Nonlinear Photocurrent Spectroscopy of Layered 2D Perovskite Quantum Wells

Abstract

Two-dimensional coherent photocurrent spectroscopies directly probe the electronic states and processes that are relevant to the performance of a photovoltaic device. In this Letter, we apply two-pulse nonlinear photocurrent spectroscopy to a photovoltaic device based on layered perovskite quantum wells. The method effectively decomposes the photovoltaic response into contributions from separate quantum wells and excited-state species (i.e., either single excitons or biexcitons). Our experiments show that the efficiency of photocurrent generation increases with the size of the quantum well. Overall, the results suggest that energy funneling processes in layered perovskites, which are most prominent in transient absorption spectroscopies, are largely irrelevant to the function of a photovoltaic cell.

Distinguishing Energy- and Charge-Transfer Processes in Layered Perovskite Quantum Wells with Two-Dimensional Action Spectroscopies

“…The spectra are dominated by broad features that are superposed with narrow (∼20 nm widths) exciton resonances on the diagonal of the spectrum near 570, 600, and 640 nm ( n = 2, 3, and 4 quantum wells). The prominence of features with broad line widths is consistent with large contributions from a continuum of excited states. , As discussed in recent work, this aspect of the NLPC spectra differs significantly from transient absorption signals, which are dominated by excitons and have relatively small contributions from continuum states. , Excitons in the n = 4 quantum wells dissociate on the nanosecond time scale as evidenced by the disappearance of the diagonal peak near 640 nm by τ = 2000 ps; the decay of this diagonal peak is not assigned to spontaneous emission because the time scale is relatively short and all signal components are weighted by the production of photocurrent in NLPC spectra. In contrast, the broad components of the signal persist for a length of time far longer the delay range accessible with this instrument.…”

“…To begin, like transient absorption signals, , it is clear by inspection that the exciton resonances are far more prominent in the NLFL spectra. In earlier work, we have suggested that enhanced contributions of continuum states in linear external quantum efficiency and NLPC signals originate in a greater propensity for charge separation . Intense peaks associated with the n = 3 and 4 quantum wells are located on the diagonal of the spectrum near 600 and 640 nm at τ = 1 ps.…”

“…NLPC and NLFL Spectroscopy . Action spectroscopies are conducted using the instrument described in previous work . All experiments are conducted with a 45 fs, 4 mJ Coherent Libra laser system.…”

“…In this work, we use complementary “action spectroscopies” − to distinguish energy- and charge-transfer dynamics in layered perovskite systems. First, nonlinear photocurrent spectroscopy (NLPC) is applied to photovoltaic cells based on layered perovskite films .…”

“…In this work, we use complementary “action spectroscopies” − to distinguish energy- and charge-transfer dynamics in layered perovskite systems. First, nonlinear photocurrent spectroscopy (NLPC) is applied to photovoltaic cells based on layered perovskite films . As shown in Figure , the nonlinear response of a device to a pair of color-tunable laser pulses is measured as a function of the delay between pulses.…”