Origin of Reduced Open-Circuit Voltage in Highly Efficient Small-Molecule-Based Solar Cells upon Solvent Vapor Annealing

Abstract

In this study, we demonstrate that remarkably reduced open-circuit voltage in highly efficient organic solar cells (OSCs) from a blend of phenyl-C-butyric acid methyl ester and a recently developed conjugated small molecule (DPPEZnP-THD) upon solvent vapor annealing (SVA) is due to two independent sources: increased radiative recombination and increased nonradiative recombination. Through the measurements of electroluminescence due to the emission of the charge-transfer state and photovoltaic external quantum efficiency measurement, we can quantify that the open-circuit voltage losses in a device with SVA due to the radiative recombination and nonradiative recombination are 0.23 and 0.31 V, respectively, which are 0.04 and 0.07 V higher than those of the as-cast device. Despite of the reduced open-circuit voltage, the device with SVA exhibited enhanced dissociation of charge-transfer excitons, leading to an improved short-circuit current density and a remarkable power conversion efficiency (PCE) of 9.41%, one of the best for solution-processed OSCs based on small-molecule donor materials. Our study also clearly shows that removing the nonradiative recombination pathways and/or suppressing energetic disorder in the active layer would result in more long-lived charge carriers and enhanced open-circuit voltage, which are prerequisites for further improving the PCE.

Understanding the Effect of the Third Component PC71BM on Nanoscale Morphology and Photovoltaic Properties of Ternary Organic Solar Cells

“…When treated with 0.5% 1‐chloronaphthalene (CN) and thermal annealing (TA) at 110 °C for 10 min, the inverted binary device (PTQ10:Y6) displayed a satisfactory PCE of 15.03%, with a relatively high V oc of 0.851 V. With the addition of PC 71 BM as the third component to construct ternary OSCs, higher performance of 16.07% was obtained with enhanced short‐circuit current density ( J sc ) and better fill factor (FF). In addition, the morphology of the active layer of the OSCs was studied by grazing‐incidence wide‐angle X‐ray scattering (GIWAXS), photo‐induced force microscopy (PiFM), and transmission electron microscopy (TEM) …”

Significantly Enhanced Molecular Stacking in Ternary Bulk Heterojunctions Enabled by an Appropriate Side Group on Donor Polymer

“…On the contrary, the V OC of P2 ternary system hardly changes with the content of NCBDT‐4Cl, which could be correlated with the cascade structure model (see Tables S1 and S2 in the Supporting Information). [ 21,53–56 ] Obviously, the P1 and P2 binary PSCs exhibit comparable device performance and P2:LA1 even shows a higher PCE than P1:LA1, which indicates that biphenyl side group could be a good candidate for constructing high performance binary PSC than phenyl side group. However, distinct device performance of P1 and P2 based ternary PSCs were observed, which could be attributed to the disturbed micromorphology induced by the extended entanglement of polymer chains.…”

Impact of Alkyl Side Chains on Optoelectronic and Photovoltaic Properties of Novel Benzodithiophenedione‐Based Conjugated Polymers

“…In particular, we varied weight ratio of polymer/PCBM in the blends, active layer thickness (translated to speed of films deposition), processing additives and additive concentration, annealing temperatures, etc. Finally, a solvent vapor annealing technique (SVA) was applied to control the morphology of the blend films . Detailed processing conditions and corresponding photovoltaic parameters are summarized in Tables S1–S12, Supporting Information.…”