TECHNOLOGY FOCUS - IMAGING AND COMMUNICATION - Preferred Components: The carrier transport layer is a hole transport layer.    TECHNOLOGY FOCUS - POLYMERS - Preparation: No general method for the preparation of the compound (I) is given in the specification. Preferred Compound: In the polymer (I), the repeating unit is 1-(4-(3-(4-((4-butylphenyl)(phenyl)amino)phenyl)-9H-carbazol-9-yl)butyl)-1,2,3,4-tetrahydropyrimidine-2,4-dione; 9-(4-(3-(4-((4-butylphenyl)(phenyl)amino)phenyl)-9H-carbazol-9-yl)butyl)-9H-purin-6-amine; 1-(4-(3-(4-((4-butylphenyl)(phenyl)amino)phenyl)-9H-carbazol-9-yl)butyl)-5-methyl-1,2,3,4-tetrahydropyrimidine-2,4-dione; 4-amino-1-(4-(3-(4-((4-butylphenyl)(phenyl)amino)phenyl)-9H-carbazol-9-yl)butyl)-1,2-dihydropyrimidin-2-one; or 2-amino-9-(4-(3-(4-((4-butylphenyl)(phenyl)amino)phenyl)-9H-carbazol-9-yl)butyl)-6,9-dihydro-1H-purin-6-one. Preferred Definitions:    A'=triphenylamine optionally substituted by butyl;    B'=carbazole optionally substituted by butyl;    C'=an amide-containing group, a carboxyl-containing group, a hydroxyl-containing group, an amino-containing group, a halogen-containing group, and/or T1;    T1=a base-containing group selected from one of adenine, thymine, cytosine, guanine and/or uracil (preferably adenine or uracil).    EXAMPLE - To a mixture of 0.186 g 4-adeninebutyl-9(3,6-dibromocarbazole), 0.2 g 4-butyl-N,N-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolane-4-phenyl)-aniline, and 0.041 g freshly prepared Pd(0)(PPh3)4, was added a deoxygenated mixture of 10 ml tetrahydrofuran (THF), 6 ml dimethylformamide (DMF) and 10 ml aqueous 2M K2CO3. The mixture was vigorously stirred at 85-90 degrees C for 48-72 hours. After the solution was cooled, the whole mixture was poured slowly into a cold mixture of methanol/deionized water (3/1 in volume). The polymer was collected by filtration and washed with methanol. The solid was then washed for 24 hours in a Soxhlet apparatus using acetone to remove oligomers and catalyst residues. Purifying 9-(4-(3-(4-((4-butylphenyl)(phenyl)amino)phenyl)-9H-carbazol-9-yl)butyl)-9H-purin-6-amine (PTC-A) by redissolving in DMF and then precipitated from cold methanol prior to drying at room temperature under high vacuum. The obtained PTC-A compound had number average molecular weight (Mn) of 5000, weigh average molecular weight (Mw) of 8000, polydispersity index of 1.6 and 8 repeating units.