Abstract
To fabricate high-performance metal-halide perovskite solar cells, a thermal annealing process is indispensable in preparing high quality perovskite film. And usually such annealing is performed on hot plate. However hot-plate annealing could cause problems such as inhomogeneous heating (induced by non-tight contact between the sample and the plate), it is also not fit for large scale manufactory. In this paper, we conduct the annealing process in air-heated oven under various humidity environments, and compared the resulted films (CH3NH3PbI3−xClx) and devices (Al/PC61BM/CH3NH3PbI3−xClx/PEDOT:PSS/ITO/glass) with that obtained via hot-plate annealing. It is found that the air-heated-oven annealing is superior to the hot-plate annealing: the annealing time is shorter, the films are more uniform, and the devices exhibit higher power conversion efficiency and better uniformity. The highest efficiencies achieved for the oven and hot-plate annealing processes are 14.9% and 13.5%, and the corresponding standard deviations are 0.5% and 0.8%, respectively. Our work here indicates that air-heated-oven annealing could be a more reliable and more efficient way for both lab research and large-scale production.
Highlights
Contact the surface of the hot plate, which requires very flat surfaces for both the hot plate and the bottom of the sample
It is seen that for the P films, there are many small pin-holes under a relative humidity (RH) of 10%, and there are less and less pin-holes with the RH increasing to 20% and 30%, and their sizes becomes smaller and smaller
The tendency continues with increasing the RH to 50%, larger crystals form and the film breaks in certain areas
Summary
Even for the crystals formed at high humidity levels (50% to 90% RH), they are much more uniform in size for the O films. From these images it can be concluded that the humidity has great influence over the formation of the perovskite film during the annealing process. The O device almost always shows superior VOC/JSC/FF/PCE over the P device under each humidity condition. The large gap area between the crystals might be covered by a CH3NH3PbI3−xClx thin film, which together with the PC61BM layer could prevent possible large current leakage between the anode and the cathode, and the device still can maintain a normal behavior. Thereby these gap areas play a negative role of dragging down the overall light current density of the device and pushing up the overall dark current density of the device, and as a result, leading to smaller JSC, VOC, and FF
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