Sequentially Deposited versus Conventional Nonfullerene Organic Solar Cells: Interfacial Trap States, Vertical Stratification, and Exciton Dissociation

Abstract

Bulk-heterojunction (BHJ) non-fullerene organic solar cells prepared from sequentially deposited donor and acceptor layers (sq-BHJ) have recently been promising to be highly efficient, environmentally friendly, and compatible with large area and roll-to-roll fabrication. However, the related photophysics at donor-acceptor interface and the vertical heterogeneity of donor-acceptor distribution, critical for exciton dissociation and device 2 performance, are largely unexplored. Herein, steady-state and time-resolved optical and electrical techniques are employed to characterize the interfacial trap states. Correlating with the luminescent efficiency of interfacial states and its non-radiative recombination, interfacial trap states are characterized to be about 50% more populated in the sq-BHJ devices than the ascast BHJ (c-BHJ), which probably limits the device voltage output. Cross-sectional energydispersive X-ray spectroscopy and ultraviolet photoemission spectroscopy depth profiling directly visualize the donor-acceptor vertical stratification with a precision of 1-2 nm. From the proposed "needle" model, the high exciton dissociation efficiency is rationalized. Our study highlights the promise of sequential deposition to fabricate efficient solar cells, and points towards improving the voltage output and overall device performance via eliminating interfacial trap states.

Reverse dark current in organic photodetectors and the major role of traps as source of noise

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Layer-by-layer fabrication of organic photovoltaic devices: material selection and processing conditions

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Philip‐Leverhulme‐Preise in Chemie 2019

“…Bakulins Gruppe entwickelt zeitauflösende Spektroskopiemethoden und nutzt diese, um das Verhalten molekularer und nanoskaliger Systeme zu untersuchen. In einem Full Paper in Advanced Energy Materials verglichen sie sequenziell abgeschiedene und konventionelle fullerenfreie organische Solarzellen …”