**2. Materials and Methods**

The chemicals used in this study included copper(II) nitrate hemipentahydrate (Cu(NO3)2·2.5 H2O, Alfa Aesar, ACS, 98.0–102.0%, Tewksbury, MA, USA), chromium(III) nitrate nonahydrate (Cr(NO3)3·9 H2O, Alfa Aesar, 98.5%, Tewksbury, MA, USA), magnesium nitrate hydrate (Mg(NO3)2, Avocado Research Chemicals, 99.999%, London, United Kingdom), sodium hydroxide (NaOH, Sigma Aldrich, ≥97.0%, St. Louis, MO, USA), hydrochloric acid (HCl, Fisher Scientific, 37%, Houston, TX, USA), ethanol (EtOH, Fisher Chemical, anhydrous, Houston, TX, USA), 2-methoxyethanol (2-MOE, Acros Organics, 99+%, Houston, TX, USA), acetone (Fisher Chemical, certified ACS, Houston, TX, USA), 2-propanol (IPA, Fisher Chemical, certified ACS plus, Houston, TX, USA), poly(3-hexylthiophene-2,5-diyl) (P3HT, Rieke Metals, LLC, ≥96%, Lincoln, NE, USA), [6:6]-phenyl C61-butyric acid methyl ester (PC61BM, Solenne BV, >99%, Groningen, The Netherlands), [6,6]-phenyl C71-butyric acid methyl ester (PC71BM, Solenne BV, >99%, Groningen, The Netherlands), poly(5-bromo-4-(2-octyldodecyl)-selenophen2-yl)-5,6-difluorobenzothiadiazole-5,5 -bis(trimethylstannyl)-2,2 -bithiophene (PFBT2Se2Th), poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b']dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2 carboxylate-2-6-diyl)] (PTB7-Th, Luminescence Technology Corp., New Taipei City, Taiwan), 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl) dithieno[2,3-d:2 ,3 -d']-s-indaceno[1,2-b:5,6-b']dithiophene (ITIC, 1-Material Inc., Dorval, QC, Canada), chlorobenzene (CB, Sigma-Aldrich, anhydrous, 99.8%, St. Louis, MO, USA), 1,4-dichlorobenzene (DCB, Sigma Aldrich, anhydrous, 99%, St. Louis, MO, USA), diphenyl ether (DPE, Acros Organics, 99%, Houston, TX, USA), chloroform (CF, Sigma-Aldrich, ACS reagent, ≥99.8%, St. Louis, MO, USA), lead(II) iodide (TCI, 99.99%, Portland, OR, USA), methylammonium iodide (Dyesol, Queanbeyan, NSW, Australia), potassium iodide (Alfa Aesar, 99.998%, Tewksbury, MA, USA), dimethylformamide and dimethyl sulfoxide (DMF and DMSO, Sigma Aldrich, anhydrous grade, St. Louis, MO, USA), C60 (Luminescence Technology Corp., >99.5%, New Taipei City, Taiwan), and bathocuproine (BCP) (Sigma Aldrich, sublimed grade, 99.99%, St. Louis, MO, USA). All chemicals were used without further purification. PFBT2Se2Th was prepared according to previous publication, via copolymerization of 4,7-Bis(5-bromo-4-(2-octyldodecyl)selenophen-2-yl)-5,6-difluorobenzothiadiazole (FBT2Se) and 5,5 -bis(trimethylstannyl)-2,2 -bithiophene (2Th) [41].
