Optimized Design of Silicon Heterojunction Solar Cells for Field Operating Conditions

TL;DR

This paper analyzes silicon heterojunction solar cells with carbon-doped layers, demonstrating that while carbon increases transparency, it can improve energy harvesting efficiency in real-world conditions despite lower performance at standard test conditions.

Contribution

It introduces the use of a-SiCx(n) layers with varying carbon content in SHJ cells and shows their benefits under different climate conditions, highlighting real-world performance improvements.

Findings

Adding carbon reduces efficiency at STC but improves real-world energy harvesting.

A 0.4 to 0.8% relative gain in efficiency is achieved with optimal carbon content.

Performance differences are smaller in actual outdoor conditions than at STC.

Abstract

Solar modules are currently characterized at standard test conditions (STC), defined at 1000W/m2 and 25 {\deg}C. However, solar modules in actual outdoor operating conditions typically operate at lower illumination and higher temperature than STC, which significantly affects their performance ratio (average harvesting efficiency over efficiency in STC). Silicon heterojunction (SHJ) technology displays both good temperature coefficient and good low-illumination performances, leading to outstanding performance ratios. We investigate here SHJ solar cells that use a-SiCx(n) layer as front doped layer with different carbon contents under different climates conditions. Adding carbon increases transparency but also resistive losses at room temperature (compared with carbon-free layers), leading to a significant decrease in efficiency at STC. We demonstrate that despite this difference at STC, the difference in energy harvesting efficiency is much smaller in all investigated climates. Furthermore, we show that a relative gain of 0.4 to 0.8 percent in harvesting efficiency is possible by adding a certain content of carbon in the front (n) layer, compared with carbon-free cells optimized for STC.