Barrierless Free Charge Generation in the High‐Performance PM6:Y6 Bulk Heterojunction Non‐Fullerene Solar Cell

Abstract

Organic solar cells are currently experiencing a second golden age thanks to the development of novel non‐fullerene acceptors (NFAs). Surprisingly, some of these blends exhibit high efficiencies despite a low energy offset at the heterojunction. Herein, free charge generation in the high‐performance blend of the donor polymer PM6 with the NFA Y6 is thoroughly investigated as a function of internal field, temperature and excitation energy. Results show that photocurrent generation is essentially barrierless with near‐unity efficiency, regardless of excitation energy. Efficient charge separation is maintained over a wide temperature range, down to 100 K, despite the small driving force for charge generation. Studies on a blend with a low concentration of the NFA, measurements of the energetic disorder, and theoretical modeling suggest that CT state dissociation is assisted by the electrostatic interfacial field which for Y6 is large enough to compensate the Coulomb dissociation barrier.

Enhanced and Balanced Charge Transport Boosting Ternary Solar Cells Over 17% Efficiency

“…[11,[25][26][27][28] The PM6:Y6 blend exhibits barrierless free charge generation with low recombination, regardless of excitation energy, rendering it a high-performance binary system. [29] In this work, we incorporated a second donor DRTB-T-C4 into the host PM6:Y6 blend to construct ternary OSCs and obtained a very impressive PCE of 17.13% with a V oc of 0.85 V, a J sc of 24.79 mA cm −2 , and an FF of 0.813. The high PCE is mainly attributed to the enhancement of FF.…”

Exciton and Charge Carrier Dynamics in Highly Crystalline PTQ10:IDIC Organic Solar Cells

“…[48] A strong NFA π-π stacking has been reported to enhance charge transport, but not linked systematically with charge generation. [48] Therefore ultrafast spectroscopic studies have shown that charge carriers are also generated efficiently in NFA-based OSCs, [35][36][37][38][39][40] but a detailed photophysical understanding of NFA OSCs still lags behind the continuing, very promising, advances in their device efficiencies.…”

The Bulk Heterojunction in Organic Photovoltaic, Photodetector, and Photocatalytic Applications

“…Temperature-dependent J-V measurements, in fact, reveal nearly barrierless free-charge formation and efficient charge generation as low as 100 K. Computational studies on PM6:Y6 show that the A-D-A-D-A molecular architecture of Y6 induces a large quadrupolar moment on a molecular scale, and its dimerization in a unit cell create an electrostatic bias potential able to compensate the coulombic interaction of the CT, therefore enabling barrier-free CT state dissociation (Figure 5d,e). [182] Moreover, the calculation of the Urbach energy extracted from FTPS measurements revealed an E U (26.7 meV) near the thermal energy (kT), indicating low energetic disorder in the system. Charge recombination processes are often associated with the blend microstructure, which is generally investigated by grazing-incidence wide-angle X-ray scattering (GIWAXS) measurements.…”

“…Several reports suggest that this blend feature a very high IQE in excess of 95%, which suggests an efficient charge generation and extraction. [182] In fact, a detailed study on these processes using time-delayed collection field and IQE measurements showed negligible losses due to exciton and geminate recombination in a PM6:Y6 blend, the reason of the high FF and J SC in the blend. Contrary to previously reported NFA-based systems, PM6:Y6, together with high FF and J SC , shows an exceptionally high V OC .…”

“…d,e) Reproduced under the terms and conditions of the CC-BY Creative Commons Attribution 4.0 license (https://creativecommons.org/licenses/by/4.0). [182] Copyright 2020, The Authors, published by Wiley-VCH.…”