TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Device: The device comprises: a first hole-collecting electrode optionally coated onto a transparent substrate; optional layer(s) adjacent to the first electrode, such as an electron-blocking, exciton-blocking, or hole-transporting layer; a layer comprising a mixture of an electron acceptor material and an organic non-polymeric electron donor (preferably a layer comprising a mixture of an organic non-polymeric electron acceptor material and an electron donor), where the electron donor comprises the compound (Ia); optional layer(s) such as hole-blocking, exciton-blocking, or electron-transporting layers; and a second electron-collecting electrode.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Compounds: The compound (I) is selected from 15 compounds as given in the specification e.g. compounds of formulae (Ia), (Ib), (Ic), (Id) and (Ie) (preferably compounds of formula (Ia'), (Ic') and (Id')).X2, X3, X4, Y2, Y3 and Y4=-C(W')-, or CH;n=0-5;A1 and B1=6-10C, 6-20C or 6-30C optionally substituted (hetero)aryl (preferably A1 is thiophenyl, pyrrolyl, furanyl, phenyl, phospholyl benzodithiophenyl, spirofluorenyl, spirothiophenyl, bithiophenyl, terthiophenyl, thienothiophenyl, dithienothiophenyl, benzothiophenyl, isobenzothiophenyl, benzodithiophenyl, cyclopentadithiophenyl, silacyclopentadienyl, silacyclopentadienebithiophenyl, indolyl, benzenyl, naphthalenyl, anthracenyl, perylenyl, indenyl, fluorenyl, pyrenyl, azulenyl, pyridinyl, oxazolyl, thiazolyl, thiazinyl, pyrimidinyl, pyrazinyl, imidazolyl, benzoxazolyl, benzoxadiazolyl, benzothiazolyl, benzimidazolyl, benzofuranyl, isobenzofuranyl, thiadiazolyl, dithienopyrrolyl, dithienophospholyl (all optionally substituted), carbazole 9,9-RR'-9H-fluorenyl, 9-R-9H-carbazolyl, 3,3'-RR'silylenyl-2,2'-bithiophenyl, or 3,3'RR'-cyclopenta(2,1-b:3,4-b')-dithiophenyl; and B1 is thiophenyl, pyrrolyl, furanyl, phenyl, phospholyl, benzodithiophenyl, spirofluorenyl, spirothiophenyl, bithiophenyl, terthiophenyl, thienothiophenyl, dithienothiophenyl, benzothiophenyl, isobenzothiophenyl, benzodithiophenyl, cyclopentadithiophenyl, silacyclopentadienyl, silacyclopentadienebithiophenyl, indolyl, benzenyl, naphthalenyl, anthracenyl, perylenyl, indenyl, fluorenyl, pyrenyl, azulenyl, pyridinyl, oxazolyl, thiazolyl, thiazinyl, pyrimidinyl, pyrazinyl, imidazolyl, benzoxazolyl, benzoxadiazolyl, benzothiazolyl, benzimidazolyl, benzofuranyl, isobenzofuranyl, thiadiazolyl, perfluorylbenzenyl, or carbazolyl (all optionally substituted));R and R'=1-30C alkyl, or 6-30C aryl;B2=6-10C, 6-20C or 6-30C optionally substituted (hetero)aryl, H, F, or 1-16C alkyl (preferably B2 is absent, H, F, 1-16C alkyl, or optionally substituted 6-30C ((hetero)aryl);H1=A1, -B1a-B2a, -A1-B1a-B2a, or group of formula (i);B1a=optionally substituted (hetero)aryl;B2a=H, F, 1-16C alkyl, or optionally substituted (hetero)aryl;K1=optionally substituted (hetero)aryl such 6-10C, 6-20C or 6-30C optionally substituted (hetero)aryl (preferably optionally substituted 6-30C (hetero)aryl);E1=absent, or optionally substituted (hetero)aryl;D1=optionally substituted (hetero)aryl (preferably optionally substituted 6-30C (hetero)aryl);D2=absent, H, F, 1-16C alkyl, or optionally substituted (hetero)aryl (preferably absent, H, F, 1-16C alkyl, or optionally substituted 6-30C ((hetero)aryl);core=2,2',7,7'-yl-9,9'-spirobi(fluorene), 3,3',7,7'-yl-5,5'-spirobi(dibenzo(b,d)silole), 2,2',6,6'-yl-4,4''-spirobi(cyclopenta(1,2-b:5,4-b')dithiophene), or 2,2',6,6'-yl-4,4'-spirobi(silolo(3,2-b:4,5-b')dithiophene);F1 and G1=optionally substituted (hetero)aryl (preferably optionally substituted 6-30C (hetero)aryl);G2=absent, H, F, 1-16C alkyl, or optionally substituted (hetero)aryl (preferably absent, H, F, 1-16C alkyl, or optionally substituted 6-30C (hetero)aryl);R4=6-30C aryl (optionally substituted with greater than or equal to 1 1-16C alkyl);DONOR=group selected from 25 groups as given in the specification e.g. groupe of formulae (ii) and (iii);R11=1-16C alkyl.Provided that:(1) when X2 is CH then Y2 is -C(W')-;(2) when X2 is -C(W')- then Y2 is CH;(3) when X3 is CH then Y3 is -C(W')-;(4) when X3 is -C(W')- then Y3 is CH;(5) when X4 is CH then Y4 is -C(W')-;(6) when X4 is -C(W')- then Y4 is CH; and(7) when only one valence of the DONOR unit is required to bond to the remainder of the molecule, the other valence of the DONOR is terminated by H or 1-20C alkyl. SPECIFIC COMPOUNDS - Use of 46 compounds i.e. 7,7'-(4,4-bis(2-ethylhexyl)-4H-silolo(3,2-b:4,5-b)dithiophene-2,6-diyl)bis(6-fluoro-4-(5'-hexyl-(2,2'-bithiophen)-5-yl)benzo(c)(1,2,5)thiadiazole) of formula (I'); and compounds of formulae (I'a), (I'b), (I'c) and (I'd), is disclosed as the compound (A).