Efficiency loss prevention in monolithically integrated thin film solar cells by improved front contact

Abstract

For thin film solar cells, there is a large gap between the record efficiencies and panel power output. It was found that for a “typical industrial” CIGS cell efficiency of 15.5%, the efficiency drops to 11.7% when it is operating under the circumstances of a monolithically integrated solar panel. Part of this gap is due to limited conductivity and transmittance of the front contact. By application of a metallic grid, the conductivity can be improved by over two order of magnitude at a transmittance loss of only a few percent as was shown experimentally. In addition, modeling was used to quantify the impact of such approach on the power output of monolithically integrated solar panels. This model includes optical and resistive losses, as well as related losses caused by the inhomogeneity of the operating voltage over the surface. Both power output and the different types of losses are mapped out for various cell configurations. Optimization of transparent conductive oxide resistance, cell length, finger width, and finger spacing of grids was performed and led to an efficiency improvement from 11.7% to 13.8% when the front contact is upgraded with a metallic grid consisting of 20 µm wide parallel fingers positioned perpendicular to the interconnect. Further optimization for a wide variety of cell and grid configurations show that for a technically more feasible size of 100 µm wide fingers, the calculated efficiency is still 13.5%. Finally, the power output is mapped out for a large number of configurations as to create an overview and insight in the interdependencies of cell configuration and finger dimensions. Copyright © 2014 John Wiley & Sons, Ltd.

Improved efficiency of Cu(In,Ga)Se2 mini‐module via high‐mobility In2O3:W,H transparent conducting oxide layer

“…Herein, we focused on conventional cell and module structures. In the latter case, however, module structures with metal grids have also been studied to reduce optical and resistive losses and those related to the inhomogeneity of the surface voltage . Even in these structures, a polycrystalline In 2 O 3 ‐based TCO would be preferable to a ZnO‐based TCO.…”

Light management design in ultra-thin chalcopyrite photovoltaic devices by employing optical modelling

“…To compensate for reduced photocurrent, an additional treatment to increase light absorption in the thin absorber needs to be carried out. Different solutions have been reported to increase the short-circuit current density (Jsc), focusing on various aspects, from improving front transparent contacts [15][16][17], using alternative window layers [18,19], implementing anti-reflecting structures [20], inclusion of efficient back reflectors [21,22], introduction of textures and nano-particles to induce light scattering [23][24][25][26][27][28]. A review on light management in thin CIGS is given in [29].…”

Multi-Material Front Contact for 19% Thin Film Solar Cells

“…Recently, however, the full potential of the application of metallic grids with optimized finger and cell dimensions ( i.e. , lower width and larger height) was reported to give a significant boost in thin film solar efficiencies [ 16 ]. Because such approach would add complexity in the manufacturing process, the efficiency gain should be determined and evaluated with respect to manufacturing issues.…”

“…Because such approach would add complexity in the manufacturing process, the efficiency gain should be determined and evaluated with respect to manufacturing issues. Previous study [ 16 , 17 ] was performed on cells with efficiencies of 15.5% and many aspects such as cell layout and absorber material band gap, were not discussed in depth. Moreover, previous designs did not take into account the material interface issue of contact resistance.…”

“…The investigation of contact resistance in solar cells has only briefly been touched [ 18 , 19 ] and its impact on design of monolithically integrated solar panels still needs to be addressed. Moreover, the previous case was limited to low efficiency CIGS or organic PV [ 15 , 16 ] and the case for high efficiency thin film solar cells, spanning a wide range of band gaps should be investigated. In short, there is a lack of knowledge of the impact of the cell layout and specific metal-TCO interaction (e.g., contact resistance) on the preferred grid design and the expected efficiency benefit.…”