有機共軛高分子太陽電池具有製程簡易，可製作大面積，質量輕且可撓曲等優點，故能製作出低成本之太陽電池。然而，溶液互溶是在製作有機高分子太陽電池多層結構時最主要的問題之一。本研究分別以高溫烘烤、旋轉潤濕、及緩衝層技術解決此問題。結果發現以丙二醇當緩衝層之技術，能降低溶液互溶的問題，並提高多層結構元件的效率。
本研究以P3HT（poly(3-hexythiophene)）及PCBM（[6,6]-phenyl C61-butyric acid methyl ester）混合(blend)為主動層材料。改良原本的塊材異質接面(bulk heterojunction)結構。在P3HT：PCBM(I layer)比例1:1 wt的主動層之前，旋轉塗佈P3HT比例高的主動層(P layer)在陽極端，之後在陰極端加上P3HT比例少的主動層(N layer)。這種漸層分佈混合材料的結構，同時具有激子（exciton）分離區域面積較大的好處以及較佳的載子傳輸效率，能夠有效地提高太陽電池效率。
研究結果成功地製作出雙層結構元件以及P3HT-rich/blend/PCBM-rich之多層P-I-N結構，發現此結構能抑制操作電壓附近的暗電流，有效降低復合電流。從電路模型的參數萃取觀察到並聯電阻(shunt resistance, Rsh)的增加，使得操作電壓較高及FF的增加。能量轉換效率從2.46%提高到3.35%。
此緩衝層技術對製作多層結構或是串接（tandem）結構提供一個新的方法，其降低漏電流及復合電流的優點，將來可應用在製作大面積元件，而改善大面積化之後，更嚴重的漏電流及復合電流。

Polymer solar cells (PSCs) exhibit many advantages such as processing feasibility, capability of scaling up to large area, light weigh and flexibility. Thus we can fabricate cost-effective solar cells. However, mutual dissolution is one of the main problems for achieving PSCs with multilayer structure. In this work, we solve the problem by high temperature baking, spin-rinsing and buffer layer technique. The results show that this buffer layer technique with glycol would reduce the mutual dissolution problem and enhance the efficiency of multilayer structure devices.
We use blending of P3HT and PCBM as active material in our study. Our main research is to modify the conventional bulk heterojunction (BHJ) structure with buffer layer technique. We spin an extra P3HT-rich layer (P layer) near the anode before a normal layer with 1:1 wt of P3HT/PCBM (I layer) being deposited and insert an extra P3HT-poor layer (N layer) near the cathode. The gradually-distributed active layer allow for efficient exciton separation and better carrier extraction at the same time. Therefore, this leads to a better PCE of PSCs.
We successfully demonstrated bi-layer structure devices and multilayer p-i-n structure of P3HT-rich/blend/PCBM-rich in our study. The result shows that the dark current near operating voltage is suppressed. Besides, the recombination is significantly decreased. From the parameters extracted form the circuit model, an increased shunt resistance (Rsh) is observed. This increased Rsh lead to a higher operating voltage and thus an increased FF. The power conversion efficiency with P-I-N structured is enhanced from 2.46% to 3.35%!
The buffer layer technique can be used as a new approach for fabrication of multilayer PSCs or tandem cells. Besides, the P-I-N structure is benefiting for lowering the leakage current and recombination current. This has potential of being applied in fabrication of large-area PSCs which usually have more leakage path and higher recombination current.

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