NOVELTY - A photocurable composition comprises a cyano group-containing silicon-based photocurable monomer (A) (I), and a photoinitiator (B).    USE - Photocurable composition is used for organic light-emitting element encapsulation composition and encapsulated device e.g. organic light emitting device, lighting device, metal sensor pads, micro-disk lasers, electrochromic device, photochromic device, micro electro-mechanical system, solar cell, integrated circuit, charge-coupled device and light-emitting diode (all claimed).    ADVANTAGE - The photocurable composition has excellent hardenability, and forms organic barrier layer having excellent adhesiveness with respect to inorganic barrier layer.    DETAILED DESCRIPTION - A photocurable composition comprises a cyano group-containing silicon-based photocurable monomer (A) of formula (I), and a photoinitiator (B).    R1,R2=1-10C alkyl, 2-10C heteroalkyl, 6-20C aryl, 7-21C aryl, 1-10C silyl (all optionally substituted), H or group of formula (a), in which at least one of R1 and R2 is group (a);    asterisk=connection portion of element;    R3=1-10C alkyl, 2-10C heterocyclyl, 6-20C aryl, 4-20C heteroaryl, 7-21C aryl, 1-10C silyl (all optionally substituted), H, hydroxy, halo, or -NR'R";    R4=H or 1-5C alkyl;    R',R"=1-10C alkyl, 2-10C heteroalkyl, 4-20C aryl, 6-20C heteroaryl, 7-21C aryl (all optionally substituted), or H;    X1,X2=single bond or oxygen;and    X3,Y1,Y2=1-10C alkyl, 2-10C heteroalkyl, 6-20C aryl, 7-21C aryl, 4-20C heteroaryl, or 3-10C cycloalkylene (all optionally substituted).    An INDEPENDENT CLAIM is included for encapsulated device, which has a substrate (10) and a barrier stack (30) on the substrate. The barrier stack comprises an inorganic barrier layer (31) on the substrate, and an organic barrier layer (32) formed using the photocurable composition on the inorganic barrier layer.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of encapsulated device.    Substrate (10)    Organic light-emitting element (20)    Barrier stack (30)    Inorganic barrier layer (31)    Organic barrier layer (32)