The fingerprint of charge transport mechanisms on the incident photon-to-current conversion efficiency spectra of perovskite solar cells

Abstract

Perovskite solar cells (PSCs), the most promising nanostructured solar cells for large-scale production, have been fabricated with different types of electron and hole collectors to improve efficiency and stability. Incident photon-to-current conversion efficiency (IPCE) is an important measurement to evaluate the optical/electrical behavior of the structure to modify the device structure. In this research, we have investigated how different mechanisms affect the IPCE spectra and the difference between short-circuit current density (Jsc) recorded from the current density-voltage (J-V) and the IPCE curves of n-i-p PSCs. Results show that by removing the electron-transport layer (ETL) in a device with a compact PSK layer, the IPCE spectrum does not change and only a slight shift of interference peak position is observable. By removing the hole-transport layer (HTL), not only IPCE value drops substantially for all wavelengths, its shape (including interference peaks) deforms significantly in the 500–800 nm wavelength range. In the case of cells with imperfect HTLs, only a slight change in this range (not the blue range) is observable. Utilizing different charge-transport and PSK materials, we have shown how significant the nonlinearity of the device's characteristics (such as charge-transfer resistance) with light intensity increases in the difference between Jsc value from J-V and integrated Jsc from IPCE curves. Selecting charge-collecting layers also directly affect interference peaks in IPCE spectra, for instance using TiO2 nanograss as ETL or CuIn0.75Ga0.25S2/carbon hole-collector instead of Spiro OMeTAD/Au hole-collector results in disappearing interference peaks.