Additive‐Morphology Interplay and Loss Channels in “All‐Small‐Molecule” Bulk‐heterojunction (BHJ) Solar Cells with the Nonfullerene Acceptor IDTTBM

Abstract

Achieving efficient bulk-heterojunction (BHJ) solar cells from blends of solution-processable small-molecule (SM) donors and acceptors has proven particularly challenging due to the complexity in obtaining a favorable donor-acceptor morphology. In this report, we examine the BHJ device performance pattern of a set of analogous, well-defined SM donors -DR3TBDTT (DR3), SMPV1, and BTR -used in conjunction with the SM acceptor IDTTBM. Our examinations show that the nonfullerene "All-SM" BHJ solar cells made with DR3 and IDTTBM can achieve power conversion efficiencies (PCEs) of up to ca. 4.5% (avg. 4.0%) when the solution-processing additive 1,8diiodooctane (DIO, 0.8% v/v) is used in the blend solutions. The figures of merit of optimized DR3:IDTTBM solar cells contrast with those of "as-cast" BHJ devices from which only modest PCEs <1% can be achieved. Combining electron energy loss spectrum (EELS) analyses in scanning transmission electron microscopy (STEM) mode, carrier transport measurements via "metalinsulator-semiconductor carrier extraction" (MIS-CELIV) methods, and systematic recombination This article is protected by copyright. All rights reserved. 3 examinations by light-dependence and transient photocurrent (TPC) analyses, we show that DIO plays a determining role -establishing a favorable lengthscale for the phase-separated SM donoracceptor network and, in turn, improving the balance in hole/electron mobilities and the carrier collection efficiencies overall.

Deciphering the Role of Fluorination: Morphological Manipulation Prompts Charge Separation and Reduces Carrier Recombination in All‐Small‐Molecule Photovoltaics

“…Further insights into the charge recombination dynamics and extraction across BHJ active layers in complete devices were obtained through TPV and TPC measurements. The carrier lifetimes ( τ ) under open‐circuit conditions (Figure c) were extracted from the TPV decay dynamics using monoexponential fits under a 1 sun bias . The IDIC‐4F BHJ device exhibits a τ value of 1.92 μs, obviously longer than that of the IDIC counterpart (1.36 μs), in agreement with the lower extent of recombination analyzed earlier.…”

Use of the Phen‐NaDPO:Sn(SCN)2 Blend as Electron Transport Layer Results to Consistent Efficiency Improvements in Organic and Hybrid Perovskite Solar Cells

“…Additional information on trapping/detrapping process and its effect on the charge transport was gathered using the transient photocurrent technique (TPC) . Here the cell is excited by a square‐shaped light pulse with varying intensity long enough for the current density to reach a steady state.…”

“…The active layer thicknesses were measured with a Tencor surface profilometer. The carrier mobilities were calculated by fitting the diodes' data to the Murgatroyd expression (Equation ) where µ 0 is zero‐field mobility, L is the film thickness, J is the dark current density, V is voltage, ε 0 is vacuum permittivity, ε r is the dielectric constant (taken as 3.3 for the organic layer), and β is the field activation factor.…”

Over 12% Efficiency Nonfullerene All‐Small‐Molecule Organic Solar Cells with Sequentially Evolved Multilength Scale Morphologies

“…For example, Hou and co‐workers have recently demonstrated high J sc over 18 mA cm −2 in NFSM‐OSCs by combining a slightly lower bandgap acceptor, IT‐4F ( E g = 1.52 eV) with a mid‐bandgap donor . However, the photoresponse for all of the high performing NFSM‐OSCs reported so far are below 820 nm, which limits the potential to further increase J sc . Considering that near‐infrared (NIR) nonfullerene acceptors ( E g < 1.4 eV) have been widely used in NFP‐OSCs to achieve high J sc of >23 mA cm −2 , it is rational to apply similar NIR absorbing acceptor/donor to NFSM‐OSCs.…”