Quantifying interface states and bulk defects in high‐efficiency solution‐processed small‐molecule solar cells by impedance and capacitance characteristics

Abstract

The AC properties of high-efficiency (η = 8.01% under standard 100 mW/cm 2 AM1.5 illumination) small-molecule bulk heterojunction (SM BHJ) solar cells (p-DTS(FBTTh 2 ) 2 /PC 70 BM) at different DC biases and frequencies of small amplitude (±10 mV) AC signal in the dark at room temperature were investigated in details. We showed the presence of interface states at the heterojunction interface and determined their parameters from the analysis of spectral distributions of real and imaginary components of the measured impedance. The dielectric constant of BHJ ε BHJ = 2.9 was determined from the geometrical capacitance of totally depleted BHJ layer. We explained quantitatively the effect of interface states and series resistance on the measured C-V characteristics of the SM BHJ solar cells at both low and high frequencies. The quantitative value of the density of defect states in the bulk N = 1.05 × 10 16 cm À3 was determined from the high frequency C-V characteristic corrected by the effect of the series resistance.

Defect Dynamics in Proton Irradiated CH3NH3PbI3 Perovskite Solar Cells

“…The value of the built‐in voltage V bi can be estimated by extrapolating the linear parts of the J – V curves to J = 0 . Both devices show almost the same built‐in voltage of V bi = 0.97 V. This indicates that the dose of 10 13 p cm −2 does not change the work functions of the electron and hole collecting electrodes.…”

Causes and Solutions of Recombination in Perovskite Solar Cells

“…V TFL is obtained by fitting the dark J – V curves. The dielectric constant of the perovskite can be obtained from Equation where C g is the geometrical capacitance of the perovskite layer, the permittivity of free space ε 0 = 8.85 × 10 −14 F cm −1 , L is the thickness of the perovskite films, and A is the active area of the device . C g is obtained by fitting the impedance spectra of the corresponding devices.…”

Understanding the open circuit voltage in organic solar cells on the basis of a donor-acceptor abrupt (p-n++) heterojunction

“…Such an analysis supported a theory with a predominant flat band situation in the non-intentionally doped cells as a general phenomenon caused by mesoscale order. However, the capacitance vs. voltage (C-V) characteristics of numerous functional systems indicates that band bending fully extends within the semiconductor with the lower charge carrier concentration (Liu et al, 2008;Guerrero et al, 2013;Dibb et al, 2013;Deledalle et al, 2015;Brus et al, 2015). This indicates that the non-intentional doping concentrations in the semiconductor active layer determine the band bending in the solar cell.…”