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

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 sig-nificant 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 dis-appearing interference peaks.