Dithienogermole-Based Nonfullerene Acceptors: Roles of the Side-Chains’ Direction and Development of Green-Tinted Efficient Semitransparent Organic Solar Cells

Abstract

Inspired by the encouraging properties of Ge-fused heterocyclic dithienogermole (DTG) in optoelectronic applications, we here report two narrow-bandgap acceptor−donor′−donor− donor′−acceptor (A−D′−D−D′−A)-type isomeric nonfullerene acceptors based on DTG (DTG-IW with inward-facing side chains vs DTG-OW with outward-facing side chains) for use in organic solar cells (OSCs). The introduction of the inward-facing side chains into the backbone results in extremely confined face-on crystallites in the solid state, as verified by grazing-incidence wideangle X-ray scattering measurements. This result is attributed mainly to a better power conversion efficiency (PCE) of 9.16% in the OSC based on a blend of DTG-IW with a narrow-bandgap PTB7-Th donor polymer, as compared with the corresponding DTG-OWbased one. Furthermore, the appealing feature of the blend mixing of the narrow-bandgap donor and acceptor pair is that it enables the construction of a green-tinted efficient semitransparent OSC with a PCE of 6.19% and transmittance of 50.4% in the green wavelength region through incorporation of the recently formulated semitransparent Ag/Sb 2 O 3 /Ag electrode. Overall, in addition to providing useful perspectives into the side-chain engineering of nonfullerene acceptors, this work highlights that OSC based on the A−D′−D−D′−A-type DTG is a promising narrow-bandgap acceptor for further improvement of the performance of semitransparent OSCs.

Optimizing the Charge Carrier and Light Management of Nonfullerene Acceptors for Efficient Organic Solar Cells with Small Nonradiative Energy Losses

“…The increased fluorine substituent in the end group lead BTP‐C9‐IC4F and BTP‐C9‐N4F exhibited highly ordered (11‐1) diffraction peaks in blend film. [ 59–61 ] In out‐of‐plane direction, the (010) peaks belonging to donor and acceptors highly overlapped. In the blend films, the introduction of acceptors significantly enhanced the π – π stacking.…”

Latest Progress on Photoabsorbent Materials for Multifunctional Semitransparent Organic Solar Cells

“…Yang and co‐workers reported two new isomeric NBG‐NFAs based on a germanium (Ge)‐fused heterocyclic dithienogermole central donor and terminal 2F‐DCI units interconnected by a 2‐ethyl hexyl substituted thiophene unit with a different orientation of alkyl chains position, i.e., DTG‐IW (inward facing) and DTG‐IW (outward facing). [ 138 ] Though both of these NFAs had similar E g values of ≈1.3 eV, the GIWAXS study revealed that DTG‐IW contains highly confined “face‐on” crystallites in the solid state, which might be useful for boosting charge separation and transport in the corresponding devices. Optimized ST‐OSCs based on PTB7‐Th:DTG‐IW blends (green‐tinted color) and semitransparent Ag/Sb 2 O 3 /Ag electrodes delivered the best PCE of 6.19% and AT of 50.4% at 500–540 nm.…”

High‐Efficiency Organic Solar Cells Based on a Low‐Cost Fully Non‐Fused Electron Acceptor

“…Grazing‐incidence wide‐angle X‐ray scattering (GIWAXS) measurement is employed to evaluate the molecule stacking and crystallinity in solid thin films. [ 27 ] As shown in Figure a, the neat film of 4T‐1 had a (100) diffraction at q z = 0.33 Å −1 and a lattice fringe diffraction pattern, reflecting its higher crystallinity. The other three acceptors adopted an edge‐on molecular orientation with more intensive (010) and (100) diffractions along in‐plane (IP) and out‐of‐plane (OOP) directions, respectively.…”