Re-Examining Open-Circuit Voltage in Dilute-Donor Organic Photovoltaics
Journal
Journal of Physical Chemistry C
Date Issued
2022
Author(s)
Abstract
Dilute-donor (DD) organic photovoltaic (OPV) devices comprise a low concentration of donor molecules in an acceptor matrix. The open-circuit voltage (Voc) of these devices is commonly higher than their bulk heterojunction (BHJ) counterparts and has been attributed to Schottky barrier heights between the anode and the acceptor matrix or reduced bimolecular recombination due to smaller donor/acceptor interfacial areas. Here, we examine the Voc of a variety of small-molecule and polymer donors, all at 5 wt %, in both fullerene and non-fullerene acceptors by performing photovoltaic (PV) and electroluminescence (EL) measurements on the same devices. We find a substantial Voc variation for different donors in the same acceptor matrix, indicating that DD Voc cannot be adequately explained by the Schottky barrier or interfacial area. Voc values of fullerene DD devices vary linearly with the band gap value as determined from the intercept of PV external quantum efficiency and EL spectra. In contrast, the non-fullerene acceptor (NFA) DD devices show Voc variation with donors despite having the same band gap. These results show that Voc of DD OPVs is predominantly determined by non-radiative voltage loss, similar to BHJ OPVs. NFA-based DD devices show promises for low voltage loss and high charge generation. © 2022 American Chemical Society.
SDGs
Other Subjects
Electroluminescence; Energy gap; Heterojunctions; Molecules; Open circuit voltage; Schottky barrier diodes; Timing circuits; Bulk heterojunction; Donor molecules; Interfacial areas; Low concentrations; matrix; Open-circuit voltages; Organic photovoltaic devices; Organic photovoltaics; Photovoltaics; Voltage loss; Fullerenes
Type
journal article