Evaluation of internal potential distribution and carrier extraction properties of organic solar cells through Kelvin probe and time-of-flight measurements

Abstract

The carrier extraction property of a prototypical small molecule organic solar cell (OSC) composed of copper phthalocyanine (CuPc), C 60 , and bathocuproine (BCP) was studied on the basis of the internal potential distribution and carrier dynamics in the device. The internal potential distribution in the OSC structure at the interfaces and in the bulk region was determined by the Kelvin probe method. Significant potential gradients were found in the CuPc film on indium tin oxide and in the C 60 film on CuPc, consistent with charge transfer through the contacts. Moreover, surface potential of the BCP layer grew linearly with increasing film thickness with a slope of ca. 35 mV/nm (giant surface potential: GSP), which indicated spontaneous orientation polarization in the film. The potential gradient and GSP significantly changed the built-in potential of the device. Current-voltage and modified time-of-flight measurements revealed that the BCP layer worked as an electron injection and extraction layer despite the wide energy gap. These results were discussed based on the contributions of GSP and the gap states in the BCP layer. V

Self-Assembled Electret for Vibration-Based Power Generator

“…The retention time of 10% loss in Alq 3 was 1.4 × 10 3 s. In contrast, the retention time of TPBi was 7.6 × 10 4 s, 54 times longer than that in Alq 3 . These results confirm our expectations and indicate that the V sp stability of TPBi originates from the wide optical bandgap, resulting in weak visible light absorption 34,36,40 . The moderate decrease observed with respect to V sp in TPBi under illumination can be explained by the light absorption at the peak wavelength (372 nm) of the fluorescent lamp in our laboratory, which is a wavelength that agrees with one of the absorption edges of TPBi (see the inset in Fig.…”

“…This occurs because excitons are created by light absorption and are dissociated owing to the internal field in a film, resulting in the compensation of polarisation charge by the photo-generated holes and electrons. However, Tanaka et al reported that GSP decay could not be observed in bathocuproine (BCP) 36 , suggesting the inefficient generation of photocarriers in BCP films relative to Alq 3 owing to the wider optical bandgap of the former (3.5 eV) 37 . This indicates that an SAE with a wide optical bandgap can be used to overcome the problem of light stability.…”

Spontaneous polarization of vapor-deposited 1-butanol films and its dependence on temperature

“…Electronic mail: thanost@chem.uoa.gr phenyl-1H-benzimidazol-2-yl)benzene, 28 2,9-dimethyl-4,7diphenyl-1,10-phenanthroline, 28 1,3-bis[2-(4-tertbutylphenyl) -1,3,4-oxadiazo-5-yl]benzene, 28 tris(7-propyl-8-hydroxyquinolinolato) aluminum(III), 31,32 and bathocuproine. 33 One recent publication 19 appears to provide some convincing explanation regarding water films based on previous simulations 34 and recent data. There has been no theoretical work addressing the creation of polarized films upon vapor condensation at low or high temperatures.…”

“…Incidentally, the question has already been answered to some extent by experiments studying the formation of organic light emitting diodes. [20][21][22][23][24][25][26][27][28][29][30][31][32][33] Polarized films have been deposited at room temperature under vacuum conditions, which were robust enough to retain their voltage in air or allow mechanical manipulations. Heat or visible light was found to eliminate the voltage.…”

Nonequilibrium Theory of the Conversion Efficiency Limit of Solar Cells Including Thermalization and Extraction of Carriers

“…Such time delays would be important in thicker solar cells and appear to be critical in solar cells using nanocrystals, organic solar cells 31,32 (including dye-sensitised 33 ), and perovskite solar cells 34 , which have low carrier mobilities caused by disorders and the Frenkel-like localization 35,36 of excitons. τ out could be measured using specific characterization methods that are suitable for each system, e.g., by optical characterization of the lifetimes of photo-generated carriers under short-circuit conditions and by transient measurement of the photocurrents 37,38 .…”