The biochars derived from nine kinds of leaves by one-step pyrolysis were employed as counter electrodes in dye-sensitized solar cells (DSSCs). Based on comprehensive analysis on the microstructure

crystal structure and electrochemical properties of biochars

the intrinsic causes to induce the difference of the photovoltaic properties of the biochars based DSSCs were investigated emphatically. The results indicated that the conversion efficiencies of DSSCs consisting of biochars counter electrodes derive from various leaves ranged from 1.00% to 1.85%. Among them

the palm leaf bring about the best efficiency

followed by camphor leaf

poplar leaf

maple leaf

red after-wood leaf

toona leaf

firry leaf and pine needles

and the cassia leaf with the least efficiency. The pore structure of biochars was believed as one of key factors to induce the difference of the photovoltaic properties of the DSSCs. Since the biochar prepared from palm leaf possessed unique oriented pore structure which could shorten the diffusion length of electrolyte and improve the catalytic activities

the DSSC with the best efficiency was obtained. Especially

all the biochars based DSSCs showed higher efficiency than the graphite based device. The efficiency of the graphite based DSSC is 0.77%. The high performance of biochars based DSSCs can be attributed to the favorable characteristics of the biochars

such as hierarchical pore structure and glassy carbon skeleton. The low temperature (120℃) treatment process can be employed to fabricate a low-cost counter electrode for both glass based DSSCs and flexible DSSCs.