Ultrafast Spectroscopy with Photocurrent Detection: Watching Excitonic Optoelectronic Systems at Work

Abstract

While ultrafast spectroscopy with photocurrent detection was almost unknown before 2012, in the last 3 years, a number of research groups from different fields have independently developed ultrafast electric probe approaches and reported promising pilot studies. Here, we discuss these recent advances and provide our perspective on how photocurrent detection successfully overcomes many limitations of all-optical methods, which makes it a technique of choice when device photophysics is concerned. We also highlight compelling existing problems and research questions and suggest ways for further development, outlining the potential breakthroughs to be expected in the near future using photocurrent ultrafast optical probes.

Probing polaron excitation spectra in organic semiconductors by photoinduced-absorption-detected two-dimensional coherent spectroscopy

“…According to the final population of interest, one can probe the excitation spectral signals in forms of photoluminescence (PL) [6][7][8] or photocurrent (PC) [9][10][11], for example. Indeed, this implementation of 2D coherent spectroscopy has the formidable advantage that it can exploit photocurrent detection as an extraordinarily sensitive population probe [12]. In this contribution, we demonstrate an alternative approach that is complimentary to PL and PC detection schemes, based on quasi-steady-state photoinduced absorption (PIA).…”

Time-resolved quantum transport for optoelectronics

“…However, these advances have raised some fundamental questions about energy and heat [6], which are crucial for thermodynamics and energy conversion at the nanoscale especially in time-dependent regimes [2]. Morevor, few teams around the world develop specific time-resolved techniques to directly address the photo-carrier dynamics [1], and even less the photo-carrier thermodynamics at the nanometer scale.…”

“…Recent experimental trend toward femtosecond multidynamical excitations has triggered an interest for investigating time-dependent regimes in nanostructured semiconductor, molecular or hybrid electronic systems [1]. Molecular electronic devices form indeed a promising alternative to standard electronic devices due to their fast response on ultra-short time scale.…”

Two-dimensional action spectroscopy of excitonic systems: Explicit simulation using a phase-modulation technique

“…In yet another technique, one uses four collinear pulses with well defined phases and detects the excited state populations as incoherent action signals, such as fluorescence or photocurrent. This technique may be called as action signal detected 2D spectroscopy based on phase modulation [15,25,[30][31][32][33][34][35][36]. All the approaches provide equivalent signals for the different pathways in the nonlinear light-matter interactions [32].…”

“…Generation of the coherent signals in a spatially isolated phase matched direction, on the other hand, requires the sample size to be larger than the wavelength of the incident light field [1,6]. On the computational side, the action signals can be easily calculated by following the total relaxation from the associated excited states, and the signals that are relevant for the 2D spectroscopy can be separated from the other linear and nonlinear signals by using the technique of phase modulation, as it is done in the experiments [15,32,34,35,37]. Moreover, unlike in the experiments where only the combined contributions from the different excited states on the action signals can be measured, the simulations can be used to disentangle the contributions from the individual excited states on the action signals.…”