High-Efficiency Nanoparticle Solution-Processed Cu(In,Ga)(S,Se)₂Solar Cells

Abstract

Thin film Cu(In,Ga)(S,Se) 2-based (generally referred to as CIGS) solar cells represent a promising alternative to conventional crystalline silicon solar cells due to their high efficiencies, reduced cost, and better material utilization. In recent years, it has been demonstrated that it is possible to form thin films by annealing nanoparticulate material such that the nanoparticles coalesce to form large grained thin films. In this paper, we present a 13.8% efficient CIGS solar cell derived from printed nanoparticle inks. The approach was successfully extended to fabricate monolithic devices on larger substrates. These results demonstrate that lowcost, nonvacuum printing of CIGS nanoparticles has great potential to achieve high efficiencies and reduce the performance gap with the more traditional vacuum co-evaporation and sputtering techniques. Index Terms-CIGS and CdTe thin film solar cells, nanoparticles, photovoltaic cells, thin film PV modules and manufacturing. I. INTRODUCTION T HE photovoltaic market is currently dominated by silicon wafer-based solar cells [1]. In this type of solar cells, the active layer is made of single-crystal wafers produced by a process that involves fabricating and slicing high-purity, singlecrystal silicon ingots. This process is expensive and although much of the manufacturing and module equipment has become standardized, the production of crystalline silicon solar cells remains cost-intensive and is characterized by relatively poor material utilization. The high cost of crystalline silicon wafers has prompted both industry and academia to investigate alternative Manuscript

Over 6% Efficient Cu(In,Ga)Se2 Solar Cell Screen-Printed from Oxides on Fluorine-Doped Tin Oxide

“…Interestingly, industrially compatible solution-based coating technologies, such as screen-printing, inkjet-printing, spray-coating, doctor-blade-coating, slot-die-coating, or roll-to-roll-processing, represent viable methods for reducing the energy demand of the CIGSe fabrication . Motivated by the recent report of, in part, solution-processed Cu­(In,Ga)­(S,Se) 2 solar cells with 17.17% efficiency, we became interested in developing a facile screen-printing approach to CIGSe solar cells using commercially available copper­(II) oxide (CuO), indium­(III) oxide (In 2 O 3 ), and gallium­(III) oxide (Ga 2 O 3 ) as the key constituent starting materials. We selected the screen-printing process because this deposition method is feasible for large scale production, and is already widely employed in the PV industry for forming busbars with silver paste.…”

Vacuum-Free and Highly Dense Nanoparticle Based Low-Band-Gap CuInSe2 Thin-Films Manufactured by Face-to-Face Annealing with Application of Uniaxial Mechanical Pressure

“…Vacuum-free processing and improving the scalability of absorber fabrication would be very beneficial. CIGS nanoparticles (NPs) have successfully been used recently to achieve dense absorber layers [2,3] and high-efficiency solar cells, with, for example, 13.8% [4] or 15% [5] efficiency. An alcohol-based molecular precursor yielded 14.4% efficiency [6] while using H 2 Se annealing.…”

Uniform Selenization of Crack-Free Films of Cu(In,Ga)Se2 Nanocrystals

“…Since nanocrystals are typically coated with capping ligands and dispersible in a variety of solvents, they can be deposited using solution-based printing schemes . After deposition, the capping ligands tend to limit the electrical conductivity of the nanocrystal layers and must be removed, either by capping ligand exchange or stripping − or by fusing the nanocrystals by heating. ,− These processes have enabled high mobility thin film transistors (TFTs), ,, high efficiency light-emitting diodes (LEDs), − photodetectors, and photovoltaic devices (PVs). ,,,− …”

“…For PVs, a variety of different nanocrystals have been explored, including PbS, CuInSe 2 , , Cu­(In,Ga)­Se 2 (CIGS), ,, CsPbI 3 , , Cu 2 ZnSnS 4 (CZTS), − CdSe, and CdTe. , Ligand exchange strategies have enabled devices with power conversion efficiencies (PCEs) of just over 13%, , and sintered nanocrystal layers processed at high temperature (300–600 °C) have been used to make devices with even higher efficiency (PCE > 16%). − To ensure consistent ligand removal or sintering and limit shunting in the devices, the as-deposited nanocrystal films need to be uniform . Uniformity is difficult to achieve in a single deposition step for relatively thick films (>200 nm) because of the tendency to form cracks and voids as the solvent evaporates from the deposited ink. , Spin coating has been commonly used to make smooth and continuous nanocrystal films, but this method is only suitable for relatively thin layers (<200 nm), and thicker films require multiple deposition steps. ,− Thick films without cracks have been demonstrated using controlled solvent evaporation or layer-by-layer deposition strategies, ,,,− but these methods are too slow to be used for commercial device fabrication .…”

“…6,10−14 These processes have enabled high mobility thin film transistors (TFTs), 5,15,16 high efficiency light-emitting diodes (LEDs), 17−20 photodetectors, 21 and photovoltaic devices (PVs). 3,8,12,22−24 For PVs, a variety of different nanocrystals have been explored, including PbS, 8 CuInSe 2 , 25,26 Cu(In,Ga)Se 2 (CIGS), 11,12,14 CsPbI 3 , 27,28 Cu 2 ZnSnS 4 (CZTS), 29−31 CdSe, 32 and CdTe. 13,33 Ligand exchange strategies have enabled devices with power conversion efficiencies (PCEs) of just over 13%, 8,27 and sintered nanocrystal layers processed at high temperature (300−600 °C) have been used to make devices with even higher efficiency (PCE > 16%).…”