Photovoltaic solar cells based on perovskite materials due to their unique optoelectronic properties are good instruments to develop green energy for worldwide energy demands. In perovskite solar cells (PSCs), a high performance of 25.8% was reported, employing an expensive Spiro-OMeTAD hole transport layer. Here, the study is focused on PSCs without any HTLs (HTL-free PSCs) to reduce the fabrication process costs. The electron transport layers (ETLs) are treated with tetramethylammonium hydroxide (TMAOH) to improve the efficiency of HTL-free devices. By employing a treatment step, the conductivity of ETLs is increased while their transparency is kept safe. The improved conductivity leads to accelerated charge transport within the device and reduces electron−hole recombination. The perovskite layers fabricated on the treated ETLs showed lower surface defects due to better spreading of the perovskite solution on them. The reduced surface defects cause improvements in the photovoltaic performance of HTL-free PSCs, leading to a stability increment due to lower surface defects for the reaction of humidity with the perovskite layer. TMAOH treatment results in PSCs with a maximum PCE of 13.24%, higher than the 10.88% for control devices.
Hole transport material-free perovskite solar cells (HF-PSCs) offer low-cost photovoltaic devices. For development and commercialization, they are more attractive than the expensive HTLcontained perovskite solar cells. Herein, we focused on enhancing the stability and efficiency of HF-PSCs with the malonic acid (MA) addition to the methylammonium lead iodide. The introduced additive increases the perovskite crystallinity and assembles a perovskite layer with larger grains along with fewer surface defects. In addition, the MA-modified HF-PSCs show suppressed charge recombination within devices, and a lower charge trap density has been obtained for them. A considerable power conversion efficiency of 14.14% is achieved for MA-modified HF-PSCs, higher than the performance of 11.88% for the untreated HF-PSCs. Finally, MA-based HF-PSCs show higher shelf stability than the control HF-PSCs. It is because the MA-modified perovskite layer with passivated grain boundaries is better at repelling water.
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