Single crystalline silicon solar cells with rib structure

Shuhei Yoshiba,Makoto Konagai,Yukimi Ichikawa,Yusuke Abe,Masakazu Hirai

doi:10.1063/1.4976721

Abstract

To improve the conversion efficiency of Si solar cells, we have developed a thin Si wafer-based solar cell that uses a rib structure. The open-circuit voltage of a solar cell is known to increase with deceasing wafer thickness if the cell is adequately passivated. However, it is not easy to handle very thin wafers because they are brittle and are subject to warpage. We fabricated a lattice-shaped rib structure on the rear side of a thin Si wafer to improve the wafer’s strength. A silicon nitride film was deposited on the Si wafer surface and patterned to form a mask to fabricate the lattice-shaped rib, and the wafer was then etched using KOH to reduce the thickness of the active area, except for the rib region. Using this structure in a Si heterojunction cell, we demonstrated that a high open-circuit voltage (VOC) could be obtained by thinning the wafer without sacrificing its strength. A wafer with thickness of 30 μm was prepared easily using this structure. We then fabricated Si heterojunction solar cells using these rib wafers, and measured their implied VOC as a function of wafer thickness. The measured values were compared with device simulation results, and we found that the measured VOC agrees well with the simulated results. To optimize the rib and cell design, we also performed device simulations using various wafer thicknesses and rib dimensions.

Highlights

The energy conversion efficiency of single crystalline silicon solar cells has improved steadily over the last three decades and recently reached 26%.1. To achieve such high efficiency, several technologies, including heterojunctions,[2] interdigitated back contacts, and optical confinement structures, have been developed. In addition to these technologies, the wafer thickness remains an important factor for increased efficiency
A large thin area remains inside the rib, and this area is easy to break during the fabrication process
If the wafer thickness is smaller than that value, the frequency with which wafers crack during the fabrication process rises dramatically

Summary

Introduction

The energy conversion efficiency of single crystalline silicon solar cells has improved steadily over the last three decades and recently reached 26%.1 To achieve such high efficiency, several technologies, including heterojunctions,[2] interdigitated back contacts, and optical confinement structures, have been developed. We describe the process used to fabricate these solar cells with rib structures and present the fundamental photovoltaic characteristics of the devices, including the results of device simulations.

Results

Conclusion