Progress in thin film CIGS photovoltaics – Research and development, manufacturing, and applications

Abstract

This review summarizes the current status of Cu(In,Ga)(S,Se) 2 (CIGS) thin film solar cell technology with a focus on recent advancements and emerging concepts intended for higher efficiency and novel applications. The recent developments and trends of research in laboratories and industrial achievements communicated within the last years are reviewed, and the major developments linked to alkali post deposition treatment and composition grading in CIGS, surface passivation, buffer, and transparent contact layers are emphasized. Encouraging results have been achieved for CIGS-based tandem solar cells and for improvement in low light device performance. Challenges of technology transfer of lab's record high efficiency cells to average industrial production are obvious from the reported efficiency values. One section is dedicated to development and opportunities offered by flexible and lightweight CIGS modules.

Voids and compositional inhomogeneities in Cu(In,Ga)Se2 thin films: evolution during growth and impact on solar cell performance

“…Statistics in this sense is still missing. It may still be speculated, that a partial void surface passivation could explain the typically observed superiority [1] of wet buffer layer deposition methods as compared to dry ones in case of multi-stage co-evaporated CIGS.…”

“…Recent improvements in the development of Cu(In,Ga)Se 2 (CIGS) solar cells have mostly focused on the optimization of the charge-selective contacts and on the addition of alkali metals for interface modification and doping [1]. Further increases of the device efficiency might be prevented by the presence of structural defects in the CIGS layer, such as voids and compositional inhomogeneities.…”

Single-crystal Cu(In,Ga)Se2solar cells grown on GaAs substrates

“…[1][2][3][4][5][6][7] CIGS solar cells have recently shown conversion efficiencies exceeding 22 and 19.8% for small-area cells (0.5 or 1.0 cm 2 ) [8][9][10] and submodules (24 cm 2 ), 11) respectively. However, almost all CIGS solar cells are based on polycrystalline CIGS layers deposited on soda lime glass (SLG) substrates by a three-stage method 12) or by the selenization and sulfurization of metal precursors.…”

A highly efficient Cu(In,Ga)(S,Se)2 photocathode without a hetero-materials overlayer for solar-hydrogen production

“…Moreover, CuInSe 2 ’s formation temperature is relatively lower than that of CuInGaSe 2 31 . Since the bandgap increase is directly correlated with increases in Ga and S, the bottom layer should have a bandgap higher than the middle layer 22–24,32 . On the other hand, the layer near surface also has a higher bandgap due to the high content of S, which was achieved by continuing sulfurization even after selenization 33–36 .…”

“…The effects of compositional gradients are well documented in the solar cell field 22–25 . The relative amount of Ga and S determines the CIGSSe’s bandgap energy, which can range from 1.04 eV for pure CuInSe 2 to 2.4 eV for pure CuGaS 2 .…”