Non-fullerene organic solar cells based on thienopyrroledione comprising random copolymers; effect of alkyl chains

Two new random copolymers, signed as P1 and P2, were designed and synthesized. 5-(2-ethylhexyl)-4Hthieno[3,4-c]pyrrole-4,6(5H)-dione (TPD) was utilized as electron-accepting moiety whereas selenophenewas utilized as spacer, 4,8-bis[5-(2-ethylhexyl) thiophen-2-yl]-2,6-bis(trimethylstannyl)benzo[1,2-b:4,5-b’](BDT(TiC8)), thiophene and alkylthiophene were utilized as donor moieties. Structural analyses of thepolymers were carried out by attenuated total Reflectance-Fourier-transform infrared spectroscopy(ATR−FTIR). Weight-average and number-average molecular weights (Mw, Mn) of the polymers weredetermined via size exclusion chromatography (SEC). Electrochemical and spectroelectrochemicalmeasurements were performed to investigate optoelectronic properties. The polymers were used asdonor polymers in active layer to fabricate non-fullerene, bulk heterojunction (BHJ) organic solar cells(OSCs). BHJ solar cells' device structure is ITO/PEDOT: PSS/Active Layer/LiF/Al, where active layer consistsof ITIC as acceptor and thienopyrroledione containing donors. Various optimization studies (solventselection, donor: determination of acceptor ratio, active layer’s mass ratio optimizations, determinationof the active layer's thickness, additive selection and thermal annealing) were carried out to obtain thebest performance from the devices. The device based on P1: ITIC (1:1) blend with a thickness of 161 nmgave the best performance with a power conversion efficiency (PCE) of 7.94 %. The highest PCE obtainedfrom P2 based organic solar cell is 1.96 %. P2 exhibited low solubility attributed to the lack of alkyl groupsenhancing polymer solubility, electronic properties, and photovoltaic performances. Our study representsa synthetic approach to exhibit alkyl chains' effect on OSCs' performance based on TPD containing randompolymers and non-fullerene acceptors.Two new random donor-acceptor (D-A) copolymers, signed as P1 and P2, were designed and synthesized. Electrochemical and spectroelectrochemical measurements were performed to investigate absorption, energy levels, electronic and optical band gaps for comparison. The polymers were used as donor polymers in the active layer to fabricate non-fullerene, bulk heterojunction (BHJ) organic photovoltaics (OPVs). Investigations were carried out through the conventional BHJ structure; ITO/PEDOT: PSS/Active Layer/LiF/Al, where active layer consists of 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) as the acceptor and thienopyrroledione containing donors. The device based on P1:ITIC(1:1) blend with a thickness of 161 nm gave the best performance with a power conversion efficiency (PCE) of 7.94%, an open-circuit voltage (VOC) of 0.86 V, a short-current density (JSC) of 18.45 mA cm−2 and a fill factor (FF) of 50.12%. The highest PCE obtained from P2 based organic solar cell is 1.96%. P2 exhibited low solubility attributed to the lack of alkyl groups enhancing polymer solubility, electronic properties, and photovoltaic performances. The research outputs exhibit that introduction of alkyl chains on the polymer backbone can enhance device performance