Thermal Activation of PEDOT:PSS/PM6:Y7 Based Films Leads to Unprecedent High Short‐Circuit Current Density in Nonfullerene Organic Photovoltaics

Abstract

Finding an effective approach to suppress trap formation is a potential route for enhancing the performance of nonfullerene organic photovoltaic (NF‐OPVs) devices. Here, an extraordinary short‐circuit current density (JSC) value of 32.65 mA cm‐2 is achieved, higher than the state‐of‐the art NF‐OPVs reported, reaching a high power conversion efficiency (PCE) of 17.92%. This remarkable enhancement is exhibited through the fine‐tuning of PEDOT:PSS/PM6:Y7 films and interface morphologies via applying the prethermal treatment approach (Pre‐TT) to the devices, which exhibit JSC and PCE enhancement of 21% and 8%, respectively, compared to the pristine devices. Accordingly, the dependence of the JSC upon the Pre‐TT approach through a range of morphological, optical, electrical, and advanced transient measurements is investigated. The Pre‐TT‐based films are found to possess optimal smooth blend morphology with better dispersity owing to reduced domain size. Moreover, the measurements show that the optimized treated devices present higher exciton dissociation probabilities and generation rate of the free charge carriers, showing an ideal balanced electron/hole mobility that reveals the JSC and PCE enhancement. Hence, Pre‐TT approach provides a facile passivation strategy that reduces the trap state density of the blend film, improves interface charge transfer, allows balanced electron/hole mobility, and thus promotes device performance.

Antimony-bismuth alloying: the key to a major boost in the efficiency of lead-free perovskite-inspired indoor photovoltaics

“…Figure 7b. This confirms that the Sb alloying in the CABI devices suppresses the nonradiative, trap-assisted recombination pathways, which may warrant an improved device performance through efficient charge transport and collection 25. This behavior of CABI-Sb devices agrees with their lower EU values along with superior JSC and EQE values compared to the case of pristine CABI devices.…”

“…Such a favorable trap energy distribution may mitigate undesirable carrier recombination through the trap states in CABI-Sb, in turn leading to superior performance of CABI-Sb devices. 25,43 The higher internal quantum efficiency (IQE) (Figure S15) of the CABI-Sb cell with respect to CABI reference suggests that a larger portion of the absorbed photons are converted into free carriers, as confirmed by the reduced self-trapping demonstrated by the TA and PL characterization. The free carriers are then successfully collected at the corresponding electrodes in agreement with the superior EQE response of CABI-Sb devices.…”

“…However, as the scattering effects in the absorption measurements cannot be ignored, such a variation in the sub-band gap absorbance for CABI and CABI-Sb samples will be verified with the analysis of the external quantum efficiency (EQE) spectra of the corresponding photovoltaic devices. 25 The XRD and absorption studies overall suggest that CABI-Sb samples retain the crystal structure of CABI and exhibit the direct band gap nature only when the Bi:Sb precursor ratio is ≥ 90:10. Hence, to investigate the hypothesized beneficial effect of Sb co-alloying we focused our characterization on films with a high Bi:Sb precursor stoichiometric ratio.…”

“…By analyzing the region where the EQE decreases exponentially with decreasing energy (i.e., the sub-band gap region), we can also obtain insights into the density of sub-band gap state distribution (i.e., localized exponentialtail states) 15 . The Urbach energy (EU) 25,42 can be estimated from the following correlation:…”

“…This behavior of CABI-Sb devices agrees with their lower EU values along with superior JSC and EQE values compared to the case of pristine CABI devices. Furthermore, the exponential factor (α) from the power law dependence of JSC on the WLED light intensity (I) (i.e., JSC ∝ I α ) under short-circuit conditions deals with the extent of defect-assisted recombination and the ability of the electrodes of the photovoltaic device to extract the photogenerated charge carriers 5,25. The value of α ≈ 1 (extracted from the log-log plot of JSC vs.…”