Improving performance of Cs2AgBiBr6 solar cell through constructing gradient energy level with deep-level hole transport material

The valence band offset between Cs2AgBiBr6 and hole transport layer (HTL) is approximately 1.00 eV, which results in high energy loss and is identified as one of the bottle necks of Cs2AgBiBr6 perovskite solar cell (PSC) for achieving high power conversion efficiency (PCE). To tackle this problem, we propose the optimization of the energy level alignment by designing and synthesizing novel deep-level hole transport materials (HTMs). The sole introduction of deep-level HTMs successfully reduces the valence band offset between Cs2AgBiBr6 and HTL, but induces the increased valence band offset at HTL/Au interface, limiting the PCE improvement. To further solve the problem and improve the PCE, the gradient energy level arrangement is constructed by combining the newly developed deep-level HTM 6,6'-(3-((9,9-dimethyl-9H-fluoren-3-yl)(4-methoxyphenyl)amino)thiophene-2,5-diyl)bis(N-(9,9-dimethyl-9H-fluoren-2-yl)-N,9-bis(4-methoxyphenyl)-9H-carbazol-3-amine) (TF) with 2,2',7,7'-tetrakis(N,N'-di-pmethoxyphenylamine)-9,9-spirobifluorene (Spiro-OMeTAD). Through optimization, an impressive PCE of 3.50% with remarkably high open-circuit voltage (V-oc) and fill factor (FF) is achieved, qualifying it among the best pristine Cs2AgBiBr6 PSCs.

Automated summary

In order to overcome the energy loss caused by the valence band offset between Cs2AgBiBr6 and the hole transport layer (HTL), a novel deep-level hole transport material (HTM) was designed and synthesized to optimize the energy level alignment. While the introduction of deep-level HTMs successfully reduced the valence band offset between Cs2AgBiBr6 and HTL, it also increased the valence band offset at the HTL/Au interface, limiting the improvement of the power conversion efficiency (PCE). To further improve the PCE, a gradient energy level arrangement combining the newly developed deep-level HTM with Spiro-OMeTAD was constructed. Through optimization, an impressive PCE of 3.50% with high open-circuit voltage and fill factor was achieved, making it one of the best Cs2AgBiBr6 perovskite solar cells.