Minimizing energy loss is of critical importance in the pursuit of attaining high-performance organic solar cells. Interestingly, reorganization energy plays a crucial role in photoelectric conversion processes. However, the understanding of the relationship between reorganization energy and energy losses has rarely been studied. Here, two acceptors, Qx-1 and Qx-2, were developed. The reorganization energies of these two acceptors during photoelectric conversion processes are substantially smaller than the conventional Y6 acceptor, which is beneficial for improving the exciton lifetime and diffusion length, promoting charge transport, and reducing the energy loss originating from exciton dissociation and non-radiative recombination. So, a high efficiency of 18.2% with high open circuit voltage above 0.93 V in the PM6:Qx-2 blend, accompanies a significantly reduced energy loss of 0.48 eV. This work underlines the importance of the reorganization energy in achieving small energy losses and paves a way to obtain high-performance organic solar cells.
Two dimensional Dion–Jacobson (2D DJ) perovskite
has emerged
as a potential photovoltaic material because of its unique optoelectronic
characteristics. However, due to its low structural flexibility and
high formation energy, extra assistance is needed during crystallization.
Herein, we study the solvent effect on film formation and trap states
of 2D DJ perovskite. It is found that the nucleation process of 2D
DJ perovskite can be retarded by extra coordination, which is proved
by in situ optical spectra. As a benefit, out-of-plane oriented crystallization
and ordered phase distribution are realized. Finally, in 1,5-pentanediammonium
(PeDA) based 2D DJ perovskite solar cells (PSCs), one of the highest
reported open-circuit voltage (V
OC) values
of 1.25 V with state-of-the-art efficiency of 18.41% is obtained due
to greatly shallowed trap states and suppressed nonradiative recombination.
The device also exhibits excellent heat tolerance, which maintains
80% of its initial efficiency after being kept under 85 °C after
3000 h.
Ternary architecture is a promising strategy to further boost the performance of organic solar cells (OSCs). Reducing the bandgap of the active layer materials not only widens the absorption wavelength range and enhances the short‐circuit current (Jsc) of the OSC, but also decreases the open‐circuit voltage (Voc) of the device, leading to a trade‐off situation for the optimization of the material system. Herein, a small‐molecule donor BTID‐2F, featuring a narrower bandgap than that of PM6, is introduced into a PM6:Y6 based system. The redshift in external quantum efficiency indicates the narrower bandgap and better aggregation in the ternary blends than those of binary ones. Interestingly, lower energy disorder and energy loss are also attained for the ternary devices, leading to higher Voc. Furthermore, owing to the suppressed recombination and morphological optimization, a simultaneous enhancement in the Jsc and fill factor boosts the power conversion efficiency (PCE) of ternary OSC to 17.9% compared to 16.62% for the binary device. Likewise, replacing the acceptor with the L8‐BO molecule further improves the ternary PCE to 18.52%. This work indicates an emerging approach for fabricating high‐performance ternary OSCs with a decreased bandgap and increased Voc.
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