Mechanism of Charge Transfer and Recombination Dynamics in Organo Metal Halide Perovskites and Organic Electrodes, PCBM, and Spiro-OMeTAD: Role of Dark Carriers

Abstract

Despite the unprecedented interest in organic-inorganic metal halide perovskite solar cells, quantitative information on the charge transfer dynamics into selective electrodes is still lacking. In this paper, we report the time scales and mechanisms of electron and hole injection and recombination dynamics at organic PCBM and Spiro-OMeTAD electrode interfaces. On the one hand, hole transfer is complete on the subpicosecond time scale in MAPbI3/Spiro-OMeTAD, and its recombination rate is similar to that in neat MAPbI3. This was found to be due to a high concentration of dark charges, i.e., holes brought about by unintentional p-type doping of MAPbI3. Hence, the total concentration of holes in the perovskite is hardly affected by optical excitation, which manifested as similar decay kinetics. On the other hand, the decay of the photoinduced conductivity in MAPbI3/PCBM is on the time scale of hundreds of picoseconds to several nanoseconds, due to electron injection into PCBM and electron-hole recombination at the interface occurring at similar rates. These results highlight the importance of understanding the role of dark carriers in deconvoluting the complex photophysical processes in these materials. Moreover, optimizing the preparation processes wherein undesired doping is minimized could prompt the use of organic molecules as a more viable electrode substitute for perovskite solar cell devices.

Femtosecond Charge‐Injection Dynamics at Hybrid Perovskite Interfaces

“…Figure a shows differential transmission (Δ T / T ) spectra measured on the mAl 2 O 3 substrate (dynamics at selected probe wavelengths are reported in Figure b). In the visible range, in agreement with reports in the literature, the spectra are dominated by a positive band with a maximum at λ ≈760 nm, with a tail extending towards λ =710 nm. The band at λ =760 nm is assigned to photobleaching (PB) due to state filling.…”

“…Notably, the absorption of the oxidized species provides spectral signatures of the charged HTM, which is crucial for its identification in the transient spectra, particularly for the IR region. With the aim of understanding the interface dynamics, we performed femtosecond transient absorption (TA) spectroscopy extended down to the near‐IR region; a critical spectral window that is almost unexplored in perovskites so far . To identify the main perovskite spectral signatures and differences that might arise due to electron/hole injection, we first compared the behavior of the perovskite deposited on the injecting mTiO 2 and on the noninjecting mesoporous Al 2 O 3 (mAl 2 O 3 ) substrates (Figure ).…”

Enhancing photoluminescence yields in lead halide perovskites by photon recycling and light out-coupling

“…We attribute this monomolecular non-radiative recombination to a trap-assisted Shockley-Read-Hall recombination, which has been reported before and studied in detail253637. The processes of carrier trapping, de-trapping and subsequent recombination can be described in more detail, but this is beyond the scope of this work.…”

Direct Observation of Ultrafast Hole Injection from Lead Halide Perovskite by Differential Transient Transmission Spectroscopy

“…The time scale of the charge injection from the perovskite to the HTM layer remain controversial despite the extensive previous studies [5][6][7][8][9][10][11][12][13][14], however. The time constant of the hole injection from CH3NH3PbI 3 (MAPbI 3 ) to spiro-OMeTAD in the previous reports, for example, scattered widely from <80 fs [7] to 0.7 ps [8,9] to 8 ps [10]. The hole injection to NiO x was reported to be complete on sub-picosecond time scale [11], whereas those * ishioka.kunie@nims.go.jp to poly(triarylamine) (PTAA), poly(3-hexylthiophee-2,5-diyl (P3HT), and poly [2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta [2,1-b;3,4-b'] dithiophene)-alt-4,7-(2,1,3-benzothiadiazole) (PCPDTBT) were reported to occur on sub-nanosecond time scales [12].…”