Over 10% Efficient CuIn(S,Se)₂ Solar Cells Fabricated From Environmentally Benign Solution in Air

Abstract

A safe and environmentally benign solvent is a requisite for mass production of thin film solar cells via solution methods. Here, a highly industry suitable solvent N‐methyl‐pyrrolidone (NMP) is used for the first time to make a precursor solution with simple compounds of CuCl, InCl3·4H2O and thiourea and fabricate CuIn(S,Se)2 (CISSe) solar cells. A power conversion efficiency of 10.23% has been achieved from the NMP‐based solution when the precursor film was processed in air, which is only 8.55% for film processed in glove box. Characterizations using XRD, Raman, SEM, EDX, and FTIR show air annealing favors decomposition of organic species in the precursor film, which results in high quality absorber materials. Further improvement in device efficiency can be expected by gallium alloying and optimization of device fabrication conditions. The results demonstrate highly efficient thin film solar cells can be fabricated from an industry suitable NMP precursor solution in air, which is promising for simplifying film processing and reducing manufacture cost.

Impact of Absorber Layer Morphology on Photovoltaic Properties in Solution-Processed Chalcopyrite Solar Cells

“…By contrast, metal complexes are formed from metal salts, complexing ligands, and solvents. Thiourea (TU) is generally employed as a complexing agent, and dimethyl sulfoxide (DMSO), N , N -dimethyl­formamide (DMF), and N -methyl-pyrrolidone (NMP) function as ligand and polar aprotic solvent. − Uhl et al dissolved the metal salts of CuCl, InCl 3 , and GaCl 3 in DMSO . The molecular structures of copper–TU–Cl and indium–DMSO–Cl complexes are exhibited in Figure b.…”

“…Instead of using DMSO or DMF, Yu et al adapted an environmentally benign and air-stable NMP solvent. 51 The precursor film was fabricated in atmospheric air, producing a CISSe solar cell with an efficiency of 10.23%.…”

Toward Understanding Chalcopyrite Solar Cells via Advanced Characterization Techniques

“…More recent solution processes have replaced toxic hydrazine as a solvent [ 11,12 ] with benign solvents such as an amine–thiol mixture, [ 13–15 ] alcohol, [ 16–19 ] dimethyl sulfoxide (DMSO), [ 20 ] dimethylformamide (DMF), [ 21–23 ] and N ‐methyl‐pyrrolidone (NMP). [ 24 ] An efficiency of over 15% for solution‐processed Cu(In x Ga 1− x )(Se y S 1− y ) 2 (CIGS) solar cells has also been reached. [ 11–15,17,19,23 ] However, a performance gap still exists between vacuum‐ and solution‐processed CIGS solar cells, and device efficiency requires further improvement.…”

Solution‐Processed Chalcopyrite Solar Cells: the Grain Growth Mechanism and the Effects of Cu/In Mole Ratio

“…[ 27 ] Amine–thiol mixed precursor solution also produces CIGS structured precursor film according to Zhao et al. [ 8 ] From our previously reports, the precursor films fabricated from dimethyl formamide (DMF), [ 29 ] water, [ 30 ] and N ‐methyl‐pyrrolidone (NMP) [ 31 ] molecular solutions all have CIS structure already formed. Different from vacuum methods that require a Cu‐poor composition, we have reported that highly efficient CuIn(S,Se) 2 (CISSe, 14.5%) and Cu(In,Ga)(S,Se) 2 (CIGSSe, 15.2%) solar cells can be fabricated from DMF solution under Cu‐rich condition (Cu/In = 1.05 and Cu/(In+Ga) = 1.05).…”

“…In this work, we have systematically investigated the grain growth of NMP solution processed precursor films with Cu‐poor (Cu/In = 0.9), stoichiometric (Cu/In = 1.0) and Cu‐rich (Cu/In = 1.1) compositions. We choose NMP solution as an example because NMP is an environmentally benign solvent and can be processed in ambient air, [ 31 ] which is important for industrial mass production. Characterizations show that the chalcopyrite structured CIS precursor film takes a direct phase transformation grain growth mechanism to form CISSe absorber, instead of the fusion of secondary phase as that of the vacuum methods.…”