Direct Probing of Photovoltaic Effect Generated in Double-Layer Organic Solar Cell by Electric-Field-Induced Optical Second-Harmonic Generation

Abstract

By using time-resolved electric-field-induced optical second-harmonic generation (EFISHG) measurement, we directly probed photovoltaic effect generated in double-layer (pentacene/C60) organic solar cells (OSCs). The electric field in C60 layer was selectively probed by using incident laser with a wavelength of 1,000 nm. Results showed that excess positive charges Qs=1.5×10-8 C/cm2 accumulated at the pentacene/C60 interface under photoillumination. These charges generated the interfacial voltage Vs=0.16 V and deformed a potential profile in the OSCs. The EFISHG measurement is an effective way for directly catching carrier behavior at the double-layer interface in OSCs in terms of the photovoltaic effect.

Analysis of interface carrier accumulation and relaxation in pentacene/C60 double-layer organic solar cell by impedance spectroscopy and electric-field-induced optical second harmonic generation

“…7 In the time-resolved SHG measurements, we applied an external field to OSCs under both dark and illuminated conditions. During these measurements, separation of excitons provokes at the pentacene/C 60 interface, and excess charge Q s is expected to accumulate at the interface due to the Maxwell-Wagner effect.…”

“…During these measurements, separation of excitons provokes at the pentacene/C 60 interface, and excess charge Q s is expected to accumulate at the interface due to the Maxwell-Wagner effect. 7,8 The EFISHG probes the change of electric field in the C 60 layer, which is generated from the Q s .…”

“…4 was ascribed to the Maxwell-Wagner type interfacial carrier charging at the pentacene/C 60 interface. 7 On the other hand, in the IS measurements, small ac signal is applied to the OSCs during the measurement, and this activates the electrode charging process with a relaxation time s RC ¼ R 0 C t . This is the reason why relaxation B is always observed in Fig.…”

“…In our previous study, we employed the Maxwell-Wagner (MW) model analysis for studying interfacial phenomena in double-layer organic devices, e.g., double-layer organic light-emitting diode (OLED) and showed the potentiality of this analysis based on a dielectrics physics approach. [7][8][9] These results motivated us to apply the MW model to analyze carrier generation and transport processes in OSCs.…”

Analyzing Open-Voltage of Double-Layer Organic Solar Cells Using Optical Electric-Field-Induced Second-Harmonic Generation

“…The EFISHG measurement was found very effective for tracing carrier behaviors in organic devices [8][9][10]. This motivated us to study carrier mechanism in OSCs in terms of photovoltaic effects [11][12][13].…”