Tuning Device Interfaces for Improved Open Circuit Voltage in Wide-bandgap Hybrid Perovskite Photovoltaics

Wide-bandgap hybrid organic-inorganic perovskite solar cells (PSCs) are of interest to the research community because of their potential for high performance, low-cost and lightweight integration as persistent photovoltaic (PV) sources for tandem PV, space, expeditionary, and underwater power generation. However, despite recent advancements in hybrid PSCs with bandgaps close to 1.75 eV, there are fewer research efforts exploring single-junction PSCs with band gaps 1.8 - 2.1 eV. Here, we show the solution-processed fabrication of a wide-bandgap hybrid PSCs utilizing a formamidinium-based mixed iodide/bromide perovskite composition (band gap similar to 1.84 eV) as the active layer. Additionally, we employ solution-processable electron and hole transport materials, SnO2, and poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA). Our work illustrates the pivotal role that interfaces between the transport materials and the perovskite layer play on the open circuit voltage (V-OC) of these devices. For example, we observe an increase in the V-OC of devices when we add a C-60-SAM (4-(1',5'-dihydro-1'-methyl-2'H-[5,6]fullereno-C-60-I-h-[1,9-c]pyrrol-2'-yl)benzoic acid) interlayer between the SnO2 and perovskite layer, as well as utilizing effective p-type doping of the hole transport layer. We hypothesize that these results are due to an improved energetic band alignment and/or improved charge extraction efficiencies at those interfaces. Through careful manipulation of perovskite/transport material interfaces, we can achieve wide-bandgap hybrid PSCs with a V-OC greater than 1.1 V. This study is one of only a few detailed works into single-junction PSCs with a bandgap > 1.75 eV utilizing a hybrid formamidinium-based perovskite composition.