| dc.description.abstract | This work presents a comprehensive study on establishing a reliable characterization methodology based on the Photoelectromagnetic (PEM) effect in semiconductors. When a semiconductor surface is incident by photons of energy higher than its bandgap, electron-hole pairs are generated on the surface. Due to the concentration gradient, these excess carriers diffuse into the bulk of the semiconductor.
When an external magnetic field is applied perpendicular to the diffusion gradient, the photo-diffused carriers get deflected in the opposite direction. This generates an open circuit voltage and is called the PEM effect. When connected to an external circuit, a PEM short circuit current flows in the circuit, which is directly proportional to the mobility, magnetic field, photon flux, and effective diffusion length of the semiconductor. The PEM short circuit current is proportional to the product of mobility and effective diffusion length, whereas the conventional photocurrent is proportional to the mobility lifetime product. By combining the PEM effect with the photocurrent (PC) measurements, it is possible to extract key transport and recombination parameters such as carrier mobility, diffusion length, surface and bulk recombination velocity.
One of the most compelling aspects of the PEM-PC method is its ability to capture bulk properties without being overshadowed by surface effects, which often complicate results in traditional measurements. The ratio of PC to PEM signal allows a direct measurement of the bulk carrier lifetime and bulk recombination velocity (BRV), which is defined as the 𝐷/𝐿𝑏, where 𝐷 is the diffusion coefficient and 𝐿𝑏 is the bulk diffusion length of the semiconductor. The parameter 𝐷/𝐿𝑏 determines the open-circuit voltage in solar cells. BRV directly estimates the diode dark saturation
current, 𝐽o, which measures the total recombination in a p–n junction solar cell. In thermal equilibrium, the bulk recombination current due to intrinsic defects (i.e.,SRH recombination) is given as
𝐽𝑡βo(bulk)= 𝑒𝑛o 𝐷/𝐿𝑏
where 𝑛o is the minority carrier concentration, and 𝐷/𝐿𝑏 is the BRV. The 𝐽o is directly related to the open-circuit voltage, hence the BRV provides an estimate for the 𝑉oc measured in a practical solar cell.
The combined PEM and PC data also allow the determination of the lower limit to bulk diffusion length, bulk excess carrier lifetime, and carrier mobility. While an accurate lifetime and SRV estimation is possible with the knowledge of mobility or diffusion coefficient, the lower bounds serve as a qualitative limit for what values of lifetime and mobility to be expected.
In this study, we also determine the absolute values of the Diffusion coefficient and carrier mobility of the perovskite absorber layer in an actual solar cell, where the thickness is comparable to or less than the diffusion length. By performing systematic PEM and photocurrent (PC) measurements, we established a solid framework for extracting these transport parameters in low-dimensional semiconductors.
In summary, this work highlights PEM–PC analysis as a powerful diagnostic tool that bridges the gap between material-level characterization and device-level performance, offering new opportunities for rational interface design and optimization of next-generation photovoltaic devices. | en_US |
