Tin oxide (SnO 2 ) is widely used in perovskite solar cells (PSCs) as an electron transport layer (ETL) material. However, its high surface trap density has already become a strong factor limiting PSC development. In this work, phosphoric acid is adopted to eliminate the SnO 2 surface dangling bonds to increase electron collection efficiency. The phosphorus mainly exists at the boundaries in the form of chained phosphate groups, bonding with which more than 47.9% of Sn dangling bonds are eliminated. The reduction of surface trap states depresses the electron transport barriers, thus the electron mobility increases about 3 times when the concentration of phosphoric acid is optimized with 7.4 atom % in the SnO 2 precursor. Furthermore, the stability of the perovskite layer deposited on the phosphate-passivated SnO 2 (P-SnO 2 ) ETL is gradually improved with an increase of the concentration. Due to the higher electron collection efficiency, the P-SnO 2 ETLs can dramatically promote the power conversion efficiency (PCE) of the PSCs. As a result, the champion PSC has a PCE of 21.02%. Therefore, it has been proved that this simple method is efficient to improve the quality of ETL for high-performance PSCs.
Heterojunction solar cells (HSCs) featuring half and full contact of poly (3,4-ethylenedioxythiophene):polystyrene (PE-DOT:PSS) with pyramid-textured silicon (Si) were thoroughly compared via simulations and experiments, and the following conclusions have been reached: (1) The insufficient electrical passivation inherent to the half contact results in enormous decline in short-circuit current density (J sc ) and open-circuit voltage (V oc ). ( 2) For the full-contact HSCs, J sc is mainly dependent on the recombination at the rear interface. With tuning of the contact properties from both sides, calculated (experimental) efficiencies of 14.46%/16.89% (13.94%/16.21%) for the half-/full-contact HSCs were finally obtained. A superior power conversion efficiency (PCE) over 21% is further predicted by considering more optimal contact resistance as well as doping concentration of Si. Our findings clarify why textured-Si/PEDOT:PSS HSCs show V oc and PCE that are inferior to those of planar counterparts in previous reports and further suggest a pathway to fully explore the efficiency potential of Si/PEDOT:PSS hybrid solar cells.
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