Revealing Morphology Evolution in Highly Efficient Bulk Heterojunction and Pseudo‐Planar Heterojunction Solar Cells by Additives Treatment

Abstract

Additives treatment is as a very effective strategy to optimize bulk heterojunction (BHJ) morphology. However, the inherent working mechanism of this strategy still lacks systematical investigations in non‐fullerene‐acceptors‐based organic solar cells (OSCs). Herein, a series of BHJ and pseudo‐planar heterojunction (PPHJ) OSCs using PM6 and IT‐4F as the electron donor/acceptor pair, are developed to unveil the promoting effect of solvent additive 1, 8‐diiodooctane (DIO) on active layer morphologies and device performance. The study clearly demonstrates that DIO can increase the crystallinity of IT‐4F significantly, while it has less impact on PM6. It is notable that a new efficiency‐determining crystalline balanced factor (CCLpolymer/CCLacceptor) is put forward, indicating that the more balanced CCLpolymer/CCLacceptor results in more balanced charge mobility and much better short‐circuit current densities (Jsc) and fill factors (FF) of OSCs. The PPHJ blend film of PM6/IT‐4F(DIO) exhibits enhanced crystallinity with more balanced CCL and favorable hierarchical distribution morphology, contributing to a champion efficiency of 13.70% with a record Jsc of 20.98 mA cm−2 and a remarkable FF of 75.9%. This work not only reveals the underlying mechanism of DIO caused morphology evolution, but also achieves highly efficient PPHJ OSCs with superior thermal stability by elaborately controlling the morphology of PPHJ film.

Simultaneously Enhanced Efficiency and Operational Stability of Nonfullerene Organic Solar Cells via Solid‐Additive‐Mediated Aggregation Control

“…Among various morphology optimization strategies, the additive strategy has been thriving since the early stage of BHJ OSCs based on fullerene electron acceptors, [ 21–23 ] and are continuously involved in NFA‐based OSCs. [ 24–28 ] Liquid additives such as 1,8‐diiodooctane (DIO), [ 29 ] diphenyl ether (DPE), and 1‐chloronaphthalene (CN) have been demonstrated to enhance the molecular stacking [ 30,31 ] and crystallinity, [ 32 ] form appropriate phase separation, [ 33 ] increase light absorbance, [ 34,35 ] promote charge separation and transport, [ 36–38 ] and finally improve the photovoltaic performance of OSCs. [ 35,39–41 ] However, a common property of these liquid additives is that they have a relatively high boiling point compared to the primary solvent, making them reluctant to evaporate during solution casting, and even harder to escape in the virtually dried active layer.…”

Unprecedented Long‐Term Thermal Stability of 1D/2A Terpolymer‐Based Polymer Solar Cells Processed with Nonhalogenated Solvent

“…We also calculated the ratio of CCL of polymer and IT‐4F (CCL Polymer /CCL IT‐4F ) to use crystalline balanced factor, and values close to 1 were considered ideal. [ 28 ] The IT‐4F exhibits a (100) peak at 0.32 Å −1 in the in‐plane direction and a (010) peak at 1.68 Å −1 in the out‐of‐plane direction. [ 29 ] As shown in Table S1, Supporting Information, the PBTPBD‐50:IT‐4F blended film exhibited a much better crystalline balanced factor of 0.93 compared with other blended films.…”

“…The crystallization of the PM6 copolymer dominates in the blended film due to the significant crystallinity at 0.28 Å −1 in the in‐plane direction. [ 28 ] This unbalanced crystallization of the PM6 copolymer and IT‐4F is the major reason of the poor photovoltaic performance. In addition, the PM6:IT‐4F blended film exhibited a bimodal orientation with a pronounced (100) peak in the out‐of‐plane direction, indicating the occurrence of an aligned lamella packing.…”

Roles and Impacts of Ancillary Materials for Multi‐Component Blend Organic Photovoltaics towards High Efficiency and Stability

“…At the same time, He et al used a DIO solvent additive to investigate the effects of DIO on the crystallization behavior of each donor and acceptor (i. e., the selective solvency) in a PM6: IT-4F blend film. [99] A pseudo-planar heterojunction (PPHJ) structure was introduced to clearly compare the selective effects of DIO on the PM6 : Y6 blend. The morphological evolution of three kinds of PPHJ films was investigated, with the layer configurations being PM6/IT-4F, PM6/IT-4F(DIO), and PM6(DIO)/IT-4F.…”