Magneto‐Optical Studies on Spin‐Dependent Charge Recombination and Dissociation in Perovskite Solar Cells

Abstract

high photoexcitation intensity can lead to room-temperature magneto-photoluminescence and magneto-photocurrent with negative and positive signs, respectively, below the fi eld of 200 mT. Our results provide evidence that the charge recombination and dissociation are spin dependent at room temperature in OMHPs. Essentially, our results indicate that applying a magnetic fi eld can suppress the spin mixing between antiparallel and parallel spin states in electron-hole pairs and consequently decreases the antiparallel spin states but increases the parallel spin states. The change between different spin states in electron-hole pairs can eventually modify the exciton formation when the electron-hole pairs relax into excitons. Because of Pauli Exclusion Principle applied onto excitonic states, the singlet and triplet excitons can have high and low annihilation rates. As a result, decreasing the antiparallel spin states in electron-hole pairs by suppressing the spin mixing can weaken the singlet exciton formation, consequently leading to a decrease on photoluminescence toward the development of negative magneto-photoluminescence. On the contrary, decreasing the exciton formation can slow down the consumption on the electron-hole pairs. This can lead to more electron-hole pairs ready for charge dissociation to generate a photocurrent, generating a positive magneto-photocurrent. Clearly, the spin polarizations can be used as a new approach to control the charge recombination and dissociation in OMHPs. Furthermore, by using the observed magneto-photoluminescence and magneto-photocurrent, we investigate the dissociation effects in electron-hole pair states at different excitation intensities to further understand charge recombination and dissociation at different densities at device-operating condition. We fi nd that the critical bias required to completely quench the magneto-photocurrent and magneto-photoluminescence signals is increased with increasing photoexcitation intensity in OMHPs. This implies that, as the charge density increases with increasing the photoexcitation intensity, the formation of electron-hole pairs is enhanced, requiring a stronger fi eld to complete the charge dissociation toward generating photocurrent. Simultaneously, the line-shape on magneto-photocurrent and magnetophotoluminescence shows a narrowing phenomenon with increasing photoexcitation intensity. This indicates that the electron-hole pairs experience mutual inter-pair interactions and consequently changes the internal interactions within each electron-hole pairs. Clearly, our magneto-optical studies can provide critical understanding on controlling spin-dependent charge recombination and dissociation toward improving the photovoltaic actions in perovskite solar cells. Figure 1 a shows the magneto-photocurrents at different excitation intensities from the continuous wave (CW) laser beam of 532 nm in OMHP solar cells with the device architecture of ITO/PEDOT:PSS/CH 3 NH 3 PbI 3x Cl x /PC 71 BM/TiO x /Al. We Organometal halide perovskites (OM...

Rashba Spin–Orbit Coupling Enhanced Carrier Lifetime in CH3NH3PbI3

“…[58][59][60] Rashba SOC enhanced carrier lifetime highlights the potential of 3D Rashba materials 61 for photovoltaic applications. The ability to incorporate different organic molecules in OMHPs provides a robust avenue to design 3D Rashba materials.…”

Correction to Rashba Spin–Orbit Coupling Enhanced Carrier Lifetime in CH3NH3PbI3

“…Moreover, recent studies of carrier dyanmics under magnetic field also illustrate the significance of spin in carrier recombinations. [39][40][41] Rashba SOC enhanced carrier lifetime highlights the potential of 3D Rashba materials for photovoltaic applications. The ability to incorporate different organic molecules in OMHPs provides a robust avenue to design 3D Rashba materials.…”

Effective-mass model and magneto-optical properties in hybrid perovskites

“…A moderate magnetic field less than 1 T is found to be able to influence exciton PL in CH 3 NH 3 PbI 3 1112, indicating that magnetic field is a versatile tool for studying excitons and free carriers. This MFE has been attributed to the Δ g (the difference between electron and hole g -factors) mechanism, frequently encountered in organic radical pairs24.…”

“…The materials also exhibit many intriguing features, including strong spin-orbit coupling7 and the associated Rashba effect89, large-radius Wannier excitons10, and novel magnetic-field effect (MFE) in photoluminescence (PL) and photoconduction1112, and show promise in light-emitting13 and thermoelectric14 applications.…”