Understanding the Composition of Layer‐by‐Layer Deposited Active Layer at Buried Bottom Surface

Abstract

Layer‐by‐layer (LbL) coating is becoming a widely used method to fabricate nonfullerene active layer films for organic solar cells. However, the vertical compositional distribution of the LbL‐coated active layer, particularly at the buried bottom surface, is not clear yet. In common sense, it is believed that the LbL‐coating yields a donor–mixture–acceptor (D–m–A) vertical distribution in the active layer, i.e., a thin polymer donor layer at the bottom surface, a thin acceptor layer at the top surface and a donor‐acceptor mixture in the middle. In this study, it is shown that the LbL active layer vertically is an entire donor:acceptor mixture. A pure layer of polymer donor doesn't exist at the bottom surface. The LbL active layer delivers high performance in both conventional and inverted device structures. A thin polymer layer with different thicknesses (2, 6, 12 nm) is inserted at the bottom surface to study their effects on the device performance. Those inserted layers substantially deteriorate the device's performance. Furthermore, the assumption is further confirmed by X‐ray photoelectron spectroscopy measurement on the exposed “originally buried” surface. This study sheds light on understanding the vertical compositional distribution of active layer via layer‐by‐layer solution processing.

High-Efficiency Ternary Polymer Solar Cells with a Gradient-Blended Structure Fabricated by Sequential Deposition

“…This distribution is beneficial for establishing a more effective exciton collection and charge transport system. In addition, the donor and acceptor completely permeate each other in the vertical direction, and there is no pure donor layer or the thickness of the pure donor phase is less than 10 nm . The formed gradient-blended structure is depicted in Figure .…”

“…In addition, the donor and acceptor completely permeate each other in the vertical direction, and there is no pure donor layer or the thickness of the pure donor phase is less than 10 nm. 27 The formed gradient-blended structure is depicted in Figure 2. We speculate that the existence of a certain amount of a pure donor phase will increase the probability of trap-assisted recombination at the active layer bottom, consequently diminishing the efficiency of device operation.…”

“…The constructed PSCs achieved an impressive efficiency of 19.6%. In addition, the introduction of additives with different boiling points can interact with the donor and acceptor phases and then improve the device’s performance. , Additionally, the fabrication of multicomponent devices facilitates the coordination of multifunctional optimization, such as broadening absorption, reducing energy loss, controlling morphology, and balancing exciton separation and charge transport. − …”

Sequential Deposition Processing to Control Vertical Composition Distribution toward High‐Performance and Stable Inverted Organic Solar Cells

“…[10] Noticeably, some other studies suggest that the SD method realizes a D:A mixture form rather than a D-m-A structure in OSCs. [16] In this work, to clarify the mechanism of the SD method, the D-m-A structure was applied in inverted photovoltaic devices. As mentioned above, a pure donor layer in the bottom will hinder the transport and collection of separated electrons in principle.…”

Bicontinuous donor and acceptor fibril networks enable 19.2% efficiency pseudo‐bulk heterojunction organic solar cells

“…While it is not challenging to realize fibrillation for neat organic components, this situation can be very complicated when binary or ternary components are mixed to construct photoactive layer for OSCs, as their self‐assembly can compete with each other. [ 32,33 ] Although very recent works have demonstrated that the fibrillization of polymer donors or NFAs in mixed films can be enhanced via the co‐crystallization of the conjugated polymers having high compatibility (i.e., D18‐Cl and PM6) [ 25,34 ] or NFAs with similar molecular packing forms (i.e., BTP‐ThMeCl and L8‐BO), [ 35 ] it is still difficult to construct fibrils of donor and acceptor components simultaneously to realize bicontinuous charge transport networks.…”