Advanced silicon solar cell technologies employ multilayer architectures and offer significant potential to improve power conversion efficiency. However, fabrication-induced nonidealities often lead to charge-transport issues and reduced photovoltaic performance. Therefore, a systematic assessment of the device is essential to pinpoint the specific regions of performance loss and to enable targeted optimization. This study applies detailed impedance spectroscopy (IS) with a broadband AC signal in the range of 1 Hz to 1 MHz for silicon heterojunction (SHJ) solar cells; one is defect-dominated charge transfer in a-Si:H layer, another one is hindered charge transport at the p-a-Si:H/ITO hole-selective contact, and an optimized SHJ cell. These effects manifest within a distinct frequency range of the IS response, thereby enabling the identification of the dominant charge-carrier resistive and recombination-loss mechanisms. A deeper analysis of the Nyquist plot, together with frequency-dispersed phase shifts and real and imaginary impedance responses (Z′, Z″), provides clear signatures of the specific location of the performance loss. It is observed that the optimized device has a well-established depletion region and minority-carrier diffusion, with negligible resistive drop across the device. However, in unoptimized devices, additional charge-delay and impedance features appear within a specific frequency range, revealing distinct origins of the performance loss: one associated with the i-a-Si:H layer and the other with the ITO contact. Therefore, IS provides a powerful basis for diagnosing distortions in photocurrent–voltage graphs, degradation pathways, and transport bottlenecks. The frequency-resolved IS can be a critical tool for guiding interface engineering and process optimization of any optoelectronic device.
Sharma et al. (Thu,) studied this question.