Improving performance of Cs <sub>2</sub> AgBiBr <sub>6</sub> solar cell through constructing gradient energy level with deep‐level hole transport material
Ziyang Xia, Wei Zhang, Cheng Chen, Haoxin Wang, Linqin Wang, Yawei Miao, Xing-Dong Ding, Licheng Sun, Ming Cheng
Abstract
Abstract The valence band offset between Cs 2 AgBiBr 6 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 Cs 2 AgBiBr 6 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 Cs 2 AgBiBr 6 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‐9 H ‐fluoren‐3‐yl)(4‐methoxyphenyl)amino)thiophene‐2,5‐diyl)bis( N ‐(9,9‐dimethyl‐9 H ‐fluoren‐2‐yl)‐ N ,9‐bis(4‐methoxyphenyl)‐9 H ‐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 Cs 2 AgBiBr 6 PSCs.