Bharti, Vishal and Sharma, Abhishek and Gupta, Vinay and Sharma, Gauri D. and Chand, Suresh
(2016)
Improved hole mobility and suppressed trap density in polymer-polymer dual donor based highly efficient organic solar cells.
Applied Physics Letters, 108 (7).
ISSN 0003-6951
Abstract
Here we report, the charge transport properties of polymer-polymer dual donor blended film, viz., polythieno[3,4-b]-thiophene-co-benzodithiophene (PTB7) and poly [N-9 ''-hepta-decanyl-2,7-carbazole-alt-5,5-(4 ',7 '-di-2-thienyl-2 ',1 ',3 ' benzothiadiazole) (PCDTBT) in the optimized concentration. Trap density and hole mobility in polymer-polymer (PTB7-PCDTBT) dual donor system have been studied by means of current density-voltage (J-V) characteristics at various temperatures, i.e., 280 K-120K in hole only device configuration, i.e., indium tin oxide/poly(3,4-ethylenedioxythiophene):poly(styrenesulphonate) (PEDOT:PSS)/Polymer film/gold (Au). The J-V curves exhibit the space charge limited conduction behavior. The corresponding hole mobility for PTB7 and PCDTBT are 3.9 x 10(-4) cm(2) V-1 s(-1) and 2.1 x 10(-4) cm(2) V-1 s(-1), respectively, whereas it is 9.1 x 10(-4) cm(2) V-1 s(-1) in the polymer-polymer blend of PTB7: PCDTBT (0.7:0.3). This enhancement in mobility can be attributed to the suppressed trap density in PTB7: PCDTBT (0.7: 0.3) of 7.4 x 10(16) cm(-3), as compared to the trap density of 1.1 x 10(17) cm(-3) for PTB7 and 1.6 x 10(17) cm(-3) for PCDTBT. Atomic force microscopy shows an improvement in the morphology of the blend. The J-V characteristic at various light intensities in the bulk heterojunction (BHJ) solar cell reveals that the blending of PCDTBT in PTB7 suppressed the trap-assisted recombination. The corresponding power conversion efficiencies for PTB7:PC71BM, PCDTBT:PC71BM and PTB7:PCDTBT:PC71BM BHJ solar cells are 6.9%, 6.1% and 9.0%, respectively. This work unravels that the enhanced mobility and suppressed trap density play a significant role in the improvement of efficiency in dual donor based organic solar cells.
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