Spin‐Optoelectronic Phenomena for a Semitransparent Nonfullerene Photovoltaic System

Abstract

A unique feature of nonfullerene acceptors (NFAs) is their strong photoabsorption capability at longer wavelengths and electrostatic potentials (ESPs), which is expected to increase the photocurrent density (J) for bulk heterojunction (BHJ)‐based semitransparent organic solar cells (ST‐OSCs). Indeed, the interior spin‐optoelectronic phenomena are incredibly rich, and it remains challenging to correlate them with a complete photovoltaic process. Here, a prototypical PTB7‐Th: IEICO‐4F‐based ST‐OSC, with an average visible transmittance (AVT) of ≈26.8%, is fabricated for studying the issue (PTB7‐Th: poly[4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b;4,5‐b′]dithiophene‐2,6‐diyl‐alt‐(4‐(2‐ethylhexyl)‐3‐fluorothieno[3,4‐b]thiophene‐)‐2‐carboxylate‐2‐6‐diyl)]; IEICO‐4F: 2,2′‐((2Z,2′Z)‐(((4,4,9,9‐tetrakis(4‐hexylphenyl)‐4,9‐dihydro‐sindaceno[1,2‐b:5,6‐b′]dithiophene‐2,7‐diyl)bis(4‐((2‐ethylhexyl)oxy)thiophene‐5,2‐diyl))bis(methanylylidene))bis(5,6‐difluoro‐3‐oxo‐2,3‐dihydro‐1H‐indene‐2,1‐diylidene))dimalononitrile). Spin‐dependent electron–hole dissociation and charge transport dynamics are systematically studied in the dark condition, the short‐circuit current density (Jsc) condition, and some intermediate stages by the nondestructive in situ magnetophotocurrent (magneto‐J) technique. Some intriguing mechanisms such as the Coulomb blockade–based bipolaron, the spin‐dependent polaron pair dissociation at charge transfer states (CTSs), and the triplet‐polaron reaction are extensively explored in the study. Despite these, the monochromatic light‐induced polarizability is validated to have a remarkable impact on the magnitude of the open circuit voltage (Voc). This work is completely devoted to the spin‐optoelectronic phenomena of the NFA‐based ST‐OSC in working condition.

Investigating Underlying Mechanisms for Nonfullerene Hybrid Bulk Heterojunctions‐Based Organic Magnetoresistance

“…Previously, a mean value of B hf <2 mT was also found in the PTB7‐Th:IEICO‐4F system. [ 19 ] The reduction of the B hf implies that the ISC and RISC events have less probability to happen for the nonfullerene BHJ systems.…”

“…Previously, a mean value of B hf <2 mT was also found in the PTB7-Th:IEICO-4F system. [19] The reduction of the B hf implies that the ISC and RISC events have less probability to happen for the nonfullerene BHJ systems. Based on our experimental results and the theoretical analyses, the PM6:Y6 organic BHJ system has the smallest Δg and B hf.…”

“…[ 25 ] The method has been adopted for investigating a semitransparent organic solar cell as well. [ 19 ] Despite these, ultrafast laser spectroscopy and magnetic resonant spectroscopy have been applied for the study of the energy loss mechanism. [ 26 ] As a matter of fact, the electronic spin property in the organic NFAs cannot be ignored.…”

“…Different from the electronic charge, the electronic spin has more degrees of freedom to be manipulated by external stimuli recognized as potential candidates in applications of highperformance, semitransparent, and flexible organic BHJ solar cells. [18][19][20][21] The aim of using the BHJ, in contrast to the single molecular junction and the planar molecular heterojunction, is to obtain charge transfer states (CTS). [22,23] Such hybrid interfacial states (HIS) stem from an interpenetration of a molecular donor (D) and acceptor (A), which is merit for efficient dissociation of photogenerated excitons.…”

Insights into Magneto-Photocurrent and Coherent Spin Mixing for Binary and Ternary Nonfullerene Bulk Heterojunction Organic Solar Cells

“…Nonfullerene acceptor (NFA)-based organic bulk heterojunction (BHJ) solar cells have boosted the photovoltaic power conversion efficiencies (PCEs) to a completely new height. − They are synthesized to be practically useful for future highly efficient, large-scale, semitransparent, and flexible organic solar cells (OSCs). − In competition to the historically well-established fullerene system, the NFAs contain desirable optoelectronic characteristics in terms of feasibly tailored molecular structures, extensive photo-absorption strengths at near infrared regions, and balanced charge-carrier transports. , It has been demonstrated that the dissociation of photogenerated species is firmly linked with the electronic spin property. ,− As a matter of fact, magnitudes of short-circuit current densities ( J sc ) are spin-dependent . In addition, the energy loss due to the polaron back transfer (PBT) from interfacial charge-transfer states (CTSs) to triplet exciton (TE) states is known to be spin-related .…”