Analysis of CIGS‐based thin film solar cells with graded band gap

Abstract

ZnO/n‐CdS/p‐Cu(In,Ga)Se2 thin film solar cells with graded band gap absorber layer have been modelled. The cells are designed to be fabricated on flexible substrates, so, additional requirements and restrictions to metal contacts and interlayer mechanical and electronic properties should be taken into account. The aim is to calculate parameters of Cu(In,Ga)Se2 (CIGS)‐based thin film solar cells, taking into account the buffer layer effect, zone bending and recombination at grain boundaries and another defects, and to introduce band gap gradient in the absorber layer. The model developed is based on one‐dimensional drift‐diffusion approach using the Poisson's equation and continuity equations for electrons and holes. Modelling for various band gap gradient profiles was performed: positive (from 1.08 up to 1.5 eV), zero (1.21 eV) and inverted (from 1.5 down to 1.08 eV) profiles for CIGS layer, and cells' output parameters have been calculated. The nanostructure effects in solar cells formed on a substrate using porous anodic alumina were considered taking into account processes at grain boundaries and nanoordered back contact. Charge carriers accumulation at the interfaces leads to local effective band gap narrowing at the interfaces reducing the conversion efficiency. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Band gap grading and photovoltaic performance of solution-processed Cu(In,Ga)S2 thin-film solar cells

“…[6][7][8] This band gap change in the absorber film can affect the collection and recombination of photocarriers, suggesting that it is feasible to improve solar cell performance by the introduction of a properly graded band gap in the absorber layer. 9,10 Solar cell efficiency is also related to the lifetime of minority-carriers, 11,12 which is determined by the various radiative and non-radiative decay channels of photo-excited carriers. In this regard, a detailed understanding of the correlation between the optical properties of absorber films and the electrical characteristics of solar cells using these films is crucial for the optimization of solar cells.…”