Xiaoyin Xie

A transparent poly(3,4-ethylenedioxylenethiophene):poly(styrene sulfonate) cathode for low temperature processed, metal-oxide free perovskite solar cells

Low temperature processed, metal-oxide free planar perovskite solar cells (PSCs) were fabricated on glass and polyethylene terephthalate (PET) substrates using polyetherimide (PEI) modified poly(3,4-ethylenedioxylenethiophene):poly(styrene sulfonate) (PEDOT:PSS) as the cathode. The modification by PEI significantly changed the work function of PEDOT:PSS from −5.06 to −4.08 eV, yielding better electron transportation. The rigid cell on the glass substrate exhibited a high power conversion efficiency (PCE) of 12.42% without significant hysteresis and comparable to the PCE of PSCs with metal oxide cathodes. Moreover, the stability in air was higher by 32% than that of the devices with metal-oxide cathodes. The flexible device on the PET substrate exhibited a PCE of 9.73% and good bendability. Our results indicate that the flexibility of the PEDOT:PSS/PEI cathode is promising for use in large-scale roll-to-roll production of PSCs.

Improving performance of organic solar cells by supplying additional acceptors to surface of bulk-heterojunction layers

In this study, we improved the performance of poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′] dithiophene-co-3-fluorothieno[3,4-b]thiophene-2-carboxylate]:[6,6]-phenyl-C70-butyric acid methyl ester (PTB7-Th:PC71BM)-based organic solar cells (OSCs) by thermally evaporating additional acceptors PC71BM or 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]dithiophene (ITIC) on the surface of bulk-heterojunction layers. We found that the surface of the bulk-heterojunction layers showed a shortage of acceptor materials due to vertical phase separation, which was detrimental to the power conversion efficiency (PCE). The acceptor addition (PC71BM or ITIC) was beneficial for charge transport and suppressed charge recombination. Addition of a 9 nm PC71BM layer on the surface of the bulk-heterojunction layers significantly improved the performance of rigid OSCs (on glass substrates), and the maximum PCE increased from 8.99% to 10.25%, which was higher than that (9.78%) of the OSCs using ITIC. In addition, the degradation of the OSCs during long-term stability testing reduced from 21% to 14% Furthermore, the PCE of flexible OSCs (on polyethylene naphthalate substrate) improved from 7.65% to 8.52%. Our results indicated that evaporating PC71BM on the surface of bulk-heterojunction layers is a simple and effective method to fabricate high-performance rigid and flexible OSCs.

Improvement of inverted organic solar cells using acetic acid as an additive for ZnO layer processing

In this work, we used acetic acid as an additive for the preparation of ZnO layers and improved the performance of poly{4,8-bis[(2-ethylhexyl)-oxy]benzo[1,2-b:4,5-b’] dithiophene-2,6-diyl-alt-3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophene- 4,6-diyl} (PTB7)-based inverted organic solar cells. The addition of acetic acid to the ZnO precursor solution improved the transparency and conductivity of the sol-gel-synthesized ZnO film, by increasing the grain size of the film. Accordingly, the power conversion efficiency (PCE) of the organic solar cells was improved from 6.42% to 7.55%, which was mainly caused by the enhanced current density and fill factor. The best sample demonstrated a high PCE of 7.85% with negligible hysteresis and good stability. Our results indicate that using acetic acid as an additive for the preparation of ZnO is a simple and effective way of fabricating high-performance inverted organic solar cells.