Vibronic coherence contributes to photocurrent generation in organic semiconductor heterojunction diodes

Abstract

Charge separation dynamics after the absorption of a photon is a fundamental process relevant both for photosynthetic reaction centers and artificial solar conversion devices. It has been proposed that quantum coherence plays a role in the formation of charge carriers in organic photovoltaics, but experimental proofs have been lacking. Here we report experimental evidence of coherence in the charge separation process in organic donor/acceptor heterojunctions, in the form of low frequency oscillatory signature in the kinetics of the transient absorption and nonlinear two-dimensional photocurrent spectroscopy. The coherence plays a decisive role in the initial~200 femtoseconds as we observe distinct experimental signatures of coherent photocurrent generation. This coherent process breaks the energy barrier limitation for charge formation, thus competing with excitation energy transfer. The physics may inspire the design of new photovoltaic materials with high device performance, which explore the quantum effects in the next-generation optoelectronic applications.

Novel sulphonic acid liquid crystal derivatives: experimental, computational and optoelectrical characterizations

“…The value of the electrical conductance is increased from 1.52 pS to 35.16 nS by increasing the number of carbons from 6 to 10, Table 4, since the electrical conductance depends mainly on the number and mobility of charge carriers. [69][70][71] By increasing the scan step from 0.01 to 1 V, the lm conductance is increased from 27.7 to 36.6 pS. The high resistances and energy band gaps (Section 3.4) imply that the compounds under investigation are dielectrics, with ionic impurities likely causing the materials' conductivity.…”

Spectroscopic Assessment of Charge‐Carrier Mobility in Crystalline Organic Semiconductors

“…However, the former technique does not directly distinguish between the static and the dynamic disorder, whereas the latter currently cannot access LF vibrations. Impulsive techniques, such as femtosecond transient absorption, [32,33] 2D photocurrent, [33] and time-resolved THz spectroscopies, [34] are also available for studying LF vibrations. Owing to femtosecond time resolution, these methods can provide valuable insights into the role of dynamic disorder in formation of mobile charge carriers in semiconductors in real time.…”

Nature of the different emissive states and strong exciton–phonon couplings in quasi-two-dimensional perovskites derived from phase-modulated two-photon micro-photoluminescence spectroscopy

“…In this regard, phase modulation in nonlinear spectroscopic techniques can provide valuable information about the different types of PL recombination mechanisms and particularly the PL contributions from different electronic states in semiconductor material and other photo-active systems. [31][32][33] These techniques have enabled measurements of extremely small nonlinear signals that are completely covered by background noise. One of the advantages of these techniques is that the effects of ultrafast nonlinear interactions are imprinted on 'action signals' such as fluorescence and photocurrent, which can be phasesynchronously detected.…”