Charge pumping in solar cell structure

Abstract

Modern understanding of the material science of semiconductor silicon allowed the authors to propose a new concept of the so-called “charge pumping” in the structures of photovoltaic converters or solar cells. This paper presents theoretical estimates of the rate of separation and collection of light-generated charge carriers in the structures of conventional silicon solar cells and charge-pumped solar cells. Relatively cheaper so-called “solar silicon” of p-type conductivity is typically used in the industrial production of solar cells. This type of silicon is particularly prone to the formation of thermodonor centers. Partial or, at higher temperatures (about 400 °C), even complete overcompensation of the hole type of conductivity in the base region may occur as a result of prolonged heating. This paper presents an original model describing the local formation of n+ regions in the solar cell structure by the so-called “local photon annealing”. These regions were named “charge pumps”. Experimental data on the formation of n+ regions as a result of Li diffusion are reported as an experimental confirmation of the theoretical estimations made in this work. Comparative volt-ampere characteristics of experimental charge-pumped photovoltaic converters and conventional solar cells are presented, showing an up to 30% increase in the short-circuit current Js.c for the experimental structures under standard illumination (AM1.5). The proposed technological aspects of charge-pumped photovoltaic converter fabrication deliver a cheap process and can be implemented in the industrial production of solar cells with little effort.