Efficient inverted PM6:Y6 solar cells with tuned lateral phase separation and vertical composition distribution via bis(5-chlorothiophen-2-yl)alkane additives

•The BCTA additive combines chlorothiophen units and an alkyl chain into one for PSCs.•BCTAs with various methylene numbers (m) tune the lateral phase separation in BHJ.•BCTAs also lead more donor PM6 enrich near the anode in the PM6:Y6 inverted devices.•The devices show a quasi-normal distribution on performance as m increases in BCTAs.•The inverted PSC with BCTA (m = 4) shows a comparable PCE of 15.6% to the one with CN.