Understanding surface chemistry during MAPbI₃ spray deposition and its effect on photovoltaic performance

Abstract

aIn recent years there has been significant research into organic-inorganic halide perovskites for photovoltaic applications and has resulted in power conversion efficiencies greater than 20%. A number of deposition techniques have been utilized to produce high quality perovskite films including thermal evaporation, single and two-step spin coating and vapor assisted processes. However, these laboratory based fabrication methods are not well matched with low costing, roll to roll processing that is associated with large scale manufacture. In this work we use a low costing and rapid spray coating technique to fabricate solution processed MAPbI 3 films with controlled film thickness achieved through modifying concentration/spray volume. Investigation into the chemical composition and film morphology showed differing surface chemistries for the different film thicknesses, altering the surface morphology from large micro grained structures to small distorted grain arrangements. We have then implemented spray deposited films into solar devices (ITO/TiO 2 /MAPbI 3 /Au) and have studied the current density-voltage (JV) characteristics including light soaking effects. Through optimizing the absorber thickness the short-circuit current density is increased from 4.9 mA cm À2 to 22.3 mA cm À2, increasing overall power conversion efficiency by a factor 45. Investigation into the performance of devices under continued illumination showed an inverse relationship existed between low efficiency (thick) MAPbI 3 films and high efficiency (thin) MAPbI 3 films, where the former displayed large increases in overall performance compared to the rapid degradation in the latter. We attribute device instabilities to the increase in defect density as a consequence of the spray-induced surface chemistry, leading to trap assisted recombination at the back electrode.

Doping and Photon Induced Defect Healing of Hybrid Perovskite Thin Films: An Approach Towards Efficient Light Emitting Diodes

“…Moreover, as prepared MAPbBr 3 and MA 0.87 Cs 0.13 PbBr 3 thin films exhibit O1s, and the Pb4 f peak shift at high binding energy obtained at 143.6 eV corresponds to oxidation of PbBr 2 . Similar binding energy values reported previously confirm the presence of PbBr 2 (DMSO)x ,. Upon UV irradiation, MAPbBr 3 thin films still observe traces of PbBr 2 (DMSO) x , but the peak intensity reduces significantly (Figure e).…”

“…Similar binding energy values reported previously confirm the presence of PbBr 2 (DMSO)x. [19,[40][41][42] Upon UV irradiation, MAPbBr 3 thin films still observe traces of PbBr 2 (DMSO) x , but the peak intensity reduces significantly (Figure 1e). On the other hand, PbBr 2 (DMSO) x completely disappears upon UV irradiation of MA 0.87 Cs 0.13 PbBr 3 .…”

Interfaces Between Graphene‐Related Materials and MAPbI3: Insights from First‐Principles

“…The schematic alignment, including the case of pristine graphene, is shown in Figure b. All the energy levels reported are aligned to the measured energy levels of MAPbI 3 referred to vacuum . Interestingly the calculations show that, for high O concentration, a type‐I straddling heterojunction is formed, with the conduction (valence) band of the GRM layer lying at higher (lower) energies than those of MAPbI 3 .…”

“…b) Calculated interface energy‐level alignment for rGO/MAPI interfaces with various O‐concentrations. Energy levels are referred to those measured for MAPbI 3 levels . Adapted with permission .…”

High Performance Inverted Planar MAPbI3 Perovskite Solar Cells with a Simple Annealing Process

“…[23][24][25][26][27][28][29][30][31] In fact, MAPbI 3 can work very long time and stabilize at perovskite phase. [32][33][34] Therefore, it is of significance to optimize the MAPbI 3 PSCs fabrication procedure to obtain high performance devices. [35][36][37] In addition, the reported high performance perovskite solar cells are mainly fabricated and tested in nitrogen glovebox.…”