J.-F. Guillemoles

Hot carrier solar cells: Challenges and recent progress

The limiting efficiency on the conversion efficiency of terrestrial global sunlight is not circa 31%, as commonly assumed, but 74%. To reach the lowest possible costs and hence to attain its intrinsic potential as a major source of future sustainable energy supplies, it would appear photovoltaics has to evolve to devices targeting the latter efficiency rather than the former. The hot carrier solar cell, although presenting substantial device challenges, is arguably the highest efficiency photovoltaic device concept yet suggested and hence worthy of efforts to investigate its practicality. Challenges in the implementation of hot carrier cells are identified and progress in overcoming these are discussed.

Four-fold MQWs absorption enhancement in a 430 nm thick InGaAs/GaAsP MQWs solar cell

We study light management in a 430 nm-thick GaAs p-i-n single junction solar cell with 10 InGaAs/GaAsP multiple quantum wells (MQWs). The epitaxial layer transfer on a gold mirror improves light absorption and increases the quantum efficiency in the MQW region by a factor of 4 through the excitation of Fabry-Perot resonances. We show a good agreement with optical simulation and achieve around 9% efficiency. This promising result can be further improved by anti-reflection layers and additional light-trapping solutions.

Hot carrier solar cell efficiency simulation with carrier extraction through non ideal selective contacts

The hot carrier solar cell is an innovative concept of high efficiency 3rd generation photovoltaic, where thermal losses are reduced by slowing the electron thermalization. Such cells offer maximal potential performance equivalent to an ideal multi-junction cell. Energy selective contacts are necessary to insulate the “hot” carriers in the absorber from the “cold” carriers in the outside world. These contacts allow only electrons with one specific energy to be collected. Here we propose a model of a cell with realistic contacts allowing transmission of electrons within a narrow energy range. The influence of the transmission range of the contact on the cell efficiency and on thermal losses is investigated. We show that, in some specific conditions, the acceptable energy width of the selective contacts can be large and semi-selective contacts allow significant efficiency enhancement.

Interface Defects in CIGS-Based Solar Cells From Coupled Electrical and Chemical Points of View

Chemistry of co-evaporated CIGS surfaces submitted to chemical treatments relevant to fabrication steps were investigated by XPS and admittance spectroscopy. A Se XPS signal specific of the CIGS surfaces was identified. Surface states seen by Admittance and surface chemistry are seen to change significantly during the elaboration steps. Consequences for device elaboration are briefly discussed.