1.5–1.6 eV bandgap Pb‐based perovskite solar cells (PSCs) with 30–31% theoretical efficiency limit by the Shockley–Queisser model achieve 21–24% power conversion efficiencies (PCEs). However, the best PCEs of reported ideal‐bandgap (1.3–1.4 eV) Sn–Pb PSCs with a higher 33% theoretical efficiency limit are <18%, mainly because of their large open‐circuit voltage (Voc) deficits (>0.4 V). Herein, it is found that the addition of guanidinium bromide (GABr) can significantly improve the structural and photoelectric characteristics of ideal‐bandgap (≈1.34 eV) Sn–Pb perovskite films. GABr introduced in the perovskite films can efficiently reduce the high defect density caused by Sn2+ oxidation in the perovskite, which is favorable for facilitating hole transport, decreasing charge‐carrier recombination, and reducing the Voc deficit. Therefore, the best PCE of 20.63% with a certificated efficiency of 19.8% is achieved in 1.35 eV PSCs, along with a record small Voc deficit of 0.33 V, which is the highest PCE among all values reported to date for ideal‐bandgap Sn–Pb PSCs. Moreover, the GABr‐modified PSCs exhibit significantly improved environmental and thermal stability. This work represents a noteworthy step toward the fabrication of efficient and stable ideal‐bandgap PSCs.
Here, the authors report a highly efficient integrated ideal‐bandgap perovskite/bulk‐heterojunction solar cell (IPBSC) with an inverted architecture, featuring a near infrared (NIR) polymer DTBTI‐based bulk‐heterojunction (BHJ) layer atop guanidinium bromide (GABr)‐modified FA0.7MA0.3Pb0.7Sn0.3I3 perovskite film as the photoactive layer. The IPBSC shows cascade‐like energy level alignment between the charge‐extractionlayer/perovskite/BHJ and efficient passivation effect of BHJ on perovskite. Thanks to the well‐matched energy level alignment and high‐quality ideal bandgap‐based perovskite film, an efficient charge transfer occurs between the charge‐extraction‐layer/perovskite/BHJ. Moreover, the NIR polymer DTBTI on the perovskite film leads to an improved NIR light response for the IPBSC. In addition, the O, S and N atoms in the DTBTI polymer yield a strong interaction with perovskite, which is conducive to reducing the defects of the perovskite and suppressing charge recombination. As a result, the solar cell achieves a power conversion efficiency (PCE) of 24.27% (certificated value at 23.4% with 0.283‐volt voltage loss), currently the recorded efficiency for both IPBSCs and Pb‐Sn alloyed PSCs, and which is over the highest efficiency of perovskite–organic tandem solar cell. Moreover, the thermal, humidity and long‐term operational stabilities of the IPBSCs are also significantly improved compared with the control PSCs.
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