Iron Pyrite / a super absorber for PV solar energy

Reducing the materials costs and improving efficiencies for solar cells is an ongoing research area that has global interest. Currently, crystalline silicon cells account for 90% of the PV market. Whilst conversion efficiency levels are considered high, the production costs for crystalline silicon are significantly higher than for thin film materials. However, the current conversion efficiency for thin film PV is significantly less than for crystalline silicon hence reducing some of the cost advantage. There is considerable scope for thin film solar cell development, where improvements in cell efficiency can be made with improved materials and device structures. One improvement that will lead to better conversion efficiency is to increase the photon absorption into the cell, close to the junction. A promising candidate for application as an absorbing layer in a photovoltaic device is iron pyrite (FeS2). The high absorption coefficient of FeS2 is consistent with its high density of states in the conduction band. The relatively small band gap allows for visible and infrared wavelengths to be absorbed, and the combination of direct and indirect band gap transitions contribute to its high absorption coefficient. However, this has not yet been turned into an efficient PV device. Iron pyrite has the potential to become a very important material for very large scale manufacture of thin film PV modules where the elemental constituents are very abundant and combines with the much smaller amounts of absorber material needed (thickness of 100 nm or less) making this a very sustainable and low cost material.This feasibility proposal will investigate the promising MOCVD route to deposit very thin films of FeS2 and introduce these into a novel p-i-n structure, taking advantage of the recent success with the MOCVD CdTe PV devices on the PV Supergen project. This structure will take advantage of the super-absorption characteristics to sandwich a very thin film absorber between n-type CdS and p-type CdTe:As layers. The purpose will be to show that high efficiency PV devices can be made from FeS2 where the photo-generated carriers are collected by drift in the electric field rather than by diffusion, thus reducing carrier loss. As part of the feasibility it is intended to scope future developments by replacing the CdS and CdTe n-type and p-type layers with more sustainable materials.