surge of interest due to their high performance and low-cost fabrication processing. Owing to the multilayer architecture of perovskite solar cells, interface not only has a pivotal role to play in performance, but also influences long-term stability. Here we have employed diverse morphologies of electron selective layer (ESL) to elucidate charge extraction behavior in perovskite solar cells. The TiO2 mesoporous structure (three-dimensional) having varied thickness, and nanocolumns (1-dimensional) with tunable length were employed. We found that a TiO2 electron selective layer with thickness of about c.a. 100 nm, irrespective of its microstructure, was optimal for efficient charge extraction. Furthermore, by employing impedance spectroscopy at different excitation wavelengths, we studied the nature of recombination and its dependence on the charge generation profile, and results showed that, irrespective of the wavelength region, the fresh devices do not possess any preferential recombination site, and recombination process is governed by the bulk of the perovskite layer. Moreover, depending on the type of ESL, a different recombination mechanism was observed that influences the final behavior of the devices.

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

“…In LF region (20 Hz-1 kHz) capacitance decreases with frequency and is temperature dependent. [44][45][46][47] The devices fabricated with mixed perovskite showed similar trend, suggesting low frequency behavior is related to interfacial properties rather than bulk. The stable plateau in IF range corresponds to dielectric relaxation in the perovskites layer and determined by the geometrical capacitance per unit area C g = εε 0 /L, where ε is dielectric constant of perovskite, ε 0 is the vacuum permittivity, and L is the layer thickness.…”

“…[12,47] All solutions were prepared inside an argon glove box under controlled moisture and oxygen conditions (H 2 O level: <1 ppm and O 2 level: <10 ppm). Substrates were cleaned by ultrasonication in three different solutions with the aim to eliminate any possible contamination.…”

Stability and Performance of Nanostructured Perovskites for Light‐Harvesting Applications

“…Perovskite solar cells (PSCs) and light harvesting devices (PLHDs) in general, can roughly be grouped into thin film (TF‐) PSCs of varying thicknesses, depending on the optical properties and charge carrier diffusion length of the used perovskite, and structured PLHDs which can be further distinguished according to the typical length scales of the used structures . Structured devices can be divided into one of two length scales: mesoscopic, or because of the poplar usage of mesoporous titanium oxide often also denoted mesoporous (mp), and nanoscopic or often also called nanostructured due to the use of nanostructures with controllable geometry …”

“…Additional to grouping PSCs or PLHDs according to their length scale, it is useful to take the type of structure into account since there are multiple approaches to meso‐ and nanostructuring that can be grouped into the use of structured contact‐ or scaffold‐materials . Options include scaffolds that can be covered by perovskite nanocrystals or completely infiltrated/covered by the used perovskite, thereby embedding the contact materials . Alternatively, nanostructuring the perovskite itself is often realized using an anodic‐aluminum‐oxide (AAO) scaffold as a template .…”

“…The distinction between contact and scaffold material is based on the fact whether or not the energy bands align close enough to make charge carrier injection from the photoactive material into the contact/scaffold possible or not (see Figure ). The materials used for structured contacts are usually n‐ or p‐type transparent oxides such as TiO 2 and ZnO for p–i–n solar cells or NiO for n–i–p solar cells, while transparent nonconductive oxides such as Al 2 O 3 and ZrO 2 are used as templates or scaffolds . The structuring can be achieved by a variety of methods.…”