Selective contacts and fill factor limitations in heterojunction solar cells

Abstract

Crystalline silicon-based heterojunction (HJ) solar cells are becoming the best choice for manufacturing companies, because of the low temperature processes useful for very thin silicon wafers and the possibility to easily achieve cells efficiencies higher than 22% on n-type silicon wafers. However, the maximum cell efficiency is still limited by the typical Fill Factor (FF) value of 82%. This issue is due to several factors, some of which are sometimes underestimated, like the base contact. Indeed, a potential mismatch between the work functions of the transparent conductive oxide and the base doped layer can give rise to a small barrier against electrons collection, which is not easy to recognize when the cell FF overcomes 80%. Also a low doping efficiency of the p-type amorphous layer at the emitter side can negatively affect the FF. In this case, even if high efficiency cells are produced, their full potential is still unexploited. Thus, both selective contacts of the cell, even if apparently optimized to achieve very good results, can hide problems that limit the final cell FF and efficiency. In a previous work, an experimental method and a model to individuate hidden barriers at the base contact on n-type crystalline silicon-based HJs have been provided. In this paper, that model is applied to experimental data obtained from the characterization of both commercial and laboratory level HJ solar cells. Moreover, an easy method to recognize the presence of a barrier to the charge transport at the emitter side of the cell is illustrated.

A MATLAB/GUI for Photovoltaic Modules Performance Simulations Based on Two-Diode Model

“…It allows performance for STC to be extrapolated to local performance for conditions anywhere in the world. This block could be of interest to researchers with a special interest in analyzing of FF loss depending on the T c for the industrial silicon solar cells [77], limitations of FF in heterojunction PV cells [78], assessment the performances and the energy production under various values of T a and G as well as the correlation between the FF and the weather condition [79]. The Equation ( 15) could be changed to another method that adds other meteorological parameters (i.e., T a , G, wind speed and relative humidity) in order to improve the prediction of FF and η, but would require prior experimental analysis at the PV installation site.…”

Innovative PV Technologies for reducing electricity costs

“…The passivation layer acts as a semipermeable membrane for charge carriers extraction. [78] HJT concept has a certain affinity with the metalinsulator-semiconductor structure (MIS), which is based on quantum tunneling effect through a thin dielectric layer. To take advantage from the high passivation level of HJT structure, it is fundamental to use monocrystalline silicon with high minority-carrier diffusion length, in the millisecond range.…”

“…It is possible to even improve HJT performances by using materials with high work-function (WF) and higher band-gap to create, in correspondence of the electrodes, a higher offset in the conduction band (for electrons) or in the valence band (for holes). [78] Such a band structure can keep away the minority charge carriers from the electrodes allowing only the majority charge carriers to be extracted. Furthermore, since the selective contact and the absorber own different WF, a band bending can be observed in the absorber band structure.…”

SnCl4-Treated Ti3C2Tx MXene Nanosheets for Schottky Junction Solar Cells with Improved Performance

“…g ., low-temperature solution processing, have aroused increasing interest in recent years. , To date, various materials including PEDOT:PSS, − carbon nanotubes (CNTs), − graphene, − and some metal oxides − have been examined to make the Schottky junction/heterojunction with Si wafers. For these devices, the electron/hole transport layers (E/HTLs) that extract and transfer free electrons/holes and meanwhile block the holes/electrons from Si play an indispensable role. − Developing effective and long-term stable E/HTL materials and the device fabrication processes suitable for Si-based Schottky junction/heterojunction solar cells has been a significant effort. − …”