LEPR study of non-fullerene solar cells on the PBDB-T:IT-M base polymer composites



We present a comparative light-induced EPR (LEPR) study of photoinitiation, relaxation, and recombination of charge carriers initiated by achromatic/white and monochromatic (with a photon energy of 1.34-3.41 eV) light in the PBDB-T-based photovoltaic systems with IT-M counterions. Charge carriers, polarons on polymer chains and respective radical anions excited in a disordered composite matrix first fill spin traps, the number, energy depth and spatial distribution of which are determined by the morphology and crystallinity of bulk heterojunctions. By deconvolution of the effective LEPR spectra, the contributions of immobilized and mobile charge carriers (Fig.1a), as well as their main magnetic resonance parameters, were determined separately at the wide variation of the experimental conditions [1].

The interaction of spins occupying different energy levels in the bandgap of the polymer semiconductor provokes the extremal photon-energy sensitivity of the spin-assisted processes carrying out in the polymer composites. Predominant non-geminate recombination of charge carriers follows multistep trapping-detrapping spin hopping between polymer sites and is strongly governed by the number, energy depth, and spatial distribution of spin traps. It was shown that all processes in composites involving spin are spin-assisted and, therefore, are determined by the main magnetic resonance properties of both the spin charge carriers. The introduction of microadditives of the photoactivator 2,5-diphenyloxazole into the system improves the morphology of the composite due to a more intense π-π-interaction between the components. A further at least double improvement in the functionality of the composite is realized when it is modified with small 2,5-diphenyloxazole molecules (Fig.1b). The interactions between different spin carriers contribute to the growth of the exchange interaction between them and stabilize the number of spin charge carriers, mainly localized in the energy traps of the polymer matrix.



This work was performed with financial support from the Russian Foundation for Basic Research, Grant No. 18-29-20011-mk, according to the State Assignment, No. AAAA-A19-119032690060-9.


[1] Krinichnyi V.I., Yudanova E.I., Denisov N.N., Bogatyrenko V.R. // Synthetic Metals. 2020. V. 267. P. 116462.